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How to connect processes via pipe in Perl?

I want to write a Perl script which runs the programs foo and bar and processes stdout of foo and emits it to stdin of bar in a streaming fashion. The Perl script should act like this bash command:

foo

bar

stdout

foo

stdin

bar

bash

$ foo | some-perl-code | bar


I managed to do the first part with the snippet below. I start the program foo and open the pipe to read stdout.

foo

stdout

open( my $pipe_fh, "foo |" );
while ( my $row = <$pipe_fh> )
# do stuff
print $row;



How can I realize the second part? How can I emit $row to the program bar within my Perl script?

$row

bar

3 Answers
3

Just use another open, but revert the direction of the pipe:

open my $in, '-|', 'foo' or die $!;
open my $out, '|-', 'bar' or die $!;
while ( my $row = <$in> )
# do stuff
print $out $row;



Another option is using IPC::Pipeline to chain the processes together instead of doing it manually.

IPC::Run is also another (somewhat daunting) option. If you end up with complex pipelines, may I also recommend (shameless promotion of own module) IPC::PrettyPipe, which I wrote to help render complex pipelines.

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