1IPC::Cmd(3pm) Perl Programmers Reference Guide IPC::Cmd(3pm)
2
6 IPC::Cmd - finding and running system commands made easy
7
9 use IPC::Cmd qw[can_run run run_forked];
10 my $full_path = can_run('wget') or warn 'wget is not installed!';
12 ### commands can be arrayrefs or strings ###
14 my $cmd = "$full_path -b theregister.co.uk";
15 my $cmd = [$full_path, '-b', 'theregister.co.uk'];
16 ### in scalar context ###
18 my $buffer;
19 if( scalar run( command => $cmd,
20 verbose => 0,
21 buffer => \$buffer,
22 timeout => 20 )
23 ) {
24 print "fetched webpage successfully: $buffer\n";
25 }
26 ### in list context ###
29 my( $success, $error_code, $full_buf, $stdout_buf, $stderr_buf ) =
30 run( command => $cmd, verbose => 0 );
31 if( $success ) {
33 print "this is what the command printed:\n";
34 print join "", @$full_buf;
35 }
36 ### check for features
38 print "IPC::Open3 available: " . IPC::Cmd->can_use_ipc_open3;
39 print "IPC::Run available: " . IPC::Cmd->can_use_ipc_run;
40 print "Can capture buffer: " . IPC::Cmd->can_capture_buffer;
41 ### don't have IPC::Cmd be verbose, ie don't print to stdout or
43 ### stderr when running commands -- default is '0'
44 $IPC::Cmd::VERBOSE = 0;
45
47 IPC::Cmd allows you to run commands, interactively if desired, platform
48 independent but have them still work.
49 The "can_run" function can tell you if a certain binary is installed
51 and if so where, whereas the "run" function can actually execute any of
52 the commands you give it and give you a clear return value, as well as
53 adhere to your verbosity settings.
54
56 $ipc_run_version = IPC::Cmd->can_use_ipc_run( [VERBOSE] )
57 Utility function that tells you if "IPC::Run" is available. If the
58 verbose flag is passed, it will print diagnostic messages if "IPC::Run"
59 can not be found or loaded.
60 $ipc_open3_version = IPC::Cmd->can_use_ipc_open3( [VERBOSE] )
62 Utility function that tells you if "IPC::Open3" is available. If the
63 verbose flag is passed, it will print diagnostic messages if
64 "IPC::Open3" can not be found or loaded.
65 $bool = IPC::Cmd->can_capture_buffer
67 Utility function that tells you if "IPC::Cmd" is capable of capturing
68 buffers in it's current configuration.
69 $bool = IPC::Cmd->can_use_run_forked
71 Utility function that tells you if "IPC::Cmd" is capable of providing
72 "run_forked" on the current platform.
73
75 $path = can_run( PROGRAM );
76 "can_run" takes but a single argument: the name of a binary you wish to
77 locate. "can_run" works much like the unix binary "which" or the bash
78 command "type", which scans through your path, looking for the
79 requested binary .
80 Unlike "which" and "type", this function is platform independent and
82 will also work on, for example, Win32.
83 It will return the full path to the binary you asked for if it was
85 found, or "undef" if it was not.
86 $ok | ($ok, $err, $full_buf, $stdout_buff, $stderr_buff) = run( command =>
88 COMMAND, [verbose => BOOL, buffer => \$SCALAR, timeout => DIGIT] );
89 "run" takes 4 arguments:
90 command
92 This is the command to execute. It may be either a string or an
93 array reference. This is a required argument.
94 See CAVEATS for remarks on how commands are parsed and their
96 limitations.
97 verbose
99 This controls whether all output of a command should also be
100 printed to STDOUT/STDERR or should only be trapped in buffers
101 (NOTE: buffers require "IPC::Run" to be installed or your system
102 able to work with "IPC::Open3").
103 It will default to the global setting of $IPC::Cmd::VERBOSE, which
105 by default is 0.
106 buffer
108 This will hold all the output of a command. It needs to be a
109 reference to a scalar. Note that this will hold both the STDOUT
110 and STDERR messages, and you have no way of telling which is which.
111 If you require this distinction, run the "run" command in list
112 context and inspect the individual buffers.
113 Of course, this requires that the underlying call supports buffers.
115 See the note on buffers right above.
116 timeout
118 Sets the maximum time the command is allowed to run before
119 aborting, using the built-in "alarm()" call. If the timeout is
120 triggered, the "errorcode" in the return value will be set to an
121 object of the "IPC::Cmd::TimeOut" class. See the "errorcode"
122 section below for details.
123 Defaults to 0, meaning no timeout is set.
125 "run" will return a simple "true" or "false" when called in scalar
127 context. In list context, you will be returned a list of the following
128 items:
129 success
131 A simple boolean indicating if the command executed without errors
132 or not.
