bash command in Perl script - pass output <( to command

Question

If I execute following command in bash (debian 10):

comm -1 -3  <(sort $file1) <(sort $file2) > $output_file

I got the expected result.

But if I try that inside a perl script:

`comm -1 -3  <(sort $file1) <(sort $file2) > $output_file`;

I got following:

sh: 1: Syntax error: "(" unexpected

How could I make it work in perl?

Just a guess, but is there a chance Perl's using a different shell? You may find this answer How can I call a shell command in my Perl script? helpful. — radical7
– radical7, Commented Aug 2, 2022 at 19:17
@radical7 It uses /bin/sh or cmd. Some people expect $ENV{SHELL} to be used, but that makes no sense. Program-provided commands must necessarily target a specific shell, so it makes no sense to use the user's preferred shell. The env var should only be used when creating an interactive shell for the user. — ikegami
– ikegami, Commented Aug 2, 2022 at 19:33
@radical7 You were 100% correct. I was confirming with details. — ikegami
– ikegami, Commented Aug 2, 2022 at 22:12

ikegami · Accepted Answer · 2022-08-02 22:01:05Z

1

Backticks use /bin/sh (or cmd), not bash, so you'll need to construct a POSIX shell command. That command could, of course, invoke bash.

The following achieves that, while also fixing code injection bugs:

use String::ShellQuote qw( shell_quote );

my $sort_cmd1 = shell_quote( "sort", "--", $file1 ) . ' 2>&1';
my $sort_cmd2 = shell_quote( "sort", "--", $file2 ) . ' 2>&1';
my $bash_cmd  = shell_quote( "comm", "-1", "-3" ) . " <( $sort_cmd1 ) <( $sort_cmd2 )";
my $sh_cmd    = shell_quote( "bash", "-c", $bash_cmd );

my $output = `$sh_cmd`;

or

use String::ShellQuote qw( shell_quote );

my $bash_cmd = 'comm -1 -3 <( sort -- "$1" 2>&1 ) <( sort -- "$2" 2>&1 )';
my $sh_cmd = shell_quote( "bash", "-c", $bash_cmd, "dummy", $file1, $file2 );

my $output = `$sh_cmd`;

edited Aug 2, 2022 at 22:01

answered Aug 2, 2022 at 19:23

ikegami

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