LIBEXPECT(3)                                         LIBEXPECT(3)

       libexpect  - programmed dialogue with interactive programs
       - C functions

       This library contains functions that allow  Expect  to  be
       used  as  a Tcl extension or to be used directly from C or
       C++ (without Tcl).  Adding Expect as a  Tcl  extension  is
       very short and simple, so that will be covered first.

       #include expect_tcl.h

       cc files... -lexpect5.20 -ltcl7.5 -lm

       Note: library versions may differ in the actual release.

       The Expect_Init function adds expect commands to the named
       interpreter.  It avoids overwriting commands that  already
       exist,  however  aliases  beginning with "exp_" are always
       created for expect commands.  So for example,  "send"  can
       be used as "exp_send".

       Generally,  you  should  only  call  Expect  commands  via
       Tcl_Eval.   Certain  auxiliary  functions  may  be  called
       directly.   They are summarized below.  They may be useful
       in  constructing  your  own  main.   Look  at   the   file
       exp_main_exp.c  in  the Expect distribution as a prototype
       main.  Another prototype is tclAppInit.c in the Tcl source
       distribution.   A  prototype  for  working  with  Tk is in
       exp_main_tk.c in the Expect distribution.

       int exp_cmdlinecmds;
       int exp_interactive;
       FILE *exp_cmdfile;
       char *exp_cmdfilename;
       int exp_tcl_debugger_available;

       void exp_parse_argv(Tcl_Interp *,int argc,char **argv);
       int  exp_interpreter(Tcl_Interp *);
       void exp_interpret_cmdfile(Tcl_Interp *,FILE *);
       void exp_interpret_cmdfilename(Tcl_Interp *,char *);
       void exp_interpret_rcfiles(Tcl_Interp *,int my_rc,int sys_rc);
       char *    exp_cook(char *s,int *len);
       void (*exp_app_exit)EXP_PROTO((Tcl_Interp *);
       void exp_exit(Tcl_Interp *,int status);
       void exp_exit_handlers(Tcl_Interp *);
       void exp_error(Tcl_Interp,char *,...);

       exp_cmdlinecmds is 1 if Expect has been invoked with  com-
       mands  on  the  program command-line (using "-c" for exam-
       ple).  exp_interactive is 1 if  Expect  has  been  invoked
       with  the  -i  flag  or  if no commands or script is being
       invoked.  exp_cmdfile is a stream from which  Expect  will
       read  commands.   exp_cmdfilename  is  the  name of a file
       which  Expect  will   open   and   read   commands   from.
       exp_tcl_debugger_available  is  1 if the debugger has been

       exp_parse_argv reads the  representation  of  the  command
       line.   Based on what is found, any of the other variables
       listed here  are  initialized  appropriately.   exp_inter-
       preter  interactively  prompts  the  user for commands and
       evaluates them.   exp_interpret_cmdfile  reads  the  given
       stream  and  evaluates  any  commands  found.   exp_inter-
       pret_cmdfilename opens the named file  and  evaluates  any
       commands  found.  exp_interpret_rcfiles reads and evalutes
       the .rc files.  If my_rc  is  zero,  then  ~/.expectrc  is
       skipped.  If sys_rc is zero, then the system-wide expectrc
       file is skipped.  exp_cook returns a  static  buffer  con-
       taining  the argument reproduced with newlines replaced by
       carriage-return linefeed sequences.  The  primary  purpose
       of this is to allow messages to be produced without worry-
       ing about whether the terminal is in raw  mode  or  cooked
       mode.   If  length  is  zero,  it  is computed via strlen.
       exp_error is a printf-like function that writes the result
       to interp->result.

       #include <expect.h>

       exp_spawnl(file, arg0 [, arg1, ..., argn] (char *)0);
       char *file;
       char *arg0, *arg1, ... *argn;

       char *file, *argv[ ];

       int fd;

       FILE *
       char *command;

       extern int exp_pid;
       extern int exp_ttyinit;
       extern int exp_ttycopy;
       extern int exp_console;
       extern char *exp_stty_init;
       extern void (*exp_close_in_child)();
       extern void (*exp_child_exec_prelude)();
       extern void exp_close_tcl_files();

       cc files... -lexpect -ltcl -lm

       exp_spawnl  and  exp_spawnv fork a new process so that its
       stdin, stdout, and stderr can be written and read  by  the
       current  process.   file  is the name of a file to be exe-
       cuted.  The  arg  pointers  are  null-terminated  strings.
       Following the style of execve(), arg0 (or argv[0]) is cus-
       tomarily a duplicate of the name of the file.