133 error message
135 If the first element of the return value (success) was 0, then some
136 error occurred. This second element is the error message the
137 command you requested exited with, if available. This is generally
138 a pretty printed value of $? or $@. See "perldoc perlvar" for
139 details on what they can contain. If the error was a timeout, the
140 "error message" will be prefixed with the string
141 "IPC::Cmd::TimeOut", the timeout class.
142 full_buffer
144 This is an arrayreference containing all the output the command
145 generated. Note that buffers are only available if you have
146 "IPC::Run" installed, or if your system is able to work with
147 "IPC::Open3" -- See below). This element will be "undef" if this
148 is not the case.
149 out_buffer
151 This is an arrayreference containing all the output sent to STDOUT
152 the command generated. Note that buffers are only available if you
153 have "IPC::Run" installed, or if your system is able to work with
154 "IPC::Open3" -- See below). This element will be "undef" if this
155 is not the case.
156 error_buffer
158 This is an arrayreference containing all the output sent to STDERR
159 the command generated. Note that buffers are only available if you
160 have "IPC::Run" installed, or if your system is able to work with
161 "IPC::Open3" -- See below). This element will be "undef" if this
162 is not the case.
163 See the "HOW IT WORKS" Section below to see how "IPC::Cmd" decides what
165 modules or function calls to use when issuing a command.
166 $hashref = run_forked( command => COMMAND, { child_stdin => SCALAR, timeout
168 => DIGIT, stdout_handler => CODEREF, stderr_handler => CODEREF} );
169 "run_forked" is used to execute some program, optionally feed it with
170 some input, get its return code and output (both stdout and stderr into
171 seperate buffers). In addition it allows to terminate the program
172 which take too long to finish.
173 The important and distinguishing feature of run_forked is execution
175 timeout which at first seems to be quite a simple task but if you think
176 that the program which you're spawning might spawn some children itself
177 (which in their turn could do the same and so on) it turns out to be
178 not a simple issue.
179 "run_forked" is designed to survive and successfully terminate almost
181 any long running task, even a fork bomb in case your system has the
182 resources to survive during given timeout.
183 This is achieved by creating separate watchdog process which spawns the
185 specified program in a separate process session and supervises it:
186 optionally feeds it with input, stores its exit code, stdout and
187 stderr, terminates it in case it runs longer than specified.
188 Invocation requires the command to be executed and optionally a hashref
190 of options:
191 "timeout"
193 Specify in seconds how long the command may run for before it is
194 killed with with SIG_KILL (9) which effectively terminates it and
195 all of its children (direct or indirect).
196 "child_stdin"
198 Specify some text that will be passed into "STDIN" of the executed
199 program.
200 "stdout_handler"
202 You may provide a coderef of a subroutine that will be called a
203 portion of data is received on stdout from the executing program.
204 "stderr_handler"
206 You may provide a coderef of a subroutine that will be called a
207 portion of data is received on stderr from the executing program.
208 "run_forked" will return a HASHREF with the following keys:
210 "exit_code"
212 The exit code of the executed program.
213 "timeout"
215 The number of seconds the program ran for before being terminated,
216 or 0 if no timeout occurred.
217 "stdout"
219 Holds the standard output of the executed command (or empty string
220 if there were no stdout output; it's always defined!)
221 "stderr"
223 Holds the standard error of the executed command (or empty string
224 if there were no stderr output; it's always defined!)
225 "merged"
227 Holds the standard output and error of the executed command merged
228 into one stream (or empty string if there were no output at all;
229 it's always defined!)
230 "err_msg"
232 Holds some explanation in the case of an error.
233 $q = QUOTE
235 Returns the character used for quoting strings on this platform. This
236 is usually a "'" (single quote) on most systems, but some systems use
237 different quotes. For example, "Win32" uses """ (double quote).
238 You can use it as follows:
240 use IPC::Cmd qw[run QUOTE];
242 my $cmd = q[echo ] . QUOTE . q[foo bar] . QUOTE;
243 This makes sure that "foo bar" is treated as a string, rather than two
245 seperate arguments to the "echo" function.
246 __END__
248
250 "run" will try to execute your command using the following logic:
251 · If you have "IPC::Run" installed, and the variable
253 $IPC::Cmd::USE_IPC_RUN is set to true (See the "GLOBAL VARIABLES"
254 Section) use that to execute the command. You will have the full
255 output available in buffers, interactive commands are sure to work
256 and you are guaranteed to have your verbosity settings honored
257 cleanly.
