Question

So, let’s say I have the strings:

aaa -Dprop=var Class arg
aaa Class arg

I want a single one-liner (perl, sed, awk, doesn’t matter) that can extract arg and var (if its there). Specifically, I’d like to return

arg var
arg

The following works for the first one:

echo "aaa -Dprop=var Class arg" | perl -pe 's|.*(-Dprop=([a-z]*)).*Class (.*)|\3 \2|'

but because -Dprop= is required, it obviously doesn’t work the second one.

If, however, I make that match optional:

echo "aaa -Dprop=var Class arg" | perl -pe 's|.*(-Dprop=([a-z]*))?.*?Class (.*)|\3 \2|'

it doesn’t work for the first one because, I believe the two .*s are greedy qualifiers and match -Dprop first.

If I make them non-greedy, it still doesn’t work, but I’m not sure why.

echo "aaa -Dprop=var Class arg" | perl -pe 's|.*?(-Dprop=([a-z]*))?.*?Class (.*)|\3 \2|'

So, first, what regex can I use that matches correctly? (I know I could split it into multiple commands, but I rather just have one).

Answer 1

Perhaps:

echo "aaa -Dprop=var Class arg"|perl -pe 's|(.*-Dprop=(.*))?.*Class\s*(.*)|$3 $2|'

Notice too that \3 is better written as $3 (which the warnings pragma would divulge).