I have written a script that will only ever run in a linux environment. The purpose of the script is to be piped to, look for certain strings and modify or not and send to STDOUT or not similar to grep/awk/sed but with a more specific purpose that those don't address easily.

I have looked though other posts, but didn't find anything. Not sure if that's because it's impossible, everyone else already knows but me or I just don't know how to search.

I'm trying to determine within the script the context in which it is being executed, and/or better yet, the process/command I'm receiving STDIN from. With my current script, if it runs as in the first example below, it just sits waiting for STDIN and won't exit without CTRL-C or some other non-graceful intervention. When it's receiving STDIN as in the second example, everything works as expected.

For Example:
  • [root@server ~]# script
    • or
  • [root@server ~]# cat myfile | script

    • This is an example of the script logic I'm trying to accomplish:

    #!/usr/bin/perl
use strict;

my @output;
my $stuff;

if ( <not piped to> and @ARGV == 0 ) {
    print "This is how you use this perl script...\n";
    exit;
}

while (<STDIN>) {
    if ($_ =~ m/start/ ) {
        push @output, chomp;
        $stuff = 1;
    } elsif ( $_ =~ m/end/ ) {
        push @output, chomp;
        changout(@output);
        undef $stuff;
    } elsif ($stuff) {
        push @output, chomp;
    } else {
        print STDOUT $_;
    }
    
}

sub changout
{
    foreach my $line (@_) {
        if ( $line =~ m/something/ ) {
            print STDOUT $line;
        } else {
            print STDOUT $line."\n";
        }
    }
}

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    In reply to How do I Determine if my script is being piped to? by netguy

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