       Four interfaces are available, exp_spawnl is  useful  when
       the   number  of  arguments  is  known  at  compile  time.
       exp_spawnv is useful when the number of arguments  is  not
       known at compile time.  exp_spawnfd is useful when an open
       file  descriptor  is  already  available  as   a   source.
       exp_popen is explained later on.

       If  the process is successfully created, a file descriptor
       is returned which corresponds to the process's stdin, std-
       out  and stderr.  A stream may be associated with the file
       descriptor by using fdopen().  (This  should  almost  cer-
       tainly be followed by setbuf() to unbuffer the I/O.)

       Closing  the file descriptor will typically be detected by
       the process as an EOF.  Once  such  a  process  exits,  it
       should  be  waited upon (via wait) in order to free up the
       kernel process slot.  (Some systems  allow  you  to  avoid
       this if you ignore the SIGCHLD signal).

       exp_popen  is yet another interface, styled after popen().
       It takes a Bourne shell command line, and returns a stream
       that  corresponds  to  the  process's  stdin,  stdout  and
       stderr.  The  actual  implementation  of  exp_popen  below
       demonstrates exp_spawnl.

       FILE *
       char *program;
            FILE *fp;
            int ec;

            if (0 > (ec = exp_spawnl("sh","sh","-c",program,(char *)0)))
            if (NULL == (fp = fdopen(ec,"r+")) return(0);
            setbuf(fp,(char *)0);

       After a process is started, the variable exp_pid is set to
       the  process-id  of  the  new   process.    The   variable
       exp_pty_slave_name is set to the name of the slave side of
       the pty.

       The spawn functions uses a pty  to  communicate  with  the
       process.   By default, the pty is initialized the same way
       as the user's tty (if possible, i.e., if  the  environment
       has  a  controlling terminal.)  This initialization can be
       skipped by setting exp_ttycopy to 0.

       The  pty  is  further  initialized  to  some  system  wide
       defaults  if exp_ttyinit is non-zero.  The default is gen-
       erally comparable to "stty sane".

       The tty setting can be further  modified  by  setting  the
       variable  exp_stty_init.   This variable is interpreted in
       the style of stty arguments.  For example, exp_stty_init =
       "sane"; repeats the default initialization.

       On some systems, it is possible to redirect console output
       to ptys.  If this is supported, you  can  force  the  next
       spawn to obtain the console output by setting the variable
       exp_console to 1.

       Between the time a process is started and the new  program
       is  given  control,  the  spawn functions can clean up the
       environment by closing file descriptors.  By default,  the
       only  file  descriptors closed are ones internal to Expect
       and any marked "close-on-exec".

       If needed, you can close additional  file  descriptors  by
       creating  an  appropriate  function  and  assigning  it to
       exp_close_in_child.  The function will be called after the
       fork  and before the exec.  (This also modifies the behav-
       ior of the spawn command in Expect.)

       If you are also using Tcl, it may be convenient to use the
       function   exp_close_tcl_files   which  closes  all  files
       between the default  standard  file  descriptors  and  the
       highest descriptor known to Tcl.  (Expect does this.)

       The  function  exp_child_exec_prelude is the last function
       called prior to the actual exec in  the  child.   You  can
       redefine  this for effects such as manipulating the uid or
       the signals.

       extern int exp_autoallocpty;
       extern int exp_pty[2];

       The spawn functions use a pty to communicate with the pro-
       cess.   By  default, a pty is automatically allocated each
       time a process is spawned.  If you want to  allocate  ptys
       yourself,  before  calling one of the spawn functions, set
       exp_autoallocpty to 0, exp_pty[0] to the master  pty  file
       descriptor  and  exp_pty[1] to the slave pty file descrip-
       tor.  The expect library will not do any  pty  initializa-
       tions  (e.g.,  exp_stty_init will not be used).  The slave
       pty file descriptor will be automatically closed when  the
       process  is  spawned.   After  the process is started, all
       further communication takes place with the master pty file

       exp_spawnl and exp_spawnv duplicate the shell's actions in
       searching for an executable file in a list of directories.
       The directory list is obtained from the environment.

