In script.pl -y goodbye | script.pl -x, the effect of the "|" in the shell command is to provide the STDOUT of the first script as the STDIN of the second script, just as if you'd written:

script.pl -y goodbye >tempfile
script.pl -x <tempfile
[download]

So for this case you don't need to know anything about pipes and IPC, just read from STDIN.

Thank you hv! This is super helpful and resolved my confusion. I was able to write a small test script to do what I need.

Use -p function to check if STDIN is a pipe (to read from standard input for the option; else require an argument for the option) ...

# Some time later, changed the code to collect all the input "do { ...
+ };",
# not just the first line of STDIN.

#!/usr/local/bin/perl

use v5.26; use warnings;

use Data::Dumper qw[ Dumper ];
use Getopt::Long;


my $opt;
GetOptions( 'opt:s' => \$opt )
   or die $!;

say Dumper( { 'Initial, opt' => $opt } );

if ( defined $opt )
{
   if ( -p STDIN )
   {
      say q[Any option argument will be abandoned; collecting STDIN ..
+.];
      # Could process standard input line by line.
      # Here, all is collected at once.
      do { local $/; $opt = <STDIN> };
      say Dumper( { ' ...after collecting STDIN, opt' => $opt } );
   }
   elsif ( $opt eq '' )
   {
      die qq[Neither a value was given for \$opt, nor was specified on
+ standard input.];
   }
   else
   {
      say qq[STDIN is not a pipe; using existing \$opt = $opt.];
   }
}
else
{
   say qq[\$opt was not used, so STDIN was ignored.];
}

say Dumper( { 'Final, opt' => $opt } );
[download]

Later shoved the output of various cases under readmore ...

Thank you parv! Let me try out the -p option. That's very interesting...

Personally I would use the option specification that requires an argument, opt=s (instead of leaving it optional, opt:s, as rot earlier). If the option value would be -, then would switch to reading from standard input unconditionally (without using -p function). That special value of opt would be mentioned in the POD.

I don't smell perl, I smell shell.

If script.pl -y goodbye yields a single string, use backticks:

$ script.pl -x `script.pl -y goodbye`
[download]

If the output of script.pl -y goodbye produces more, and each token is to be processed in turn with script.pl -x, use a loop:

$ for arg in `script.pl -y goodbye`; do script.pl -x $arg; done
[download]

Also, man xargs(1).

If all arguments from perl -y goodbye are to be processed by a single call to perl -x and appear on a single line, have perl -x check @ARGV, probably using Getopt::Std. If they are on multiple lines and piped into script.pl -x, use the -n switch (again, see perlrun), probably checking for the switch -x in a BEGIN block.

This is all I can come up with, given your question. You know, as in "garbage in - garbage out" :)

I would like to use the table output by "script.pl -y goodbye" as the argument of -x.

I believe this is what you want, but I haven't tested it.

script.pl -x `script.pl -y goodbye`
[download]

Right, that would literally be passing the entire table as the argument which is not really intuitive in terms of my script. I thought I could use pipes instead to pass the table, but the underlying script would parse and concatenate the correct column which would then be passed it to the argument of -x. I also want to be able to chain these like all unix commands...

Please read:

• How do I post a question effectively?
• I know what I mean. Why don't you?
• Short, Self-Contained, Correct Example

To help us help you, please create an account ... is new user Konan (created May 07, 2023) our original anonymonk?

See also haukex reply to a later follow-up anonymous post: IO::Select woes

References Added Later

Advice:

• XY Problem by jdporter (2006)
• On Answering Questions by merlyn (2003)
• XYZ Questions by chromatic (2000)

Recent examples of I Know What I Mean Why Don't You:

• Extracting DNC issues by MoodyDreams999 (2023)
• How to find out if an argument is an LVALUE ? (TinyPerl) by harangzsolt33 (2023)

See also:

• Substack OpenMP question: "Here's my bad solution to a problem I haven't described, please fix this bad solution"
• Rubber duck debugging (wikipedia)
• on Debuggers

Updated: Many references were added long after the original node was written.