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capturing the output of eval()

by tmbg (Novice)
on May 09, 2001 at 20:00 UTC ( #79135=perlquestion: print w/replies, xml ) Need Help??
tmbg has asked for the wisdom of the Perl Monks concerning the following question:

I've got a bit of code stored in $_, and I want to be able to eval the code and capture what would be printed to STDOUT and STDERR.

Currently I can only get the return value, which of a print statement is 1

Replies are listed 'Best First'.
Re (tilly) 1: capturing the output of eval()
by tilly (Archbishop) on May 09, 2001 at 20:20 UTC
    Two options.

    You can fork, eval in the child, and capture the output in the parent.

    You can use open to dup the original STDOUT and STDERR somewhere else, tie STDOUT and STDERR (eg with IO::Scalar), eval, untie and replace with the originals.

Re: capturing the output of eval()
by mr.nick (Chaplain) on May 09, 2001 at 20:46 UTC
Re: capturing the output of eval()
by damian1301 (Curate) on May 09, 2001 at 20:21 UTC
    To get the output of STDERR, eval comes along with a neat variable that captures the errors during the evaluation process.

    To capture STDOUT, you have two options:
    • Log STDOUT from the beginning
    • Print it a file. Then open that file and print it to the screen. This is what I hacked up and I am *certain* there is a better way for one of these.

    Log from beginning:
    BEGIN{ open(STDOUT,">stdout.log")||die"$!"; }

    #!/usr/bin/perl use strict; open(LOG,"log.txt") ||die"$!"; select LOG; stuff here close LOG; select STDOUT; # I love ar0n :) my $thing = do { local @ARGV = "foo.txt"; <> }; print $thing;
    That way you get the stuff printed to the file and to STDOUT. I am sure there is a better way to do it. Monks, enlighten me(us). :)
    UPDATE: I just noticed I really messed up on the question. Forgive me.

    Tiptoeing up to a Perl hacker.
    Dave AKA damian

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