FAQ 8.28 How can I call backticks without shell processing?


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This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
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8.28: How can I call backticks without shell processing?

This is a bit tricky. You can't simply write the command like this:

@ok = `grep @opts '$search_string' @filenames`;

As of Perl 5.8.0, you can use "open()" with multiple arguments. Just
like the list forms of "system()" and "exec()", no shell escapes happen.

open( GREP, "-|", 'grep', @opts, $search_string, @filenames );
chomp(@ok = <GREP>);
close GREP;

You can also:

my @ok = ();
if (open(GREP, "-|")) {
while (<GREP>) {
push(@ok, $_);
close GREP;
} else {
exec 'grep', @opts, $search_string, @filenames;

Just as with "system()", no shell escapes happen when you "exec()" a
list. Further examples of this can be found in "Safe Pipe Opens" in

Note that if you're using Windows, no solution to this vexing issue is
even possible. Even if Perl were to emulate "fork()", you'd still be
stuck, because Windows does not have an argc/argv-style API.


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