Ubuntu – Reverse sed’s/regexes’ pattern-matching priority order

regexsed

Consider this command:

echo "string.with.dots" | sed 's/\(.*\)\.\(.*\)/\1\n\2/'

(Matches into a first capturing group any character until the last . and into a second capturing group any character after it.)

This outputs:

string.with
dots

Reasonably (I think) I tought that using anchors in the right combination would have managed to reverse such behavior (i.e. the match would have been string for the first capturing group and with.dots for the second capturing group), but:

echo "string.with.dots" | sed 's/^\(.*\)\.\(.*\)/\1\n\2/'
echo "string.with.dots" | sed 's/^\(.*\)\.\(.*\)$/\1\n\2/'
echo "string.with.dots" | sed 's/\(.*\)\.\(.*\)$/\1\n\2/'

All output:

string.with
dots

I don't know how the pattern matching is implemented, but it seems that it always privileges the patterns closer to the start of the string rather than those closer to the end of the string (despite any present ^ or missing $).

How can this behavior be changed (i.e. not how to write an hard-coded solution to this example, but how to reverse the pattern-matching priority order into sed or into regexes in general), if possible?

Best Answer

Add two rev and swap \1 and \2:

echo "string.with.dots" | rev | sed 's/\(.*\)\.\(.*\)/\2\n\1/' | rev

Output:

string
with.dots
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