Terminate Bash script dependent on piped output

I have written the following shell script:

#!/bin/bash


counter=0

while [ $counter -lt 250 ]; do
        perl Cumulative_Percentage.pl TP53.lst T1_endo.maf >> OutFile
        perl Optimize_Panel.pl TP53.LST T1_endo.maf >> TP53.lst 
        let counter=counter+1
done

And it works well. The problem is that it often runs through far more loops than it needs to. The Perl script, Optimize_Panel.pl, prints a single line if the loop should continue or exits without printing if the loop should stop. I want the while loop to terminate if Optimize_Panel.pl exits instead of printing... but how?

One possible solution I can imagine is to run

wc TP53.lst

at the beginning and end of the loop; first setting it to a variable then checking to see if it had increased then leading it to a premature done statement if TP53.lst had not been appended. I'm confident that this could work but it feels clunky and I suspect there is a much simpler way to modify the shell script.

Another way I can think of doing this would be to pipe the output of Optimize_Panel.pl into a temporary file then somehow check to see if that file was empty.

Any ideas?

Solution

You can capture the output in a variable, then break out of the loop if that variable is zero-length.

while [ $counter -lt 250 ]; do
    perl Cumulative_Percentage.pl TP53.lst T1_endo.maf >> OutFile
    output=$(perl Optimize_Panel.pl TP53.LST T1_endo.maf)
    [ -z "$output" ] && break
    echo "$output" >> TP53.lst 
    let counter=counter+1
done