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       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  commands  on  the
       program command-line (using "-c" for example).  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 debug‐
       ger has been armed.

       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_interpreter interactively prompts the user for com‐
       mands and evaluates them.  exp_interpret_cmdfile reads the given stream
       and evaluates any commands found.  exp_interpret_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  containing	 the  argument
       reproduced   with   newlines   replaced	 by  carriage-return  linefeed
       sequences.  The primary purpose of this is to allow messages to be pro‐
       duced  without  worrying	 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 executed.  The arg pointers are null-terminated
       strings.	 Following the style of execve(), arg0 (or argv[0]) is custom‐
       arily 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 num‐
       ber  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, stdout and stderr.  A	stream
       may  be	associated  with the file descriptor by using fdopen().	 (This
       should almost certainly 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 pos‐
       sible, i.e., if the environment has a controlling terminal.)  This ini‐
       tialization 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 generally comparable to	 "stty

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

       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 con‐
       trol,  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 func‐
       tion  will  be  called  after the fork and before the exec.  (This also
       modifies the behavior 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

       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 process.  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  mas‐
       ter  pty	 file descriptor and exp_pty[1] to the slave pty file descrip‐
       tor.  The expect library will not do  any  pty  initializations	(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 pro‐
       vided.  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 indicates 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 pattern 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 regexp.  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 automati‐
       cally stripped.	By default, exp_remove_nulls is set to 1 and nulls are
       automatically stripped.

       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 timeout from occurring.  A value
       of 0 causes the expect function	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 matched.

       When the expect function returns, exp_buffer points to  the  buffer  of
       characters  that	 was  being  considered	 for matching.	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  pattern  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 patterns can be
       found in the documentation on the expect program itself.	 See SEE  ALSO

       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 process (since the previous read on the
       descriptor or stream).  More than 2000 bytes of output can  force  ear‐
       lier bytes to be "forgotten".  This may be changed by setting the vari‐
       able 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_disconnect() in
       the child process and exit() in the parent process.  This disassociates
       your  process  from  the	 controlling  terminal.	 If you wish to move a
       process into the background in a different way, you must set the	 vari‐
       able  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 func‐
       tions to do one and only read by setting timeout 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 temporary disable trapping.

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

       All functions indicate errors by returning -1 and setting errno.

       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 expect.

       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_read‐
       env,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_logfile is written regardless of the value of exp_loguser.

       While I consider the library to be easy to use, I think that the stand‐
       alone 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  interactive  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 library.

       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 codify them in a
       program can reveal many surprises in a program's interface.   Therefore
       a  variety of debugging aids are available.  They are controlled by the
       above variables, all 0 by default.

       Debugging information  internal	to  expect  is	sent  to  stderr  when
       exp_is_debugging is non-zero.  The debugging information includes every
       character received, and every attempt made to match the	current	 input
       against the patterns.  In addition, non-printable characters are trans‐
       lated 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  encour‐
       aged to use the file descriptor versions of expect (although, automated
       versions of interactive programs don't usually demand high  speed  any‐

       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 any‐
       thing but the expect functions when reading from interactive 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() fol‐
       lowed 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

       If you are running on a Cray running Unicos (all I know for  sure  from
       experience), you must run your compiled program 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 per‐
       missions, setuid(0) only immediately before calling one	of  the	 spawn
       functions and immediately set it back afterwards.

       Normally, spawn takes little time to execute.  If you notice spawn tak‐
       ing 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	inter‐
       prets  scripts  written	in a high-level language which direct the dia‐
       logue.  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 references:

       "expect:	 Curing	 Those	Uncontrollable	Fits  of Interactivity" by Don
       Libes, Proceedings of the Summer 1990 USENIX Conference, Anaheim, Cali‐
       fornia, June 11-15, 1990.

       "Using  expect  to  Automate System Administration Tasks" by Don Libes,
       Proceedings of the 1990 USENIX Large Installation  Systems  Administra‐
       tion 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 directory of expect's
       source distribution which use the expect library.

       Don Libes,, National Institute of Standards and Technol‐

       Thanks to  John	Ousterhout  (UCBerkeley)  for  supplying  the  pattern

       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 used.

			       12 December 1991			  LIBEXPECT(3)

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