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expect




SYNOPSIS

       expect [ -dDinN ] [ -c cmds ] [ -[f|b] ] cmdfile ] [  args
       ]


INTRODUCTION

       Expect is a program that "talks" to other interactive pro­
       grams according to a script.  Following the script, Expect
       knows  what  can  be  expected from a program and what the
       correct response should be.  An interpreted language  pro­
       vides  branching  and  high-level  control  structures  to
       direct the dialogue.  In addition, the user can take  con­
       trol and interact directly when desired, afterward return­
       ing control to the script.

       Expectk is a mixture of Expect and Tk.   It  behaves  just
       like  Expect  and  Tk's  wish.   Expect  can  also be used
       directly in C or C++ (that is, without Tcl).   See  libex­
       pect(3).

       The  name  "Expect"  comes  from  the  idea of send/expect
       sequences popularized by uucp, kermit and other modem con­
       trol programs.  However unlike uucp, Expect is generalized
       so that it can be run as a  user-level  command  with  any
       program  and  task  in  mind.  Expect can actually talk to
       several programs at the same time.

       For example, here are some things Expect can do:

              ·   Cause your computer to dial you back,  so  that
                  you can login without paying for the call.

              ·   Start  a  game (e.g., rogue) and if the optimal
                  configuration doesn't appear, restart it (again
                  and  again)  until it does, then hand over con­
                  trol to you.

              ·   Run fsck, and in  response  to  its  questions,
                  answer "yes", "no" or give control back to you,
                  based on predetermined criteria.

              ·   Connect to another network or  BBS  (e.g.,  MCI
                  Mail,  CompuServe)  and  automatically retrieve
                  your mail so that it appears as if it was orig­
                  inally sent to your local system.

              ·   Carry environment variables, current directory,
                  or any kind of information across rlogin,  tel­
                  net, tip, su, chgrp, etc.

       There  are  a variety of reasons why the shell cannot per­
       form these tasks.  (Try, you'll see.)   All  are  possible
       and making the first line in your script:

           #!/usr/local/bin/expect -f

       Of course, the path must accurately describe where  Expect
       lives.  /usr/local/bin is just an example.

       The  -c  flag prefaces a command to be executed before any
       in the script.  The command should be  quoted  to  prevent
       being  broken  up  by  the shell.  This option may be used
       multiple times.  Multiple commands may be executed with  a
       single  -c  by  separating them with semicolons.  Commands
       are executed  in  the  order  they  appear.   (When  using
       Expectk, this option is specified as -command.)

       The  -d flag enables some diagnostic output, which primar­
       ily reports internal activity of commands such  as  expect
       and   interact.    This   flag  has  the  same  effect  as
       "exp_internal 1" at the beginning  of  an  Expect  script,
       plus  the  version of Expect is printed.  (The strace com­
       mand is useful for tracing statements, and the trace  com­
       mand  is  useful for tracing variable assignments.)  (When
       using Expectk, this option is specified as -diag.)

       The -D flag enables an interactive debugger.   An  integer
       value  should  follow.   The  debugger  will  take control
       before the next Tcl procedure if the value is non-zero  or
       if  a  ^C  is  pressed  (or  a breakpoint is hit, or other
       appropriate debugger command appears in the script).   See
       the  README  file or SEE ALSO (below) for more information
       on the debugger.  (When  using  Expectk,  this  option  is
       specified as -Debug.)

       The  -f  flag  prefaces a file from which to read commands
       from.  The flag itself is optional as it  is  only  useful
       when  using  the  #!  notation  (see above), so that other
       arguments may be supplied  on  the  command  line.   (When
       using Expectk, this option is specified as -file.)

       By  default, the command file is read into memory and exe­
       cuted in its entirety.  It is  occasionally  desirable  to
       read files one line at a time.  For example, stdin is read
       this way.  In order to force arbitrary files to be handled
       this  way,  use  the  -b  flag.  (When using Expectk, this
       option is specified as -buffer.)

       If the string "-" is  supplied  as  a  filename,  standard
       input  is  read  instead.   (Use "./-" to read from a file
       actually named "-".)

       The -i flag causes Expect to interactively prompt for com­
       mands  instead  of reading them from a file.  Prompting is

       Note  that  the  usual getopt(3) and execve(2) conventions
       must be observed when adding arguments to the #! line.

       The file $exp_library/expect.rc is  sourced  automatically
       if  present,  unless  the  -N  flag  is used.  (When using
       Expectk, this option is specified as -NORC.)   Immediately
       after  this,  the  file  ~/.expect.rc is sourced automati­
       cally, unless the -n flag is  used.   If  the  environment
       variable  DOTDIR  is defined, it is treated as a directory
       and .expect.rc is read from there.  (When  using  Expectk,
       this  option is specified as -norc.)  This sourcing occurs
       only after executing any -c flags.

       -v causes Expect to print its  version  number  and  exit.
       (The  corresponding  flag in Expectk, which uses long flag
       names, is -version.)

       Optional args are constructed into a list  and  stored  in
       the  variable  named  argv.   argc  is  initialized to the
       length of argv.

       argv0 is defined to be the name of the script  (or  binary
       if  no script is used).  For example, the following prints
       out the name of the script and the first three arguments:

           send_user "$argv0 [lrange $argv 0 2]\n"


COMMANDS

       Expect uses Tcl (Tool  Command  Language).   Tcl  provides
       control flow (e.g., if, for, break), expression evaluation
       and several other features such  as  recursion,  procedure
       definition,  etc.   Commands  used  here  but  not defined
       (e.g., set, if,  exec)  are  Tcl  commands  (see  tcl(3)).
       Expect  supports  additional  commands,  described  below.
       Unless otherwise  specified,  commands  return  the  empty
       string.

       Commands  are  listed  alphabetically  so that they can be
       quickly located.  However, new users may find it easier to
       start  by reading the descriptions of spawn, send, expect,
       and interact, in that order.

       Note that the best  introduction  to  the  language  (both
       Expect and Tcl) is provided in the book "Exploring Expect"
       (see SEE ALSO below).  Examples are included in  this  man
       page  but  they  are  very  limited since this man page is
       meant primarily as reference material.

       Note that in the text of this man page, "Expect"  with  an
       uppercase  "E" refers to the Expect program while "expect"

             The -onexec flag determines  whether  the  spawn  id
             will  be  closed  in any new spawned processes or if
             the process is overlayed.  To leave a spawn id open,
             use  the  value  0.   A  non-zero integer value will
             force the spawn closed (the default) in any new pro­
             cesses.

             The -slave flag closes the slave associated with the
             spawn id.  (See "spawn -pty".)  When the  connection
             is closed, the slave is automatically closed as well
             if still open.

             No matter whether the connection is  closed  implic­
             itly or explicitly, you should call wait to clear up
             the corresponding kernel process slot.   close  does
             not call wait since there is no guarantee that clos­
             ing a process connection will cause it to exit.  See
             wait below for more info.

       debug [[-now] 0|1]
             controls a Tcl debugger allowing you to step through
             statements, set breakpoints, etc.

             With no arguments, a 1 is returned if  the  debugger
             is not running, otherwise a 0 is returned.

             With  a 1 argument, the debugger is started.  With a
             0 argument, the debugger is stopped.  If a  1  argu­
             ment  is  preceded by the -now flag, the debugger is
             started immediately (i.e.,  in  the  middle  of  the
             debug  command  itself).  Otherwise, the debugger is
             started with the next Tcl statement.