258 · Otherwise, if the variable $IPC::Cmd::USE_IPC_OPEN3 is set to true
260 (See the "GLOBAL VARIABLES" Section), try to execute the command
261 using "IPC::Open3". Buffers will be available on all platforms
262 except "Win32", interactive commands will still execute cleanly,
263 and also your verbosity settings will be adhered to nicely;
264 · Otherwise, if you have the verbose argument set to true, we fall
266 back to a simple system() call. We cannot capture any buffers, but
267 interactive commands will still work.
268 · Otherwise we will try and temporarily redirect STDERR and STDOUT,
270 do a system() call with your command and then re-open STDERR and
271 STDOUT. This is the method of last resort and will still allow you
272 to execute your commands cleanly. However, no buffers will be
273 available.
274
276 The behaviour of IPC::Cmd can be altered by changing the following
277 global variables:
278 $IPC::Cmd::VERBOSE
280 This controls whether IPC::Cmd will print any output from the commands
281 to the screen or not. The default is 0;
282 $IPC::Cmd::USE_IPC_RUN
284 This variable controls whether IPC::Cmd will try to use IPC::Run when
285 available and suitable. Defaults to true if you are on "Win32".
286 $IPC::Cmd::USE_IPC_OPEN3
288 This variable controls whether IPC::Cmd will try to use IPC::Open3 when
289 available and suitable. Defaults to true.
290 $IPC::Cmd::WARN
292 This variable controls whether run time warnings should be issued, like
293 the failure to load an "IPC::*" module you explicitly requested.
294 Defaults to true. Turn this off at your own risk.
296
298 Whitespace and IPC::Open3 / system()
299 When using "IPC::Open3" or "system", if you provide a string as the
300 "command" argument, it is assumed to be appropriately escaped. You
301 can use the "QUOTE" constant to use as a portable quote character
302 (see above). However, if you provide and "Array Reference",
303 special rules apply:
304 If your command contains "Special Characters" (< > | &), it will be
306 internally stringified before executing the command, to avoid that
307 these special characters are escaped and passed as arguments
308 instead of retaining their special meaning.
309 However, if the command contained arguments that contained
311 whitespace, stringifying the command would loose the significance
312 of the whitespace. Therefor, "IPC::Cmd" will quote any arguments
313 containing whitespace in your command if the command is passed as
314 an arrayref and contains special characters.
315 Whitespace and IPC::Run
317 When using "IPC::Run", if you provide a string as the "command"
318 argument, the string will be split on whitespace to determine the
319 individual elements of your command. Although this will usually
320 just Do What You Mean, it may break if you have files or commands
321 with whitespace in them.
322 If you do not wish this to happen, you should provide an array
324 reference, where all parts of your command are already separated
325 out. Note however, if there's extra or spurious whitespace in
326 these parts, the parser or underlying code may not interpret it
327 correctly, and cause an error.
328 Example: The following code
330 gzip -cdf foo.tar.gz | tar -xf -
332 should either be passed as
334 "gzip -cdf foo.tar.gz | tar -xf -"
336 or as
338 ['gzip', '-cdf', 'foo.tar.gz', '|', 'tar', '-xf', '-']
340 But take care not to pass it as, for example
342 ['gzip -cdf foo.tar.gz', '|', 'tar -xf -']
344 Since this will lead to issues as described above.
346 IO Redirect
348 Currently it is too complicated to parse your command for IO
349 Redirections. For capturing STDOUT or STDERR there is a work around
350 however, since you can just inspect your buffers for the contents.
351 Interleaving STDOUT/STDERR
353 Neither IPC::Run nor IPC::Open3 can interleave STDOUT and STDERR.
354 For short bursts of output from a program, ie this sample:
355 for ( 1..4 ) {
357 $_ % 2 ? print STDOUT $_ : print STDERR $_;
358 }
359 IPC::[Run|Open3] will first read all of STDOUT, then all of STDERR,
361 meaning the output looks like 1 line on each, namely '13' on STDOUT
362 and '24' on STDERR.
363 It should have been 1, 2, 3, 4.
365 This has been recorded in rt.cpan.org as bug #37532: Unable to
367 interleave STDOUT and STDERR
368
370 "IPC::Run", "IPC::Open3"
371
373 Thanks to James Mastros and Martijn van der Streek for their help in
374 getting IPC::Open3 to behave nicely.
375 Thanks to Petya Kohts for the "run_forked" code.
377
379 Please report bugs or other issues to <bug-ipc-cmd@rt.cpan.org>.
380
382 This module by Jos Boumans <kane@cpan.org>.
383
385 This library is free software; you may redistribute and/or modify it
386 under the same terms as Perl itself.
387perl v5.12.4 2011-06-07 IPC::Cmd(3pm)