How can I run an external command and capture its output in Perl?

perl stdout stderr
gameover picture gameover · Mar 17, 2010 · Viewed 46.5k times · Source

I'm new to Perl and want to know of a way to run an external command (call it prg) in the following scenarios:

  1. Run prg, get its stdout only.
  2. Run prg, get its stderr only.
  3. Run prg, get its stdout and stderr, separately.

Answer

codaddict picture codaddict · Mar 17, 2010

You can use the backtics to execute your external program and capture its stdout and stderr.

By default the backticks discard the stderr and return only the stdout of the external program.So

$output = `cmd`;

Will capture the stdout of the program cmd and discard stderr.

To capture only stderr you can use the shell's file descriptors as:

$output = `cmd 2>&1 1>/dev/null`;

To capture both stdout and stderr you can do:

$output = `cmd 2>&1`;

Using the above you'll not be able to differenciate stderr from stdout. To separte stdout from stderr can redirect both to a separate file and read the files:

`cmd 1>stdout.txt 2>stderr.txt`;

Related questions

Can I send STDOUT and STDERR to a log file and also to the screen in Win32 Perl?

I've searched the Internet and have found some good solutions for teeing STDOUT to 2 different places. Like to a log file and also to the screen at the same time. Here's one example: use IO::Tee; my $log_filename = "log.…

Read More
How can I reinitialize Perl's STDIN/STDOUT/STDERR?

I have a Perl script which forks and daemonizes itself. It's run by cron, so in order to not leave a zombie around, I shut down STDIN,STDOUT, and STDERR: open STDIN, '/dev/null' or die "Can't read /dev/…

Read More
How to redirect STDOUT and STDERR to a variable

I want to redirect STDERR and STDOUT to a variable. I did this. close(STDOUT); close(STDERR); my $out; open(STDOUT, ">>", \$out); open(STDERR, ">>", \$out); for(1..10) { print "print\n"; # this is ok. warn "warn\n"; # same …

Read More