       While  it  is  possible  to use read() to read information
       from a process spawned by exp_spawnl or  exp_spawnv,  more
       convenient functions are provided.  They are as follows:

       int fd;
       enum exp_type type;
       char *pattern1, *pattern2, ...;
       regexp *re1, *re2, ...;
       int value1, value2, ...;

       FILE *fp;
       enum exp_type type;
       char *pattern1, *pattern2, ...;
       regexp *re1, *re2, ...;
       int value1, value2, ...;

       enum exp_type {

       struct exp_case {
       char *pattern;
       regexp *re;
       enum exp_type type;
       int value;

       int fd;
       struct exp_case *cases;

       FILE *fp;
       struct exp_case *cases;

       extern int exp_timeout;
       extern char *exp_match;
       extern char *exp_match_end;
       extern char *exp_buffer;
       extern char *exp_buffer_end;
       extern int exp_match_max;
       extern int exp_full_buffer;
       extern int exp_remove_nulls;

       The functions wait until the output from a process matches
       one of the patterns, a specified time period  has  passed,
       or an EOF is seen.

       The  first  argument  to  each  function  is either a file
       descriptor or a  stream.   Successive  sets  of  arguments
       describe  patterns and associated integer values to return
       when the pattern matches.

       The type argument is one of four  values.   exp_end  indi-
       cates  that  no  more patterns appear.  exp_glob indicates
       that  the  pattern  is  a   glob-style   string   pattern.
       exp_exact  indicates  that the pattern is an exact string.
       exp_regexp indicates that the pattern  is  a  regexp-style
       string  pattern.   exp_compiled indicates that the pattern
       is a regexp-style string pattern, and  that  its  compiled
       form  is  also provided.  exp_null indicates that the pat-
       tern is a null (for debugging purposes, a  string  pattern
       must also follow).

       If  the  compiled  form is not provided with the functions
       exp_expectl and exp_fexpectl, any pattern compilation done
       internally is thrown away after the function returns.  The
       functions exp_expectv and exp_fexpectv will  automatically
       compile  patterns  and will not throw them away.  Instead,
       they must be discarded by the user,  by  calling  free  on
       each  pattern.   It is only necessary to discard them, the
       last time the cases are used.

       Regexp subpatterns matched are stored in the compiled reg-
       exp.   Assuming  "re"  contains  a  compiled  regexp,  the
       matched string can be found in re->startp[0].   The  match
       substrings  (according to the parentheses) in the original
       pattern can be found in re->startp[1], re->startp[2],  and
       so  on,  up  to  re->startp[9].  The corresponding strings
       ends are re->endp[x] where x is that same index as for the
       string start.

       The  type exp_null matches if a null appears in the input.
       The variable exp_remove_nulls must be set to 0 to  prevent
       nulls  from  being  automatically  stripped.   By default,
       exp_remove_nulls is set to 1 and nulls  are  automatically

       exp_expectv and exp_fexpectv are useful when the number of
       patterns is not known in advance.  In this case, the  sets
       are provided in an array.  The end of the array is denoted
       by a struct exp_case with type exp_end.  For the  rest  of
       this  discussion,  these  functions  will  be  referred to
       generically as expect.

       If a pattern matches, then the corresponding integer value
       is  returned.   Values  need  not  be unique, however they
       should be positive to avoid being  mistaken  for  EXP_EOF,
       EXP_TIMEOUT,  or EXP_FULLBUFFER.  Upon EOF or timeout, the
       value EXP_EOF or EXP_TIMEOUT  is  returned.   The  default
       timeout period is 10 seconds but may be changed by setting
       the variable exp_timeout.  A value of -1 disables a  time-
       out  from occurring.  A value of 0 causes the expect func-
       tion to return immediately (i.e., poll) after one  read().
       However  it must be preceded by a function such as select,
       poll, or an event manager callback to guarantee that there
       is data to be read.