             The debug command does not change any  traps.   Com­
             pare  this  to starting Expect with the -D flag (see
             above).

             See the README file or SEE  ALSO  (below)  for  more
             information on the debugger.

       disconnect
             disconnects  a forked process from the terminal.  It
             continues running in the background.  The process is
             given its own process group (if possible).  Standard
             I/O is redirected to /dev/null.

             The following fragment uses disconnect  to  continue
             running the script in the background.

                 if {[fork]!=0} exit
                 disconnect
                     spawn priv_prog
                     expect Password:
                     send "$expect_out(1,string)\r"
                     . . .
                     exit
                 }

             An advantage to  using  disconnect  over  the  shell
             asynchronous  process feature (&) is that Expect can
             save the terminal parameters prior to disconnection,
             and  then  later  apply  them  to new ptys.  With &,
             Expect does not have a chance to read the terminal's
             parameters  since  the  terminal  is already discon­
             nected by the time Expect receives control.

       exit [-opts] [status]
             causes Expect to exit or otherwise prepare to do so.

             The -onexit flag causes the next argument to be used
             as an exit handler.  Without an argument,  the  cur­
             rent exit handler is returned.

             The  -noexit  flag  causes Expect to prepare to exit
             but stop short of actually returning control to  the
             operating  system.  The user-defined exit handler is
             run as well as Expect's own internal  handlers.   No
             further Expect commands should be executed.  This is
             useful if you are  running  Expect  with  other  Tcl
             extensions.   The current interpreter (and main win­
             dow if in the Tk environment) remain so  that  other
             Tcl  extensions  can  clean up.  If Expect's exit is
             called again (however this might  occur),  the  han­
             dlers are not rerun.

             Upon  exiting,  all connections to spawned processes
             are closed.  Closure will be detected as an  EOF  by
             spawned  processes.   exit  takes  no  other actions
             beyond what  the  normal  _exit(2)  procedure  does.
             Thus,  spawned  processes  that do not check for EOF
             may continue to run.  (A variety of  conditions  are
             important  to determining, for example, what signals
             a spawned process will be sent, but these  are  sys­
             tem-dependent,  typically documented under exit(3).)
             Spawned processes  that  continue  to  run  will  be
             inherited by init.

             status  (or  0  if not specified) is returned as the
             exit status of Expect.  exit is implicitly  executed
             if the end of the script is reached.

       exp_continue [-continue_timer]
             The  command  exp_continue  allows  expect itself to
             If  the  optional  file  is supplied, all normal and
             debugging output is written to that file (regardless
             of  the  value  of  value).  Any previous diagnostic
             output file is closed.

             The -info  flag  causes  exp_internal  to  return  a
             description  of  the  most recent non-info arguments
             given.

       exp_open [args] [-i spawn_id]
             returns a Tcl file identifier  that  corresponds  to
             the original spawn id.  The file identifier can then
             be used as if it were opened by Tcl's open  command.
             (The  spawn  id  should  no  longer be used.  A wait
             should not be executed.

             The -leaveopen flag leaves the  spawn  id  open  for
             access through Expect commands.  A wait must be exe­
             cuted on the spawn id.

       exp_pid [-i spawn_id]
             returns the process id  corresponding  to  the  cur­
             rently spawned process.  If the -i flag is used, the
             pid returned corresponds to that of the given  spawn
             id.

       exp_send
             is an alias for send.

       exp_send_error
             is an alias for send_error.

       exp_send_log
             is an alias for send_log.

       exp_send_tty
             is an alias for send_tty.

       exp_send_user
             is an alias for send_user.

       exp_version [[-exit] version]
             is useful for assuring that the script is compatible
             with the current version of Expect.

             With no arguments, the current version of Expect  is
             returned.   This version may then be encoded in your
             script.  If you actually know that you are not using
             features of recent versions, you can specify an ear­
             lier version.

             Versions consist of three numbers separated by dots.
             Expect  software distribution is changed in any way,
             such as by additional documentation or optimization.
             It is reset to 0 upon each new minor version.

             With  the  -exit  flag,  Expect  prints an error and
             exits if the version is out of date.

       expect [[-opts] pat1 body1] ... [-opts] patn [bodyn]
             waits until one of the patterns matches  the  output
             of  a  spawned  process, a specified time period has
             passed, or an end-of-file is  seen.   If  the  final
             body is empty, it may be omitted.

             Patterns  from the most recent expect_before command
             are implicitly used before any other patterns.  Pat­
             terns  from the most recent expect_after command are
             implicitly used after any other patterns.

             If the arguments  to  the  entire  expect  statement
             require more than one line, all the arguments may be
             "braced" into one so as to  avoid  terminating  each
             line  with a backslash.  In this one case, the usual
             Tcl substitutions will occur despite the braces.

             If a pattern is the keyword eof,  the  corresponding
             body  is executed upon end-of-file.  If a pattern is
             the keyword timeout, the corresponding body is  exe­
             cuted  upon timeout.  If no timeout keyword is used,
             an implicit null action is  executed  upon  timeout.
             The  default timeout period is 10 seconds but may be
             set, for example to 30, by the command "set  timeout
             30".   An  infinite timeout may be designated by the
             value -1.  If a pattern is the keyword default,  the
             corresponding  body  is executed upon either timeout
             or end-of-file.

             If a pattern matches, then the corresponding body is
             executed.  expect returns the result of the body (or
             the empty string if no  pattern  matched).   In  the
             event  that multiple patterns match, the one appear­
             ing first is used to select a body.

             Each time new output arrives, it is compared to each
             pattern in the order they are listed.  Thus, you may
             test for absence of a match by making the last  pat­
             tern  something  guaranteed  to  appear,  such  as a
             prompt.  In situations where there is no prompt, you
             must  use  timeout  (just like you would if you were
             interacting manually).

             Patterns are specified in three ways.   By  default,
             patterns  are  specified  as with Tcl's string match
                     busy               {puts busy\n ; exp_continue}
                     failed             abort
                     "invalid password" abort
                     timeout            abort
                     connected
                 }

             Quotes are necessary on the fourth pattern since  it
             contains a space, which would otherwise separate the
             pattern from the action.   Patterns  with  the  same
             action (such as the 3rd and 4th) require listing the
             actions again.  This can be avoid by  using  regexp-
             style  patterns  (see  below).   More information on
             forming glob-style patterns can be found in the  Tcl
             manual.

             Regexp-style  patterns  follow the syntax defined by
             Tcl's regexp (short for "regular  expression")  com­
             mand.   regexp patterns are introduced with the flag
             -re.  The previous example can be rewritten using  a
             regexp as:

                 expect {
                     busy       {puts busy\n ; exp_continue}
                     -re "failed|invalid password" abort
                     timeout    abort
                     connected
                 }

             Both types of patterns are "unanchored".  This means
             that patterns  do  not  have  to  match  the  entire
             string,  but can begin and end the match anywhere in
             the string (as long  as  everything  else  matches).
             Use  ^  to match the beginning of a string, and $ to
             match the end.  Note that if you do not wait for the
             end of a string, your responses can easily end up in
             the middle of the string as they are echoed from the
             spawned  process.   While  still  producing  correct
             results, the output can look unnatural.   Thus,  use
             of  $  is encouraged if you can exactly describe the
             characters at the end of a string.

