Why is '$_' the same as $ARGV in a Perl one-liner?

Question

I ran into this problem while trying to print single quotes in a Perl one-liner. I eventually figured out you have to escape them with \'\\\'\'. Here\'s some code t

Answer 1

You use single quotes in one-liners to protect your Perl code from being evaluated by the shell. In this command:

perl -ne 'chomp; print "'$_'\n"' shortlist.txt

you close the single quotes before $_, so the shell expands $_ to the last argument to the previous command. In your case, this happened to be the name of your input file, but the output would be different if you ran a different command first:

$ echo foo
$ perl -ne 'chomp; print "'$_'\n"' shortlist.txt
foo
foo
foo
foo
foo