How to pipe the content of a variable as STDIN in a qx{} statement in Perl?

Question

I basically would like to do this:

$_ = \"some content that need to be escaped &>|\\\"$\\\'`\\s\\\\\";
qx{echo $_ | foo}

There are

Answer 1

The following assume @cmd contains the program and its arguments (if any).

my @cmd = ('foo');

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If you want to capture the output, you can use any of the following:

use String::ShellQuote qw( shell_quote );
my $cmd1 = shell_quote('printf', '%s', $_);
my $cmd2 = shell_quote(@cmd);
my $output = qx{$cmd1 | $cmd2};

use IPC::Run3 qw( run3 );
run3(\@cmd, \$_, \my $output);

use IPC::Run qw( run );
run(\@cmd, \$_, \my $output);

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If you don't want to capture the output, you can use any of the following:

use String::ShellQuote qw( shell_quote );
my $cmd1 = shell_quote('printf', '%s', $_);
my $cmd2 = shell_quote(@cmd);
system("$cmd1 | $cmd2");

system('/bin/sh', '-c', 'printf "%s" "$0" | "$@"', $_, @cmd);

use String::ShellQuote qw( shell_quote );
my $cmd = shell_quote(@cmd);
open(my $pipe, '|-', $cmd);
print($pipe $_);
close($pipe);

open(my $pipe, '|-', '/bin/sh', '-c', '"$@"', 'dummy', @cmd);
print($pipe $_);
close($pipe);

use IPC::Run3 qw( run3 );
run3(\@cmd, \$_);

use IPC::Run qw( run );
run(\@cmd, \$_);

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If you don't want to capture the output, but you don't want to see it either, you can use any of the following:

use String::ShellQuote qw( shell_quote );
my $cmd1 = shell_quote('printf', '%s', $_);
my $cmd2 = shell_quote(@cmd);
system("$cmd1 | $cmd2 >/dev/null");

system('/bin/sh', '-c', 'printf "%s" "$0" | "$@" >/dev/null', $_, @cmd);

use String::ShellQuote qw( shell_quote );
my $cmd = shell_quote(@cmd);
open(my $pipe, '|-', "$cmd >/dev/null");
print($pipe $_);
close($pipe);

open(my $pipe, '|-', '/bin/sh', '-c', '"$@" >/dev/null', 'dummy', @cmd);
print($pipe $_);
close($pipe);

use IPC::Run3 qw( run3 );
run3(\@cmd, \$_, \undef);

use IPC::Run qw( run );
run(\@cmd, \$_, \undef);

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Notes:

• The solutions using printf will impose a limit on the size of the data to pass to the program's STDIN.

• The solutions using printf are unable to pass a NUL to the program's STDIN.

• The presented solutions that use IPC::Run3 and IPC::Run don't involve a shell. This avoids problems.

• You should probably use system and capture from IPC::System::Simple instead of the builtin system and qx to get "free" error checking.