             Note that in many editors, the ^  and  $  match  the
             beginning  and  end  of lines respectively. However,
             because expect is not line oriented,  these  charac­
             ters  match  the  beginning  and end of the data (as
             opposed to lines) currently in the  expect  matching
             buffer.   (Also, see the note below on "system indi­
             gestion.")

             The -ex flag causes the pattern to be matched as  an
             "exact"  string.   No interpretation of *, ^, etc is
             been received and no other  patterns  have  matched.
             Whether  or not the full_buffer keyword is used, the
             forgotten     characters     are     written      to
             expect_out(buffer).

             If  patlist  is  the  keyword  null,  and  nulls are
             allowed (via the remove_nulls command),  the  corre­
             sponding  body  is  executed  if a single ASCII 0 is
             matched.  It is not possible to match  0  bytes  via
             glob or regexp patterns.

             Upon matching a pattern (or eof or full_buffer), any
             matching and previously unmatched output is saved in
             the  variable  expect_out(buffer).   Up  to 9 regexp
             substring  matches  are  saved  in   the   variables
             expect_out(1,string)  through  expect_out(9,string).
             If the -indices flag is used before a  pattern,  the
             starting  and ending indices (in a form suitable for
             lrange) of the 10 strings are stored  in  the  vari­
             ables   expect_out(X,start)   and  expect_out(X,end)
             where X is a digit,  corresponds  to  the  substring
             position  in  the buffer.  0 refers to strings which
             matched the entire pattern and is generated for glob
             patterns  as  well as regexp patterns.  For example,
             if a process has produced  output  of  "abcdefgh\n",
             the result of:

                 expect "cd"

             is as if the following statements had executed:

                 set expect_out(0,string) cd
                 set expect_out(buffer) abcd

             and  "efgh\n"  is  left  in the output buffer.  If a
             process produced the  output  "abbbcabkkkka\n",  the
             result of:

                 expect -indices -re "b(b*).*(k+)"

             is as if the following statements had executed:

                 set expect_out(0,start) 1
                 set expect_out(0,end) 10
                 set expect_out(0,string) bbbcabkkkk
                 set expect_out(1,start) 2
                 set expect_out(1,end) 3
                 set expect_out(1,string) bb
                 set expect_out(2,start) 10
                 set expect_out(2,end) 10
                 set expect_out(2,string) k
                 set expect_out(buffer) abbbcabkkkk

             expect_out(spawn_id).

             The -timeout flag causes the current expect  command
             to  use  the following value as a timeout instead of
             using the value of the timeout variable.

             By default, patterns are matched against output from
             the  current  process,  however the -i flag declares
             the output from the named spawn_id list  be  matched
             against  any following patterns (up to the next -i).
             The spawn_id list should either be a whitespace sep­
             arated  list of spawn_ids or a variable referring to
             such a list of spawn_ids.

             For example, the following example waits  for  "con­
             nected"   from   the  current  process,  or  "busy",
             "failed" or "invalid  password"  from  the  spawn_id
             named by $proc2.

                 expect {
                     -i $proc2 busy {puts busy\n ; exp_continue}
                     -re "failed|invalid password" abort
                     timeout abort
                     connected
                 }

             The value of the global variable any_spawn_id may be
             used to match patterns to  any  spawn_ids  that  are
             named  with all other -i flags in the current expect
             command.  The spawn_id from a -i flag with no  asso­
             ciated   pattern   (i.e.,  followed  immediately  by
             another -i) is made available to any other  patterns
             in   the   same   expect   command  associated  with
             any_spawn_id.

             The -i flag may also name a global variable in which
             case  the  variable is read for a list of spawn ids.
             The variable is reread whenever  it  changes.   This
             provides  a way of changing the I/O source while the
             command is in execution.  Spawn  ids  provided  this
             way are called "indirect" spawn ids.

             Actions  such  as  break  and continue cause control
             structures (i.e., for, proc) to behave in the  usual
             way.   The command exp_continue allows expect itself
             to continue executing rather than  returning  as  it
             normally would.

             This  is  useful  for  avoiding  explicit  loops  or
             repeated expect statements.  The  following  example
             is  part  of  a  fragment  to  automate rlogin.  The
             exp_continue avoids having to write a second  expect
                         exit
                     } timeout {
                         send_user "connection to $host timed out\n"
                         exit
                     } eof {
                         send_user \
                             "connection to host failed: $expect_out(buffer)"
                         exit
                     } -re $prompt
                 }

             For example, the following  fragment  might  help  a
             user  guide  an  interaction that is already totally
             automated.  In this case, the terminal is  put  into
             raw  mode.   If  the user presses "+", a variable is
             incremented.  If "p" is pressed, several returns are
             sent to the process, perhaps to poke it in some way,
             and "i" lets the user  interact  with  the  process,
             effectively  stealing  away control from the script.
             In each case, the exp_continue  allows  the  current
             expect  to continue pattern matching after executing
             the current action.

                 stty raw -echo
                 expect_after {
                     -i $user_spawn_id
                     "p" {send "\r\r\r"; exp_continue}
                     "+" {incr foo; exp_continue}
                     "i" {interact; exp_continue}
                     "quit" exit
                 }

             By default, exp_continue resets the  timeout  timer.
             The  timer  is  not  restarted,  if  exp_continue is
             called with the -continue_timer flag.

       expect_after [expect_args]
             works identically to the expect_before  except  that
             if  patterns  from  both expect and expect_after can
             match,  the  expect  pattern  is  used.    See   the
             expect_before command for more information.

       expect_background [expect_args]
             takes  the  same  arguments  as  expect,  however it
             returns immediately.  Patterns are  tested  whenever
             new  input arrives.  The pattern timeout and default
             are  meaningless  to   expect_background   and   are
             silently  discarded.   Otherwise,  the  expect_back­
             ground command uses expect_before  and  expect_after
             patterns just like expect does.


       expect_before [expect_args]
             takes the  same  arguments  as  expect,  however  it
             returns  immediately.  Pattern-action pairs from the
             most recent expect_before with the same spawn id are
             implicitly  added  to any following expect commands.
             If a pattern matches, it is treated  as  if  it  had
             been specified in the expect command itself, and the
             associated body is executed in the  context  of  the
             expect command.  If patterns from both expect_before
             and expect can match, the expect_before  pattern  is
             used.

             If  no  pattern  is  specified,  the spawn id is not
             checked for any patterns.

             Unless overridden by a -i flag,  expect_before  pat­
             terns match against the spawn id defined at the time
             that the expect_before  command  was  executed  (not
             when its pattern is matched).

             The  -info  flag  causes expect_before to return the
             current specifications  of  what  patterns  it  will
             match.   By default, it reports on the current spawn
             id.  An optional spawn id specification may be given
             for information on that spawn id.  For example

                 expect_before -info -i $proc

             At  most  one  spawn  id specification may be given.
             The flag -indirect suppresses direct spawn ids  that
             come only from indirect specifications.

             Instead of a spawn id specification, the flag "-all"
             will cause "-info" to report on all spawn ids.

             The output of the -info flag can be  reused  as  the
             argument to expect_before.

       expect_tty [expect_args]
             is like expect but it reads characters from /dev/tty
             (i.e. keystrokes from the user).  By default,  read­
             ing  is  performed in cooked mode.  Thus, lines must
             end with a return in order for expect to  see  them.
             This  may  be changed via stty (see the stty command
             below).

       expect_user [expect_args]
             is like expect but it reads  characters  from  stdin
             (i.e.  keystrokes from the user).  By default, read­
             ing is performed in cooked mode.  Thus,  lines  must
             end  with  a return in order for expect to see them.
             allowed to write to the log files.  If  you  do  not
             disable  debugging  or  logging  in most of the pro­
             cesses, the result can be confusing.

