libexpect

LIBEXPECT(3)               Library Functions Manual               LIBEXPECT(3)



NAME
       libexpect - programmed dialogue with interactive programs - C functions

DESCRIPTION
       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.

SYNOPSIS
       #include expect_tcl.h
       Exp_Init(interp);

       cc files... -lexpect -ltcl -lm

       The Exp_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
       debugger 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
       commands 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 produced 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.

SYNOPSIS
       #include <expect.h>

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

       int
       exp_spawnv(file,argv);
       char *file, *argv[ ];

       int
       exp_spawnfd(fd);
       int fd;

       FILE *
       exp_popen(command);
       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


DESCRIPTION
       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
       customarily 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, 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 *
       exp_popen(program)
       char *program;
       {
            FILE *fp;
            int ec;

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

       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 generally 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 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
       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.


IF YOU WANT TO ALLOCATE YOUR OWN PTY
       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
       master pty file descriptor and exp_pty[1] to the slave pty file
       descriptor.  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 descriptor.

       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.

EXPECT PROCESSING
       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
       exp_expectl(fd,type1,pattern1,[re1,],value1,type2,...,exp_end);
       int fd;
       enum exp_type type;
       char *pattern1, *pattern2, ...;
       regexp *re1, *re2, ...;
       int value1, value2, ...;

       int
       exp_fexpectl(fp,type1,pattern1,[re1,]value1,type2,...,exp_end);
       FILE *fp;
       enum exp_type type;
       char *pattern1, *pattern2, ...;
       regexp *re1, *re2, ...;
       int value1, value2, ...;

       enum exp_type {
       exp_end,
       exp_glob,
       exp_exact,
       exp_regexp,
       exp_compiled,
       exp_null,
       };

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

       int
       exp_expectv(fd,cases);
       int fd;
       struct exp_case *cases;

       int
       exp_fexpectv(fp,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
       automatically 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
       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,"connected",CONN,
                 exp_glob,"busy",BUSY,
                 exp_glob,"failed",ABORT,
                 exp_glob,"invalid password",ABORT,
                 exp_end)) {
            case CONN:     /* logged in successfully */
                 break;
            case BUSY:     /* couldn't log in at the moment */
                 break;
            case EXP_TIMEOUT:
            case ABORT:    /* can't log in at any moment! */
                 break;
            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
       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.

RUNNING IN THE BACKGROUND
       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
       variable exp_disconnected to 1.  This allows processes spawned after
       this point to be started correctly.

MULTIPLEXING
       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 timeout to 0.

SLAVE CONTROL
       void
       exp_slave_control(fd,enable)
       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
       argument 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.


ERRORS
       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.

SIGNALS
       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.

LOGGING
       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.


DEBUGGING
       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 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
       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.

CAVEATS
       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 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()
       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 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
       permissions, 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
       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.

BUGS
       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.

SEE ALSO
       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
       interaction.  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,
       California, June 11-15, 1990.

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

AUTHOR
       Don Libes, libes@nist.gov, National Institute of Standards and
       Technology

ACKNOWLEDGEMENTS
       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 used.



                               12 December 1991                   LIBEXPECT(3)