       If  the variable exp_full_buffer is 1, then EXP_FULLBUFFER
       is returned if exp_buffer fills  with  no  pattern  having

       When the expect function returns, exp_buffer points to the
       buffer of characters that was being considered for  match-
       ing.  exp_buffer_end points to one past the last character
       in exp_buffer.  If a match occurred, exp_match points into
       exp_buffer where the match began.  exp_match_end points to
       one character past where the match ended.

       Each time new input arrives, it is compared to  each  pat-
       tern in the order they are listed.  Thus, you may test for
       absence of a match by making the  last  pattern  something
       guaranteed  to  appear,  such  as a prompt.  In situations
       where there is no prompt, you must check  for  EXP_TIMEOUT
       (just  like  you  would if you were interacting manually).
       More philosophy and strategies on specifying  expect  pat-
       terns can be found in the documentation on the expect pro-
       gram itself.  See SEE ALSO below.

       Patterns are the usual C-shell-style regular  expressions.
       For example, the following fragment looks for a successful
       login, such as from a telnet dialogue.

            switch (exp_expectl(
                 exp_glob,"invalid password",ABORT,
                 exp_end)) {
            case CONN:     /* logged in successfully */
            case BUSY:     /* couldn't log in at the moment */
            case EXP_TIMEOUT:
            case ABORT:    /* can't log in at any moment! */
            default: /* problem with expect */

       Asterisks (as in the example above) are a useful shorthand
       for omitting line-termination characters and other detail.
       Patterns must match the entire output of the current  pro-
       cess  (since  the  previous  read  on  the  descriptor  or
       stream).  More than 2000 bytes of output can force earlier
       bytes  to  be "forgotten".  This may be changed by setting
       the variable exp_match_max.  Note that  excessively  large
       values can slow down the pattern matcher.

       extern int exp_disconnected;
       int exp_disconnect();

       It is possible to move a process into the background after
       it has begun running.  A typical use for this is  to  read
       passwords  and then go into the background to sleep before
       using the passwords to do real work.

       To move a process into the background, fork, call exp_dis-
       connect()  in  the  child process and exit() in the parent
       process.  This disassociates your process  from  the  con-
       trolling terminal.  If you wish to move a process into the
       background in a different way, you must set  the  variable
       exp_disconnected  to  1.   This  allows  processes spawned
       after this point to be started correctly.

       By default, the expect functions block inside of a read on
       a single file descriptor.  If you want to wait on patterns
       from multiple file descriptors, use select,  poll,  or  an
       event manager.  They will tell you what file descriptor is
       ready to read.

       When a file descriptor is ready to read, you can  use  the
       expect  functions to do one and only read by setting time-
       out to 0.

       int fd;
       int enable;

       Pty trapping is normally done automatically by the  expect
       functions.   However,  if  you want to issue an ioctl, for
       example, directly on the slave device, you  should  tempo-
       rary disable trapping.

       Pty  trapping  can  be  controlled with exp_slave_control.
       The first argument is the file descriptor corresponding to
       the  spawned process.  The second argument is a 0 if trap-
       ping is to be disabled and 1 if it is to be enabled.

       All functions indicate errors by returning -1 and  setting

       Errors  that  occur  after the spawn functions fork (e.g.,
       attempting to spawn a non-existent program) are written to
       the  process's  stderr,  and  will  be  read  by the first

       extern int exp_reading;
       extern jmp_buf exp_readenv;

       expect uses alarm()  to  timeout,  thus  if  you  generate
       alarms during expect, it will timeout prematurely.

       Internally,  expect  calls read() which can be interrupted
       by signals.  If you define signal handlers, you can choose
       to restart or abort expect's internal read.  The variable,
       exp_reading, is true if (and only if)  expect's  read  has
       been   interrupted.   longjmp(exp_readenv,EXP_ABORT)  will
       abort  the  read.   longjmp(exp_readenv,EXP_RESTART)  will
       restart the read.

       extern int exp_loguser;
       extern int exp_logfile_all
       extern FILE *exp_logfile;

       If  exp_loguser  is  nonzero, expect sends any output from
       the spawned process to stdout.  Since interactive programs
       typically  echo their input, this usually suffices to show
       both sides of the conversation.  If  exp_logfile  is  also
       nonzero, this same output is written to the stream defined
       by exp_logfile.  If exp_logfile_all is non-zero,  exp_log-
       file is written regardless of the value of exp_loguser.

