Redirecting STDOUT to a variable

Dave05 has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

I want to capture the output of a program that prints on STDOUT. I could redirect STDOUT to a file like this:

# See the Cookbook p.263 for redirecting standard output. 
# Copy the STDOUT file descriptors:
my $buffer_file = '/path/to/buffer.txt';
open(OLDOUT, ">&STDOUT");
open(STDOUT, "> $buffer_file") or die "Couldn't redirect STDOUT to $bu
+ffer_file: $!";

# Call the script whose output I want to capture:
do("/path/to/cgi/mhandler.cgi");

# Close the redirected STDOUT and restore the original:    
close(STDOUT) or die "Couldn't close redirected STDOUT: $!";
open(STDOUT, ">&OLDOUT") or die "Couldn't restore STDOUT: $!";
close(OLDOUT) or die "Couldn't close OLDOUT: $!";
[download]

But it would be more useful if I could capture the STDOUT directly into a $buffer variable instead of a file.

Is it possible to open a filehandle into a variable like that?

Comment on Redirecting STDOUT to a variable Download Code

Replies are listed 'Best First'.
Re: Redirecting STDOUT to a variable by davis (Vicar) on Sep 10, 2002 at 10:48 UTC
You want `qx` (Quoted execution) or the backticks operator: #!/usr/bin/perl use warnings; use strict; my $output = `nslookup www.perlmonks.org`; #or qx print "=====\n"; print $output; print "=====\n"; [download] See `perldoc perlop`, and look for `Quote and Quote-like Operators` for more information Cheers Update: Also look for `qx/STRING/` in the above manpage - it's more relevant Update 2: Search for "capture STDOUT" in the search box, and you'll find How to capture data from STDOUT?. If it's a simple question, it's almost certainly been asked (and answered) before, so please remember to search first. davis Is this going out live? No, Homer, very few cartoons are broadcast live - it's a terrible strain on the animator's wrist	[reply] [d/l]
Re: Redirecting STDOUT to a variable by jmcnamara (Monsignor) on Sep 10, 2002 at 11:10 UTC
Have a look at the IO::Scalar module which is part of the IO::Stringy distribution: `#!/usr/bin/perl -w use strict; use IO::Scalar; my $str; tie STDOUT, 'IO::Scalar', \$str; print "hello, world"; untie STDOUT; print "The data is here: ",$str;` [download] -- John.	[reply] [d/l]
Re: Redirecting STDOUT to a variable by blssu (Pilgrim) on Sep 10, 2002 at 11:26 UTC
Perl 5.8 has the ability to open strings (scalars) as files, but that feature does not work for capturing output of other programs -- use the backtick method above for that. If you want to capture the output of a subroutine or module inside your own Perl code, the string file technique works well. I'm including it here because this node is likely to turn up in a search. `use strict; use PerlIO::scalar; my $output; my $file; if (open($file, ">", \$output)) { print $file "This is a test.\n"; close($file); print $output; }` [download] If you want to redirect STDOUT to a scalar, close it first and then open it connected to the string scalar. You will get an error if you try to do anything that requires a "real" file. (Calling `system(...)` will fail for example.)	[reply] [d/l] [select]
Re: Redirecting STDOUT to a variable by ash (Monk) on Sep 10, 2002 at 13:52 UTC
You'd just use a TIEHANDLE. See perldoc tie and perldoc Tie::Handle. -- ash/asksh <ask@unixmonks.net>	[reply]
Re: Redirecting STDOUT to a variable by antichef (Acolyte) on Sep 12, 2002 at 17:16 UTC
You can open a handle similar to a file handle like: `open (STDOUTHANDLE, "somecommand\|"); while ($line = <STDOUTHANDLE>) { # . . . }` [download] note the pipe character at the end of the command.	[reply] [d/l]