             Some pty implementations may be confused by multiple
             readers  and writers, even momentarily.  Thus, it is
             safest to fork before spawning processes.

       interact [string1 body1] ... [stringn [bodyn]]
             gives control of the current process to the user, so
             that keystrokes are sent to the current process, and
             the stdout and stderr of  the  current  process  are
             returned.

             String-body  pairs may be specified as arguments, in
             which case the body is executed when the correspond­
             ing  string  is entered.  (By default, the string is
             not sent to the current process.)   The  interpreter
             command is assumed, if the final body is missing.

             If  the  arguments  to the entire interact statement
             require more than one line, all the arguments may be
             "braced"  into  one  so as to avoid terminating each
             line with a backslash.  In this one case, the  usual
             Tcl substitutions will occur despite the braces.

             For  example,  the  following  command runs interact
             with the following string-body pairs defined:   When
             ^Z  is  pressed,  Expect  is suspended.  (The -reset
             flag restores  the  terminal  modes.)   When  ^A  is
             pressed,  the  user sees "you typed a control-A" and
             the process is sent a ^A.  When $  is  pressed,  the
             user  sees  the  date.   When  ^C is pressed, Expect
             exits.  If "foo" is entered, the  user  sees  "bar".
             When  ~~  is  pressed,  the  Expect interpreter runs
             interactively.

                 set CTRLZ \032
                 interact {
                     -reset $CTRLZ {exec kill -STOP [pid]}
                     \001   {send_user "you typed a control-A\n";
                             send "\001"
                            }
                     $      {send_user "The date is [exec date]."}
                     \003   exit
                     foo    {send_user "bar"}
                     ~~
                 }

             In string-body pairs, strings  are  matched  in  the
             order  they  are  listed as arguments.  Strings that
             interact flags from doing so.  Any pattern beginning
             with  a  "-"  should  be protected this way.    (All
             strings starting with "-" are  reserved  for  future
             options.)

             The  -re flag forces the string to be interpreted as
             a regexp-style pattern.  In this case, matching sub­
             strings are stored in the variable interact_out sim­
             ilarly to the way expect stores its  output  in  the
             variable expect_out.  The -indices flag is similarly
             supported.

             The pattern eof introduces an action  that  is  exe­
             cuted  upon end-of-file.  A separate eof pattern may
             also follow the -output flag in  which  case  it  is
             matched  if an eof is detected while writing output.
             The default eof action is "return", so that interact
             simply returns upon any EOF.

             The  pattern  timeout  introduces a timeout (in sec­
             onds) and action that is executed after  no  charac­
             ters  have  been read for a given time.  The timeout
             pattern applies to the most recently specified  pro­
             cess.   There  is  no  default timeout.  The special
             variable "timeout" (used by the expect command)  has
             no affect on this timeout.

             For  example,  the following statement could be used
             to autologout users who have not typed anything  for
             an hour but who still get frequent system messages:

                 interact -input $user_spawn_id timeout 3600 return -output \
                     $spawn_id

             If  the  pattern  is the keyword null, and nulls are
             allowed (via the remove_nulls command),  the  corre­
             sponding  body  is  executed  if a single ASCII 0 is
             matched.  It is not possible to match  0  bytes  via
             glob or regexp patterns.

             Prefacing a pattern with the flag -iwrite causes the
             variable interact_out(spawn_id) to  be  set  to  the
             spawn_id which matched the pattern (or eof).

             Actions  such  as  break  and continue cause control
             structures (i.e., for, proc) to behave in the  usual
             way.   However  return  causes interact to return to
             its caller, while inter_return  causes  interact  to
             cause a return in its caller.  For example, if "proc
             foo" called interact which then executed the  action
             inter_return,  proc  foo  would return.  (This means
             itself, first call interpreter (perhaps by using  an
             escape character), and then press ^Z.

             String-body  pairs  can  be  used as a shorthand for
             avoiding having to enter the interpreter and execute
             commands  interactively.  The previous terminal mode
             is used while the body  of  a  string-body  pair  is
             being executed.

             For  speed,  actions execute in raw mode by default.
             The -reset flag resets the terminal to the  mode  it
             had before interact was executed (invariably, cooked
             mode).  Note that characters entered when  the  mode
             is  being  switched may be lost (an unfortunate fea­
             ture of the terminal driver on some  systems).   The
             only  reason to use -reset is if your action depends
             on running in cooked mode.

             The -echo flag sends characters that match the  fol­
             lowing  pattern  back  to the process that generated
             them as each character is read.  This may be  useful
             when  the  user needs to see feedback from partially
             typed patterns.

             If a pattern is being echoed but eventually fails to
             match,  the  characters are sent to the spawned pro­
             cess.  If the spawned process then echoes them,  the
             user will see the characters twice.  -echo is proba­
             bly only appropriate in situations where the user is
             unlikely  to not complete the pattern.  For example,
             the following excerpt is from rftp,  the  recursive-
             ftp  script, where the user is prompted to enter ~g,
             ~p, or ~l, to get, put, or list the  current  direc­
             tory  recursively.   These  are so far away from the
             normal ftp commands, that the user  is  unlikely  to
             type ~ followed by anything else, except mistakenly,
             in which case,  they'll  probably  just  ignore  the
             result anyway.

                 interact {
                     -echo ~g {getcurdirectory 1}
                     -echo ~l {getcurdirectory 0}
                     -echo ~p {putcurdirectory}
                 }

             The  -nobuffer  flag sends characters that match the
             following pattern on to the output process as  char­
             acters are read.

             This  is  useful when you wish to let a program echo
             back the pattern.  For example, the following  might
             be  used  to  monitor  where  a person is dialing (a
             since it is presumed the user doesn't wish to inter­
             act blindly.

             The  -o  flag causes any following key-body pairs to
             be applied to the output  of  the  current  process.
             This  can  be useful, for example, when dealing with
             hosts that send unwanted characters during a  telnet
             session.

             By  default, interact expects the user to be writing
             stdin and  reading  stdout  of  the  Expect  process
             itself.   The  -u  flag  (for "user") makes interact
             look for the user as the process named by its  argu­
             ment (which must be a spawned id).

             This  allows  two  unrelated  processes to be joined
             together without using an explicit loop.  To aid  in
             debugging,  Expect  diagnostics  always go to stderr
             (or stdout for certain logging and debugging  infor­
             mation).   For the same reason, the interpreter com­
             mand will read interactively from stdin.

