Perl Programming Documentation
Download Perl
Explore

Manual

- Overview
- Tutorials
- FAQs
- History / Changes
- License

Reference

- Language
- Functions
- Operators
- Special Variables
- Pragmas
- Utilities
- Internals
- Platform Specific

Modules

- A • B • C • D • E
- F • G • H • I • L
- M • N • O • P • S
- T • U • X

Tools

- Preferences

# exec

Perl 5 version 18.2 documentation
Go to top
Show recent pages
Recently read

# exec

Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage

- exec LIST

- exec PROGRAM LIST

  The `exec` function executes a system command and never returns; use `system` instead of `exec` if you want it to return. It fails and returns false only if the command does not exist and it is executed directly instead of via your system's command shell (see below).

  Since it's a common mistake to use `exec` instead of `system`, Perl warns you if `exec` is called in void context and if there is a following statement that isn't `die`, `warn`, or `exit` (if `-w` is set--but you always do that, right?). If you really want to follow an `exec` with some other statement, you can use one of these styles to avoid the warning:

          exec ('foo')   or print STDERR "couldn't exec foo: $!";    { exec ('foo') }; print STDERR "couldn't exec foo: $!";

  If there is more than one argument in LIST, or if LIST is an array with more than one value, calls execvp(3) with the arguments in LIST. If there is only one scalar argument or an array with one element in it, the argument is checked for shell metacharacters, and if there are any, the entire argument is passed to the system's command shell for parsing (this is `/bin/sh -c` on Unix platforms, but varies on other platforms). If there are no shell metacharacters in the argument, it is split into words and passed directly to `execvp` , which is more efficient. Examples:

          exec '/bin/echo', 'Your arguments are: ', @ARGV;    exec "sort $outfile | uniq";

  If you don't really want to execute the first argument, but want to lie to the program you are executing about its own name, you can specify the program you actually want to run as an "indirect object" (without a comma) in front of the LIST. (This always forces interpretation of the LIST as a multivalued list, even if there is only a single scalar in the list.) Example:

          $shell = '/bin/csh';    exec $shell '-sh';    # pretend it's a login shell

  or, more directly,

          exec {'/bin/csh'} '-sh';  # pretend it's a login shell

  When the arguments get executed via the system shell, results are subject to its quirks and capabilities. See `STRING` in perlop for details.

  Using an indirect object with `exec` or `system` is also more secure. This usage (which also works fine with system()) forces interpretation of the arguments as a multivalued list, even if the list had just one argument. That way you're safe from the shell expanding wildcards or splitting up words with whitespace in them.

          @args = ( "echo surprise" );    exec @args;               # subject to shell escapes                                # if @args == 1    exec { $args[0] } @args;  # safe even with one-arg list

  The first version, the one without the indirect object, ran the echo program, passing it `"surprise"` an argument. The second version didn't; it tried to run a program named "echo surprise", didn't find it, and set `$?` to a non-zero value indicating failure.

  Perl attempts to flush all files opened for output before the exec, but this may not be supported on some platforms (see perlport). To be safe, you may need to set `$|` ($AUTOFLUSH in English) or call the `autoflush()` method of `IO::Handle` on any open handles to avoid lost output.

  Note that `exec` will not call your `END` blocks, nor will it invoke `DESTROY` methods on your objects.

  Portability issues: exec in perlport.