Introduction to Library Functions LIBEXPECT(3)
NAME
libexpect - programmed dialogue library with interactive
programsDESCRIPTION
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 alreadyexist, however aliases beginning with "exp_" are always
created for expect commands. So for example, "send" can beused as "exp_send".
Generally, you should only call Expect commands viaTcl_Eval. Certain auxiliary functions may be called
directly. They are summarized below. They may be useful inconstructing 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. Aprototype 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 example).
SunOS 5.10 Last change: 12 December 1991 1 Introduction to Library Functions LIBEXPECT(3)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 com-
mands. 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 listedhere are initialized appropriately. exp_interpreter
interactively prompts the user for commands and evaluatesthem. 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 func-
tion that to interp->result.
SYNOPSIS
#include
intexp_spawnl(file, arg0 [, arg1, ..., argn] (char *)0);
char *file; char *arg0, *arg1, ... *argn; intexp_spawnv(file,argv);
char *file, *argv[ ]; intexp_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)();
SunOS 5.10 Last change: 12 December 1991 2 Introduction to Library Functions LIBEXPECT(3)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 dupli-
cate 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 compiletime. 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 certainlybe 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); } SunOS 5.10 Last change: 12 December 1991 3 Introduction to Library Functions LIBEXPECT(3)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 pro-
cess. 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 skippedby setting exp_ttycopy to 0.
The pty is further initialized to some system wide defaultsif exp_ttyinit is non-zero. The default is generally com-
parable to "stty sane".The tty setting can be further modified by setting the vari-
able 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 variableexp_console to 1.
Between the time a process is started and the new program isgiven control, the spawn functions can clean up the environ-
ment by closing file descriptors. By default, the only file descriptors closed are ones internal to Expect and anymarked "close-on-exec".
If needed, you can close additional file descriptors by creating an appropriate function and assigning it toexp_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 thefunction 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 rede-
fine this for effects such as manipulating the uid or the signals. IF YOU WANT TO ALLOCATE YOUR OWN PTYextern int exp_autoallocpty;
extern int exp_pty[2];
SunOS 5.10 Last change: 12 December 1991 4 Introduction to Library Functions LIBEXPECT(3)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, setexp_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 isspawned. After the process is started, all further communi-
cation 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 froma process spawned by exp_spawnl or exp_spawnv, more con-
venient functions are provided. They are as follows: intexp_expectl(fd,type1,pattern1,[re1,],value1,type2,...,exp_end);
int fd;enum exp_type type;
char *pattern1, *pattern2, ...; regexp *re1, *re2, ...; int value1, value2, ...; intexp_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; }; SunOS 5.10 Last change: 12 December 1991 5 Introduction to Library Functions LIBEXPECT(3) intexp_expectv(fd,cases);
int fd;struct exp_case *cases;
intexp_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 functionsexp_expectl and exp_fexpectl, any pattern compilation done
internally is thrown away after the function returns. Thefunctions 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, thematched string can be found in re->startp[0]. The match
substrings (according to the parentheses) in the originalpattern can be found in re->startp[1], re->startp[2], and so
SunOS 5.10 Last change: 12 December 1991 6 Introduction to Library Functions LIBEXPECT(3)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 denotedby a struct exp_case with type exp_end. For the rest of
this discussion, these functions will be referred to generi-
cally as expect. If a pattern matches, then the corresponding integer value is returned. Values need not be unique, however they shouldbe 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 settingthe 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 wherethere is no prompt, you must check for EXP_TIMEOUT (just
like you would if you were interacting manually). More phi-
losophy 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 SunOS 5.10 Last change: 12 December 1991 7 Introduction to Library Functions LIBEXPECT(3) 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 shorthandfor 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 variableexp_match_max. Note that excessively large values can slow
down the pattern matcher. RUNNING IN THE BACKGROUNDextern 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, callexp_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 variableexp_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 SunOS 5.10 Last change: 12 December 1991 8 Introduction to Library Functions LIBEXPECT(3) expect functions to do one and only read by setting timeout to 0. SLAVE CONTROL voidexp_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. SIGNALSextern 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. LOGGINGextern 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 typi-
cally echo their input, this usually suffices to show both SunOS 5.10 Last change: 12 December 1991 9 Introduction to Library Functions LIBEXPECT(3)sides of the conversation. If exp_logfile is also nonzero,
this same output is written to the stream defined byexp_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 usethan working with the C compiler and its usual edit, com-
pile, debug cycle. Unlike typical C programs, most of thedebugging isn't getting the C compiler to accept your pro-
grams - rather, it is getting the dialogue correct. Also,
translating scripts from expect to C is usually not neces-
sary. 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'sinterface. Therefore a variety of debugging aids are avail-
able. They are controlled by the above variables, all 0 by default. Debugging information internal to expect is sent to stderrwhen 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. Inaddition, 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 informa-
tion is also written to that stream.If exp_debugfile is non-zero, all normal and debugging
information is written to that stream, regardless of thevalue 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 toportably read an unknown number of bytes without the poten-
tial 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 SunOS 5.10 Last change: 12 December 1991 10 Introduction to Library Functions LIBEXPECT(3) 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 anythingbut the expect functions when reading from interactive pro-
grams.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 allowsroot processes to open ptys. You should observe as much pre-
cautions 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 withthe -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: SunOS 5.10 Last change: 12 December 1991 11 Introduction to Library Functions LIBEXPECT(3) "expect: Curing Those Uncontrollable Fits of Interactivity"by Don Libes, Proceedings of the Summer 1990 USENIX Confer-
ence, 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.ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
|____________________|__________________|_
| Availability | shell/expect ||____________________|__________________|_
| Interface Stability| Uncommitted ||____________________|_________________|
NOTES Source for expect is available on http://opensolaris.org. SunOS 5.10 Last change: 12 December 1991 12