perl query using -pie

Question

This works:

perl -pi -e \'s/abc/cba/g\' hellofile

But this does not:

perl -pie \'s/cba/abc/g\' hellofile

Answer 1

The -i flag takes an optional argument (which, if present, must be immediately after it, not in a separate command-line argument) that specifies the suffix to append to the name of the input file for the purposes of creating a backup. Writing perl -pie 's/cba/abc/g' hellofile causes the e to be taken as this suffix, and as the e isn't interpreted as the normal -e option, Perl tries to run the script located in s/cba/abc/g, which probably doesn't exist.