             For example, the following fragment creates a  login
             process.   Then  it  dials the user (not shown), and
             finally connects the two together.  Of  course,  any
             process  may be substituted for login.  A shell, for
             example, would allow the user to work  without  sup­
             plying an account and password.

                 spawn login
                 set login $spawn_id
                 spawn tip modem
                 # dial back out to user
                 # connect user to login
                 interact -u $login

             To  send  output  to  multiple  processes, list each
             spawn id list prefaced by a -output flag.  Input for
             a  group  of output spawn ids may be determined by a
             spawn id list prefaced  by  a  -input  flag.   (Both
             -input  and  -output may take lists in the same form
             as the -i flag in the expect  command,  except  that
             any_spawn_id  is  not  meaningful in interact.)  All
             following flags and strings (or patterns)  apply  to
             this input until another -input flag appears.  If no
             -input    appears,    -output    implies     "-input
             $user_spawn_id  -output".  (Similarly, with patterns
             that do not have -input.)  If one -input  is  speci­
             fied,  it  overrides  $user_spawn_id.   If  a second
             -input is specified, it overrides $spawn_id.   Addi­
             tional -input flags may be specified.

             specified with the -i, -u, -input, or -output flags.

       interpreter  [args]
             causes the user to  be  interactively  prompted  for
             Expect and Tcl commands.  The result of each command
             is printed.

             Actions such as break  and  continue  cause  control
             structures  (i.e., for, proc) to behave in the usual
             way.  However return causes interpreter to return to
             its caller, while inter_return causes interpreter to
             cause a return in its caller.  For example, if "proc
             foo"  called  interpreter  which  then  executed the
             action inter_return, proc  foo  would  return.   Any
             other command causes interpreter to continue prompt­
             ing for new commands.

             By default, the prompt contains two  integers.   The
             first  integer describes the depth of the evaluation
             stack  (i.e.,  how  many  times  Tcl_Eval  has  been
             called).   The  second  integer  is  the Tcl history
             identifier.  The prompt can be  set  by  defining  a
             procedure   called   "prompt1"  whose  return  value
             becomes the next prompt.  If a  statement  has  open
             quotes,  parens,  braces,  or  brackets, a secondary
             prompt (by default "+> ") is  issued  upon  newline.
             The secondary prompt may be set by defining a proce­
             dure called "prompt2".

             During interpreter, cooked mode is used, even if the
             its caller was using raw mode.

             If  stdin  is closed, interpreter will return unless
             the -eof flag is used, in which case the  subsequent
             argument is invoked.

       log_file [args] [[-a] file]
             If  a  filename  is provided, log_file will record a
             transcript of the session (beginning at that  point)
             in  the  file.   log_file  will stop recording if no
             argument is given.  Any previous log file is closed.

             Instead  of a filename, a Tcl file identifier may be
             provided by using the  -open  or  -leaveopen  flags.
             This  is  similar  to the spawn command.  (See spawn
             for more info.)

             The -a flag forces output to be logged that was sup­
             pressed by the log_user command.

             By  default,  the  log_file  command  appends to old
             files rather than truncating them,  for  the  conve­
             The -info flag causes log_user to return a  descrip­
             tion of the most recent non-info arguments given.

       match_max [-d] [-i spawn_id] [size]
             defines  the  size  of  the  buffer  (in bytes) used
             internally by expect.  With no  size  argument,  the
             current size is returned.

             With  the  -d  flag,  the default size is set.  (The
             initial default is 2000.)  With  the  -i  flag,  the
             size  is set for the named spawn id, otherwise it is
             set for the current process.

       overlay [-# spawn_id] [-# spawn_id] [...] program [args]
             executes program args in place of the current Expect
             program,  which  terminates.  A bare hyphen argument
             forces a hyphen in front of the command name  as  if
             it  was  a  login  shell.   All spawn_ids are closed
             except for those  named  as  arguments.   These  are
             mapped onto the named file identifiers.

             Spawn_ids are mapped to file identifiers for the new
             program to inherit.  For example, the following line
             runs  chess  and  allows  it to be controlled by the
             current process - say, a chess master.

                 overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess

             This is more efficient than "interact -u",  however,
             it  sacrifices the ability to do programmed interac­
             tion since the Expect process is no longer  in  con­
             trol.

             Note  that  no  controlling  terminal  is  provided.
             Thus, if you disconnect  or  remap  standard  input,
             programs  that  do  job control (shells, login, etc)
             will not function properly.

       parity [-d] [-i spawn_id] [value]
             defines  whether  parity  should  be   retained   or
             stripped  from  the output of spawned processes.  If
             value is zero, parity is stripped, otherwise  it  is
             not  stripped.   With no value argument, the current
             value is returned.

             With the -d flag, the default parity value  is  set.
             (The  initial  default  is  1,  i.e.,  parity is not
             stripped.)  With the -i flag, the  parity  value  is
             set  for the named spawn id, otherwise it is set for
             the current process.

       remove_nulls [-d] [-i spawn_id] [value]
             null bytes to the log and stdout.

       send [-flags] string
             Sends string to the current process.   For  example,
             the command

                 send "hello world\r"

             sends  the  characters,  h e l l o <blank> w o r l d
             <return> to the current process.   (Tcl  includes  a
             printf-like  command (called format) which can build
             arbitrarily complex strings.)

             Characters are sent  immediately  although  programs
             with  line-buffered  input will not read the charac­
             ters until a return character  is  sent.   A  return
             character is denoted "\r".

             The  --  flag  forces the next argument to be inter­
             preted as a string rather than a flag.   Any  string
             can  be  preceded by "--" whether or not it actually
             looks like a flag.  This provides a reliable  mecha­
             nism  to  specify  variable  strings  without  being
             tripped up by  those  that  accidentally  look  like
             flags.   (All strings starting with "-" are reserved
             for future options.)

             The -i flag declares that the string be sent to  the
             named  spawn_id.   If the spawn_id is user_spawn_id,
             and the terminal is in raw  mode,  newlines  in  the
             string are translated to return-newline sequences so
             that they appear as if the terminal  was  in  cooked
             mode.  The -raw flag disables this translation.

             The  -null flag sends null characters (0 bytes).  By
             default, one null is sent.  An  integer  may  follow
             the -null to indicate how many nulls to send.

             The  -break  flag generates a break condition.  This
             only makes sense if the spawn id  refers  to  a  tty
             device  opened  via  "spawn  -open".   If  you  have
             spawned a process such as tip, you should use  tip's
             convention for generating a break.

             The  -s flag forces output to be sent "slowly", thus
             avoid the common situation where a computer outtypes
             an  input  buffer  that was designed for a human who
             would never outtype the same buffer.  This output is
             controlled  by the value of the variable "send_slow"
             which takes a two element list.  The  first  element
             is  an integer that describes the number of bytes to
             send atomically.  The second element is a real  num­
             seconds.   The first is used by default.  The second
             is used at word  endings,  to  simulate  the  subtle
             pauses  that occasionally occur at such transitions.
             The third parameter  is  a  measure  of  variability
             where  .1  is  quite variable, 1 is reasonably vari­
             able, and 10 is quite invariable.  The extremes  are
             0 to infinity.  The last two parameters are, respec­
             tively, a minimum  and  maximum  interarrival  time.
             The minimum and maximum are used last and "clip" the
             final time.  The ultimate average can be quite  dif­
             ferent  from  the  given  average if the minimum and
             maximum clip enough values.

             As an example, the following command emulates a fast
             and consistent typist:

                 set send_human {.1 .3 1 .05 2}
                 send -h "I'm hungry.  Let's do lunch."

             while  the  following might be more suitable after a
             hangover:

                 set send_human {.4 .4 .2 .5 100}
                 send -h "Goodd party lash night!"

             Note that errors are not simulated, although you can
             set  up  error  correction  situations  yourself  by
             embedding mistakes and corrections in a  send  argu­
             ment.

             The  flags  for sending null characters, for sending
             breaks, for forcing slow output and for  human-style
             output  are  mutually exclusive. Only the one speci­
             fied last will be used. Furthermore, no string argu­
             ment  can  be  specified  with the flags for sending
             null characters or breaks.

