How do I get both the return value and text? backticks vs. system()

[flymolo]

`some command` will give me the text of the executed program. system("command") will return the return value, but running the program twice might change text and/or return values. Is there any easy way to do this? Right now I'm thinking system("command >file") but then I'd have a file I don't need.

Originally posted as a Categorized Question.

[chromatic]

Use backticks to get output from an executed program. Check $? for the error returned.

A pipe would work in this case, but backticks are probably simpler.

Originally posted as a Categorized Answer.

[david2008]

Update: I got confused between $? and $!. Sorry
Hi

I suspect that we can not rely on $? alone.
From this perlmonks post
$! having a non-false value is not an indication anything is wrong.

BR,
David

[lhoward]

open has a piping syntax that you can use to pipe data to or from a program. You can get the exit value from $? (see perlvar).

open P,"command |" or die "error running command $!";
my @data=<p>;
close P;
my $exit_value=$? >> 8;

[Archon810]

Having used the new Perl 5.10, I was shocked to find this new variable after months of use:

${^CHILD_ERROR_NATIVE}

This variable gives the native status returned by the last pipe close, backtick command, successful call to wait() or waitpid(), or from the system() operator. See perlrun for details. (Contributed by Gisle Aas.)

New internal variables

Finally!.. what else can I say?

[jffry]

If you especially don't want the shell interpreting shell metacharacters, then don't pass the command to the shell, use the 4+ argument form of open.

open(CMD, '-|', '/usr/bin/ls', '$4', '$PATH');
my $output = do { local $/; <CMD> };
close CMD;
print "$output\n";

Here is the output, you'll see that the "$4" and "$PATH" were not interpreted as variables before being sent to ls.

ls: 0653-341 The file $4 does not exist.
ls: 0653-341 The file $PATH does not exist.