       While  I  consider  the library to be easy to use, I think
       that the standalone expect program is much,  much,  easier
       to  use  than  working  with  the C compiler and its usual
       edit, compile, debug cycle.  Unlike  typical  C  programs,
       most  of  the  debugging  isn't  getting the C compiler to
       accept your programs - rather, it is getting the  dialogue
       correct.   Also,  translating  scripts from expect to C is
       usually not necessary.  For example, the speed of interac-
       tive dialogues is virtually never an issue.  So please try
       the standalone 'expect' program first.  I suspect it is  a
       more   appropriate  solution  for  most  people  than  the

       Nonetheless, if you feel compelled to debug in C, here are
       some tools to help you.

       extern int exp_is_debugging;
       extern FILE *exp_debugfile;

       While expect dialogues seem very intuitive, trying to cod-
       ify them in a program can reveal many surprises in a  pro-
       gram's  interface.   Therefore a variety of debugging aids
       are available.  They are controlled  by  the  above  vari-
       ables, all 0 by default.

       Debugging information internal to expect is sent to stderr
       when exp_is_debugging is non-zero.  The debugging informa-
       tion  includes every character received, and every attempt
       made to match the current input against the patterns.   In
       addition,  non-printable  characters  are  translated to a
       printable form.  For example, a  control-C  appears  as  a
       caret  followed  by a C.  If exp_logfile is non-zero, this
       information is also written to that stream.

       If exp_debugfile is non-zero,  all  normal  and  debugging
       information  is  written to that stream, regardless of the
       value of exp_is_debugging.

       The stream versions  of  the  expect  functions  are  much
       slower  than the file descriptor versions because there is
       no way to portably read an unknown number of bytes without
       the  potential  of  timing out.  Thus, characters are read
       one at a time.  You are therefore strongly  encouraged  to
       use  the  file  descriptor  versions  of expect (although,
       automated versions of interactive programs  don't  usually
       demand high speed anyway).

       You can actually get the best of both worlds, writing with
       the usual stream  functions  and  reading  with  the  file
       descriptor versions of expect as long as you don't attempt
       to intermix other stream input  functions  (e.g.,  fgetc).
       To  do  this,  pass  fileno(stream) as the file descriptor
       each time.  Fortunately, there is  little  reason  to  use
       anything but the expect functions when reading from inter-
       active programs.

       There is no matching exp_pclose to exp_popen (unlike popen
       and  pclose).  It only takes two functions to close down a
       connection (fclose() followed by waiting on the pid),  but
       it  is not uncommon to separate these two actions by large
       time intervals, so the function seems of little value.

       If you are running on a Cray running Unicos  (all  I  know
       for sure from experience), you must run your compiled pro-
       gram as root or setuid.  The problem is that the Cray only
       allows root processes to open ptys.  You should observe as
       much precautions as possible:  If you don't  need  permis-
       sions,  setuid(0)  only  immediately before calling one of
       the spawn functions and immediately  set  it  back  after-

       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.)  Run-
       ning 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.

       The  exp_fexpect functions don't work at all under HP-UX -
       it appears to be a bug in getc.  Follow the advice (above)
       about  using  the exp_expect functions (which doesn't need
       to call getc).  If you fix the  problem  (before  I  do  -
       please check the latest release) let me know.

       An  alternative  to  this  library  is the expect program.
       expect interprets scripts written in a high-level language
       which direct the dialogue.  In addition, the user can take
       control and interact directly when desired.  If it is  not
       absolutely  necessary  to  write your own C program, it is
       much easier to use expect to perform the  entire  interac-
       tion.   It  is  described  further in the following refer-

       "expect: Curing Those Uncontrollable Fits  of  Interactiv-
       ity"  by  Don Libes, Proceedings of the Summer 1990 USENIX
       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.

       expect(1),   alarm(3),   read(2),   write(2),   fdopen(3),
       execve(2), execvp(3), longjmp(3), pty(4).

       There are several examples C programs in the  test  direc-
       tory  of expect's source distribution which use the expect

       Don Libes,, National Institute of Standards
       and Technology

       Thanks  to  John Ousterhout (UCBerkeley) for supplying the
       pattern matcher.

       Design and implementation of the expect library  was  paid
       for  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

                         12 December 1991                       1