             It is a good idea to precede the  first  send  to  a
             process by an expect.  expect will wait for the pro­
             cess to start, while send cannot.  In particular, if
             the  first  send completes before the process starts
             running, you  run  the  risk  of  having  your  data
             ignored.   In  situations where interactive programs
             offer no initial prompt, you can precede send  by  a
             delay as in:

                 # To avoid giving hackers hints on how to break in,
                 # this system does not prompt for an external password.
                 # Wait for 5 seconds for exec to complete
                 spawn telnet very.secure.gov
                 sleep 5
                 send password\r

             the log file  (see  log_file.)   The  arguments  are
             ignored if no log file is open.

       send_tty [-flags] string
             is  like  send,  except  that  the output is sent to
             /dev/tty rather than the current process.

       send_user [-flags] string
             is like send, except that the output is sent to std­
             out rather than the current process.

       sleep seconds
             causes  the  script to sleep for the given number of
             seconds.  Seconds may be a decimal  number.   Inter­
             rupts  (and  Tk events if you are using Expectk) are
             processed while Expect sleeps.

       spawn [args] program [args]
             creates a new process  running  program  args.   Its
             stdin, stdout and stderr are connected to Expect, so
             that they may be read and written  by  other  Expect
             commands.   The  connection is broken by close or if
             the process itself closes any of  the  file  identi­
             fiers.

             When  a  process  is  started by spawn, the variable
             spawn_id is set to a descriptor  referring  to  that
             process.   The process described by spawn_id is con­
             sidered the current process.  spawn_id may  be  read
             or written, in effect providing job control.

             user_spawn_id  is  a  global  variable  containing a
             descriptor which refers to the user.   For  example,
             when  spawn_id  is set to this value, expect behaves
             like expect_user.

             error_spawn_id is a  global  variable  containing  a
             descriptor  which refers to the standard error.  For
             example, when spawn_id is set to  this  value,  send
             behaves like send_error.

             tty_spawn_id  is  a  global  variable  containing  a
             descriptor which refers to  /dev/tty.   If  /dev/tty
             does  not  exist  (such  as  in a cron, at, or batch
             script), then tty_spawn_id is not defined.  This may
             be tested as:

                 if {[info vars tty_spawn_id]} {
                     # /dev/tty exists
                 } else {
                     # /dev/tty doesn't exist
                     # probably in cron, batch, or at script

             ported on all systems.

             Internally, spawn uses a pty, initialized  the  same
             way  as the user's tty.  This is further initialized
             so  that  all  settings  are  "sane"  (according  to
             stty(1)).   If the variable stty_init is defined, it
             is interpreted in the style  of  stty  arguments  as
             further  configuration.  For example, "set stty_init
             raw" will cause further spawned  processes's  termi­
             nals  to  start  in  raw mode.  -nottycopy skips the
             initialization based on the user's tty.   -nottyinit
             skips the "sane" initialization.

             Normally,  spawn  takes  little time to execute.  If
             you notice spawn  taking  a  significant  amount  of
             time,  it  is  probably  encountering  ptys that are
             wedged.  A number of tests are run on ptys to  avoid
             entanglements with errant processes.  (These take 10
             seconds per wedged pty.)  Running Expect with the -d
             option will show if Expect is encountering many ptys
             in odd states.  If you cannot kill the processes  to
             which  these  ptys  are attached, your only recourse
             may be to reboot.

             If program cannot be  spawned  successfully  because
             exec(2)  fails (e.g. when program doesn't exist), an
             error message will be returned by the next  interact
             or expect command as if program had run and produced
             the error message as output.   This  behavior  is  a
             natural  consequence of the implementation of spawn.
             Internally, spawn forks,  after  which  the  spawned
             process  has no way to communicate with the original
             Expect  process  except  by  communication  via  the
             spawn_id.

             The -open flag causes the next argument to be inter­
             preted as a Tcl file identifier (i.e.,  returned  by
             open.)   The spawn id can then be used as if it were
             a spawned process.  (The file identifier  should  no
             longer  be  used.)  This lets you treat raw devices,
             files, and pipelines as  spawned  processes  without
             using  a pty.  0 is returned to indicate there is no
             associated process.   When  the  connection  to  the
             spawned  process is closed, so is the Tcl file iden­
             tifier.  The -leaveopen flag  is  similar  to  -open
             except that -leaveopen causes the file identifier to
             be left open even after the spawn id is closed.

             The -pty flag causes a pty to be opened but no  pro­
             cess spawned.  0 is returned to indicate there is no
             associated process.  Spawn_id is set as usual.

             runs  Expect  while  tracing  the  first 4 levels of
             calls, but none below that.

                 expect -c "strace 4" script.exp

             The -info flag causes strace to return a description
             of the most recent non-info arguments given.

       stty args
             changes  terminal  modes  similarly  to the external
             stty command.

             By default, the controlling  terminal  is  accessed.
             Other  terminals  can  be  accessed  by appending "<
             /dev/tty..." to the command.  (Note that  the  argu­
             ments should not be grouped into a single argument.)

             Requests for status return it as the result  of  the
             command.  If no status is requested and the control­
             ling terminal is accessed, the  previous  status  of
             the  raw  and echo attributes are returned in a form
             which can later be used by the command.

             For example, the arguments raw or  -cooked  put  the
             terminal  into  raw  mode.   The  arguments  -raw or
             cooked put the terminal into cooked mode.  The argu­
             ments  echo and -echo put the terminal into echo and
             noecho mode respectively.

             The following example illustrates how to temporarily
             disable  echoing.   This could be used in otherwise-
             automatic scripts to avoid  embedding  passwords  in
             them.   (See  more  discussion  on this under EXPECT
             HINTS below.)

                 stty -echo
                 send_user "Password: "
                 expect_user -re "(.*)\n"
                 set password $expect_out(1,string)
                 stty echo

       system args
             gives args to sh(1) as input, just as if it had been
             typed  as  a  command from a terminal.  Expect waits
             until the shell terminates.  The return status  from
             sh  is  handled  the  same way that exec handles its
             return status.

             In contrast to exec which redirects stdin and stdout
             to the script, system performs no redirection (other
                 %a      abbreviated weekday name
                 %A      full weekday name
                 %b      abbreviated month name
                 %B      full month name
                 %c      date-time as in: Wed Oct  6 11:45:56 1993
                 %d      day of the month (01-31)
                 %H      hour (00-23)
                 %I      hour (01-12)
                 %j      day (001-366)
                 %m      month (01-12)
                 %M      minute (00-59)
                 %p      am or pm
                 %S      second (00-61)
                 %u      day (1-7, Monday is first day of week)
                 %U      week (00-53, first Sunday is first day of week one)
                 %V      week (01-53, ISO 8601 style)
                 %w      day (0-6)
                 %W      week (00-53, first Monday is first day of week one)
                 %x      date-time as in: Wed Oct  6 1993
                 %X      time as in: 23:59:59
                 %y      year (00-99)
                 %Y      year as in: 1993
                 %Z      timezone (or nothing if not determinable)
                 %%      a bare percent sign

             Other % specifications are undefined.  Other charac­
             ters  will  be passed through untouched.  Only the C
             locale is supported.

             The -seconds flag introduces  a  number  of  seconds
             since the epoch to be used as a source from which to
             format.  Otherwise, the current time is used.

