Best way to test perl -pi -e one-liner before execution?

Question

I don't know any Perl, but I do occasionally use "perl pie" (perl -pi -e) to do a batch regex find and replace, e.g. change a to e in all the .txt files in a folder perl -pi -e 's|a|e|g' *.txt.

Is there any way to do a "dry run" so that I can preview the change? I'm frequently using moderately complex regexes with positive / negative lookaheads / lookbehinds, group references, etc., and I'm often not 100% sure I have it right on the first run. It would be wonderful to have something like rename.pl's -n flag, which doesn't change anything, only outputs the changes that would have been made.

Currently, my strategy is to just use ack, which accepts a Perl regex, to make sure my match string is correct, and go from there. Is there a better way? Anything like rename -n?

Also open to something other than perl if I'm missing something awesome, though I am partial to its regex format.

Many thanks!

Answer 1

Just remove the -i parameter from your perl code to do a dry run.

perl -pe 's|a|e|g' *.txt

From perl --help,

-i[extension]     edit <> files in place (makes backup if extension supplied)

To print the particular line where the replacement occurs.

$ cat file
abcd
cbcb
foo
$ perl -nle 'print if s|a|e|g' file
ebcd