Question

Please have a look at my mind-breaker.

I’d stuck in shrinking with regex some long path, like this:

/12345/123456/1234/123/12/1/1234567/13245678/123456789/1234567890

I’d like to transform this path to the following form:

/123/123/123/123/12/1/123/123/123/123

each “directory” in a path abbreviates to only 3 first characters

LONG_PATH="/12345/123456/1234/123/12/1/1234567/13245678/123456789/1234567890"
perl -pe "s#/(.{1,3})[^/]*?(/|$)#/\1\2#g" <<<$LONG_PATH

/123/123456/123/123/12//1234567/132/123456789/123

sed -E "s#/(.{1,3})[^/]*?(/|$)#/\1\2#g" <<<$LONG_PATH

/123/123456/123/123/12//1234567/132/123456789/123

I have tried also:

perl -pe "s,/(.)(.)?(.)?[^/]*+,/\1\2\3,g" <<<$LONG_PATH
/123/123/123/123/12//123/132/123/123

and many another, no “luck” – I still have no idea about.

Please point me a right way to success.

Answer 1

Match up to three non-slash characters and capture them. Then match the rest until the next slash. Replace by the capture:

"s#(/[^/]{3})[^/]*#\1#g"

There is no need for ungreediness or anything here, because the negated character class is mutually exclusive with the / or $.

EDIT: Although you seem to know this I should probably clarify for future visitors that this will work with either perl -pe... or sed -E... as you have used it in your question. The regex could also be used as is with sed -r.... If you leave out the -E or -r option, then (as usual) you will need to escape both the parentheses and curly brackets:

sed "s#\(/[^/]\{3\}\)[^/]*#\1#g" filename

Note also as ikegami points out that in Perl you should rather use $1 in the replacement than \1.