             The -gmt flag forces timestamp output to use the GMT
             timezone.  With no flag, the local timezone is used.

       trap [[command] signals]
             causes the given command to be executed upon  future
             receipt of any of the given signals.  The command is
             executed in the global scope.  If command is absent,
             the  signal  action  is returned.  If command is the
             string SIG_IGN, the signals are ignored.  If command
             is the string SIG_DFL, the signals are result to the
             system default.  signals is either a  single  signal
             or  a  list  of  signals.   Signals may be specified
             numerically or symbolically as per  signal(3).   The
             "SIG" prefix may be omitted.

             With  no  arguments  (or the argument -number), trap
             returns the signal number of the trap  command  cur­
             rently being executed.

             largest signal number that can be set.

             For  example,  the command "trap {send_user "Ouch!"}
             SIGINT" will  print  "Ouch!"   each  time  the  user
             presses ^C.

             By  default,  SIGINT (which can usually be generated
             by pressing ^C) and SIGTERM cause  Expect  to  exit.
             This  is  due  to  the  following  trap,  created by
             default when Expect starts.

                 trap exit {SIGINT SIGTERM}

             If you use the -D flag to start the debugger, SIGINT
             is  redefined  to  start  the  interactive debugger.
             This is due to the following trap:

                 trap {exp_debug 1} SIGINT

             The debugger trap can  be  changed  by  setting  the
             environment variable EXPECT_DEBUG_INIT to a new trap
             command.

             You can, of course, override both of these  just  by
             adding trap commands to your script.  In particular,
             if you have your own "trap exit SIGINT",  this  will
             override  the  debugger trap.  This is useful if you
             want to prevent users from getting to  the  debugger
             at all.

             If  you  want  to define your own trap on SIGINT but
             still trap to the debugger when it is running, use:

                 if {![exp_debug]} {trap mystuff SIGINT}

             Alternatively, you can trap to  the  debugger  using
             some other signal.

             trap  will  not  let  you  override  the  action for
             SIGALRM as this is used internally to  Expect.   The
             disconnect command sets SIGALRM to SIG_IGN (ignore).
             You can reenable this as long as you disable it dur­
             ing subsequent spawn commands.

             See signal(3) for more info.

       wait [args]
             delays  until a spawned process (or the current pro­
             cess if none is named) terminates.

             wait normally returns a list of four integers.   The
             first  integer  is  the  pid of the process that was
             signal name and a short textual description.

             The -i flag declares the process to wait correspond­
             ing  to  the  named  spawn_id  (NOT the process id).
             Inside a SIGCHLD handler, it is possible to wait for
             any spawned process by using the spawn id -1.

             The  -nowait  flag causes the wait to return immedi­
             ately with the  indication  of  a  successful  wait.
             When  the  process  exits (later), it will automati­
             cally disappear without the  need  for  an  explicit
             wait.

             The  wait command may also be used wait for a forked
             process using the arguments "-i -1".  Unlike its use
             with spawned processes, this command can be executed
             at any time.  There is no control over which process
             is reaped.  However, the return value can be checked
             for the process id.


LIBRARIES

       Expect automatically knows about  two  built-in  libraries
       for  Expect scripts.  These are defined by the directories
       named in the variables exp_library  and  exp_exec_library.
       Both  are  meant to contain utility files that can be used
       by other scripts.

       exp_library   contains   architecture-independent   files.
       exp_exec_library  contains  architecture-dependent  files.
       Depending on your system, both directories may be  totally
       empty.   The  existence of the file $exp_exec_library/cat-
       buffers  describes  whether  your  /bin/cat   buffers   by
       default.


PRETTY-PRINTING

       A  vgrind  definition  is  available  for  pretty-printing
       Expect scripts.  Assuming the vgrind  definition  supplied
       with  the  Expect distribution is correctly installed, you
       can use it as:

           vgrind -lexpect file


EXAMPLES

       It many not be apparent how  to  put  everything  together
       that  the man page describes.  I encourage you to read and
       try out the examples  in  the  example  directory  of  the
       Expect  distribution.   Some  of  them  are real programs.
       Others are simply illustrative of certain techniques,  and
       of  course,  a  couple  are just quick hacks.  The INSTALL
       file has a quick overview of these programs.

       Expect takes a rather liberal view of scoping.  In partic­
       ular, variables read by commands specific  to  the  Expect
       program  will be sought first from the local scope, and if
       not found, in the global scope.  For example,  this  obvi­
       ates the need to place "global timeout" in every procedure
       you write that uses expect.  On the other hand,  variables
       written  are  always in the local scope (unless a "global"
       command has been issued).  The most  common  problem  this
       causes  is when spawn is executed in a procedure.  Outside
       the procedure, spawn_id no longer exists, so  the  spawned
       process is no longer accessible simply because of scoping.
       Add a "global spawn_id" to such a procedure.

       If you cannot enable the multispawning  capability  (i.e.,
       your  system  supports  neither  select  (BSD  *.*),  poll
       (SVR>2), nor something equivalent), Expect  will  only  be
       able to control a single process at a time.  In this case,
       do not attempt to set spawn_id,  nor  should  you  execute
       processes  via  exec  while  a spawned process is running.
       Furthermore, you will not be able to expect from  multiple
       processes (including the user as one) at the same time.

       Terminal parameters can have a big effect on scripts.  For
       example, if a script is written to look  for  echoing,  it
       will misbehave if echoing is turned off.  For this reason,
       Expect forces sane terminal parameters by default.  Unfor­
       tunately,  this  can make things unpleasant for other pro­
       grams.  As an example, the emacs shell wants to change the
       "usual"  mappings: newlines get mapped to newlines instead
       of carriage-return  newlines,  and  echoing  is  disabled.
       This  allows  one  to  use  emacs  to edit the input line.
       Unfortunately, Expect cannot possibly guess this.

       You can request that Expect not override its default  set­
       ting  of  terminal  parameters,  but you must then be very
       careful when writing scripts for  such  environments.   In
       the  case of emacs, avoid depending upon things like echo­
       ing and end-of-line mappings.

       The commands that accepted arguments braced into a  single
       list (the expect variants and interact) use a heuristic to
       decide if the list is actually one argument or many.   The
       heuristic can fail only in the case when the list actually
       does represent a single argument which has multiple embed­
       ded  \n's  with  non-whitespace  characters  between them.
       This seems sufficiently improbable, however  the  argument
       "-nobrace"  can  be  used to force a single argument to be
       handled as a single argument.  This could  conceivably  be
       used with machine-generated Expect code.


BUGS

       allocate ptys  if  you  define  a  SIGCHLD  handler.   See
       grantpt page for more info.

       IRIX 6.0 does not handle pty permissions correctly so that
       if Expect attempts to allocate a pty  previously  used  by
       someone else, it fails.  Upgrade to IRIX 6.1.

