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system() and qx comparison

by didess (Sexton)
on Sep 27, 2011 at 21:55 UTC ( #928192=perlquestion: print w/ replies, xml ) Need Help??
didess has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks! I know there are two forms for submitting a command to system :

One through the shell with the command and its parameters in one single scalar system('echo $LANG'); for example.

One without the shell, with the command and its parameters in a list. like system('echo','$LANG');

With this second form, the command echo will print '$LANG' without any resolution of the variable LANG.

Can I get these two different ways , and how if yes, with the qx syntax : qx {echo $LANG} ?

Thanks to you!

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Re: system() and qx comparison
by ikegami (Pope) on Sep 27, 2011 at 23:25 UTC

    IPC::System::Simple provides capture and capturex which are single- and multi-arg versions of qw respectively.

    use IPC::System::Simple qw( capture capturex ); my $foo = capture("shell command"); my $foo = capturex("program"); my $foo = capturex("program", @args);

    Conveniently, they even do the error checking for you.

    By the way, IPC::System::Simple can also add error checking to system.

    use IPC::System::Simple qw( system systemx ); system("shell command"); systemx("program"); systemx("program", @args);
      Thank you a lot. It really seems to be what I was looking for !!!!
Re: system() and qx comparison
by Kc12349 (Monk) on Sep 27, 2011 at 22:00 UTC

    Remove the single quotes from around $LANG in your second form or replace them with double quotes.

    qx is another form for backticks, which in perl will capture the return from the system call.

    my $return = qx{echo $LANG}; say $return;
      thanks for your answer;

      but, if replace single quotes by doubles quotes with qx, $LANG will be resolved as a Perl variable, not as a shell environment variable

      This little code will show it clearly:
      cat #!/usr/bin/perl my $LANG = "script internal"; system('echo $LANG'); system('echo','$LANG'); my @out = qx "echo $LANG"; chomp(@out); print "out=@out\n"; my @out = qx' echo $LANG '; chomp(@out); print "out=@out\n";

      it's output is :

      ./ fr_FR.UTF-8 $LANG out=script internal out=fr_FR.UTF-8

      In fact i'd like to pass parameters to the command (the "echo" program in this little example), with possibly $, *, and such characters which the shell interpretes. while avoiding a large collection of antislashes. May be, it's not possible with qx and I must use system(). That's what I'd like to know</p

        If you want the environments LANG variable, use $ENV{LANG}.

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