#!/usr/bin/perl

# https://perlmonks.org/?node_id=1226189

use strict;
use warnings;

while( <DATA> )
  {
  if( /\|([^|,]*(?:,[^|,]*)+)\|/ )
    {
    print "$`|$_|$'" for split /,/, $1;
    }
  else
    {
    print;
    }
  }

__DATA__
 some text FOO | some text BAR | oh , no , commas | some text BAZ | so
+me text QUX
 some text FOO | some text BAR | single | some text BAZ | some text QU
+X
[download]

Outputs:

 some text FOO | some text BAR | oh | some text BAZ | some text QUX
 some text FOO | some text BAR | no | some text BAZ | some text QUX
 some text FOO | some text BAR | commas | some text BAZ | some text QU
+X
 some text FOO | some text BAR | single | some text BAZ | some text QU
+X
[download]