       Telnet  (verified only under SunOS 4.1.2) hangs if TERM is
       not set.  This is a problem under  cron,  at  and  in  cgi
       scripts,  which do not define TERM.  Thus, you must set it
       explicitly - to what type is usually irrelevant.  It  just
       has  to  be set to something!  The following probably suf­
       fices for most cases.

           set env(TERM) vt100

       Tip (verified only under BSDI BSD/OS 3.1  i386)  hangs  if
       SHELL and HOME are not set.  This is a problem under cron,
       at and in cgi scripts, which do not define these  environ­
       ment  variables.   Thus, you must set them explicitly - to
       what type is usually irrelevant.  It just has to be set to
       something!   The  following  probably  suffices  for  most
       cases.

           set env(SHELL) /bin/sh
           set env(HOME) /usr/local/bin

       Some implementations of ptys are designed so that the ker­
       nel  throws  away any unread output after 10 to 15 seconds
       (actual number is implementation-dependent) after the pro­
       cess has closed the file descriptor.  Thus Expect programs
       such as

           spawn date
           sleep 20
           expect

       will fail.  To avoid this, invoke non-interactive programs
       with  exec  rather  than spawn.  While such situations are
       conceivable, in practice I have never encountered a situa­
       tion in which the final output of a truly interactive pro­
       gram would be lost due to this behavior.

       On the other hand, Cray UNICOS ptys throw away any  unread
       output  immediately  after the process has closed the file
       descriptor.  I have reported this to  Cray  and  they  are
       working on a fix.

       Sometimes  a  delay  is  required  between  a prompt and a

       trap  -code  will  not  work with any command that sits in
       Tcl's event loop, such as sleep.  The problem is  that  in
       the  event  loop, Tcl discards the return codes from async
       event handlers.  A workaround is to set a flag in the trap
       code.   Then  check the flag immediately after the command
       (i.e., sleep).


EXPECT HINTS

       There are a couple of things about Expect that may be non-
       intuitive.  This section attempts to address some of these
       things with a couple of suggestions.

       A common expect problem is how to recognize shell prompts.
       Since these are customized differently by differently peo­
       ple and different shells, portably automating  rlogin  can
       be  difficult  without  knowing  the prompt.  A reasonable
       convention is to have users  store  a  regular  expression
       describing  their prompt (in particular, the end of it) in
       the environment variable  EXPECT_PROMPT.   Code  like  the
       following  can  be  used.  If EXPECT_PROMPT doesn't exist,
       the code still has a good chance of functioning correctly.

           set prompt "(%|#|\\$) $"          ;# default prompt
           catch {set prompt $env(EXPECT_PROMPT)}

           expect -re $prompt

       I  encourage you to write expect patterns that include the
       end of whatever you expect to see.  This avoids the possi­
       bility  of  answering  a question before seeing the entire
       thing.  In addition, while you may well be able to  answer
       questions  before  seeing  them  entirely,  if  you answer
       early,  your answer may appear echoed back in  the  middle
       of  the  question.  In other words, the resulting dialogue
       will be correct but look scrambled.

       Most prompts include a space character at  the  end.   For
       example,  the  prompt  from  ftp is 'f', 't', 'p', '>' and
       <blank>.  To match this prompt, you must account for  each
       of  these  characters.   It  is  a  common  mistake not to
       include the blank.  Put the blank in explicitly.

       If you use a pattern of the form X*, the * will match  all
       the  output  received  from the end of X to the last thing
       received.  This sounds intuitive but can be somewhat  con­
       fusing  because  the phrase "last thing received" can vary
       depending upon the speed of the computer and the  process­
       ing of I/O both by the kernel and the device driver.

       In  particular, humans tend to see program output arriving
       Thus, if you can express the  last  few  characters  of  a
       prompt when writing patterns, it is wise to do so.

       If  you  are waiting for a pattern in the last output of a
       program and the program emits something else instead,  you
       will  not be able to detect that with the timeout keyword.
       The reason is that expect will not timeout  -  instead  it
       will  get an eof indication.  Use that instead.  Even bet­
       ter, use both.  That  way  if  that  line  is  ever  moved
       around, you won't have to edit the line itself.

       Newlines  are  usually converted to carriage return, line­
       feed sequences when output by the terminal driver.   Thus,
       if  you  want  a  pattern  that explicitly matches the two
       lines, from, say, printf("foo\nbar"), you should  use  the
       pattern "foo\r\nbar".

       A  similar  translation occurs when reading from the user,
       via expect_user.  In this case, when you press return,  it
       will  be  translated  to a newline.  If Expect then passes
       that to a program which sets  its  terminal  to  raw  mode
       (like telnet), there is going to be a problem, as the pro­
       gram expects a true return.  (Some programs  are  actually
       forgiving  in  that they will automatically translate new­
       lines to returns, but most don't.)   Unfortunately,  there
       is no way to find out that a program put its terminal into
       raw mode.

       Rather than manually replacing newlines with returns,  the
       solution is to use the command "stty raw", which will stop
       the translation.  Note, however, that this means that  you
       will no longer get the cooked line-editing features.

       interact implicitly sets your terminal to raw mode so this
       problem will not arise then.

       It is often useful to store passwords  (or  other  private
       information)  in  Expect scripts.  This is not recommended
       since anything that is stored on a computer is susceptible
       to  being accessed by anyone.  Thus, interactively prompt­
       ing for passwords from a script is  a  smarter  idea  than
       embedding  them  literally.   Nonetheless,  sometimes such
       embedding is the only possibility.

       Unfortunately, the UNIX file system has no direct  way  of
       creating  scripts  which  are  executable  but unreadable.
       Systems which support setgid shell scripts may  indirectly
       simulate this as follows:

       Create  the  Expect script (that contains the secret data)
       as usual.  Make its permissions be  750  (-rwxr-x---)  and
       owned  by  a trusted group, i.e., a group which is allowed
       Conference, Anaheim, California, June 11-15, 1990.
       "Using  expect to Automate System Administration Tasks" by
       Don Libes, Proceedings of the 1990 USENIX Large  Installa­
       tion  Systems Administration Conference, Colorado Springs,
       Colorado, October 17-19, 1990.
       "Tcl: An Embeddable Command Language" by John  Ousterhout,
       Proceedings of the Winter 1990 USENIX Conference, Washing­
       ton, D.C., January 22-26, 1990.
       "expect: Scripts for Controlling Interactive Programs"  by
       Don Libes, Computing Systems, Vol. 4, No. 2, University of
       California Press Journals, November 1991.
       "Regression Testing and  Conformance  Testing  Interactive
       Programs",  by  Don  Libes, Proceedings of the Summer 1992
       USENIX Conference, pp.  135-144,  San  Antonio,  TX,  June
       12-15, 1992.
       "Kibitz   -   Connecting   Multiple  Interactive  Programs
       Together", by Don Libes, Software - Practice & Experience,
       John  Wiley  & Sons, West Sussex, England, Vol. 23, No. 5,
       May, 1993.
       "A Debugger for Tcl Applications", by Don Libes,  Proceed­
       ings  of  the  1993  Tcl/Tk  Workshop,  Berkeley, CA, June
       10-11, 1993.


AUTHOR

       Don Libes, National Institute of Standards and Technology


ACKNOWLEDGMENTS

       Thanks to John Ousterhout for Tcl, and Scott  Paisley  for
       inspiration.   Thanks  to Rob Savoye for Expect's autocon­
       figuration code.

       The HISTORY  file  documents  much  of  the  evolution  of
       expect.   It  makes interesting reading and might give you
       further insight to this software.  Thanks  to  the  people
       mentioned  in  it  who  sent  me  bug fixes and gave other
       assistance.

       Design and implementation of Expect was paid for  in  part
       by  the  U.S.  government  and  is therefore in the public
       domain.  However the author and NIST would like credit  if
       this  program  and  documentation  or portions of them are
       used.

                         29 December 1994               EXPECT(1)
  

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