Provided by: tcl-expect-dev_5.45-7_amd64 
NAME
libexpect - programmed dialogue library with interactive programs
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
Expect_Init(interp);
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
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)