til/sed/reference-the-full-match-in-the-replacement.md

Reference The Full Match In The Replacement

The & can be used in the replacement part of a sed expression as reference to the string match for this iteration of the expression. The occurrence of & will be replaced with that entire match.

As the sed man page puts it:

An ampersand (“&”) appearing in the replacement is replaced by the string matching the RE.

I made use of this recently with a sed expression that was evaluating a list of filenames that I wanted to construct into a sequence of mv commands. I needed the filename that I was matching on to appear as the first argument of the mv command I was constructing.

Here is what that looks like:

$ ls *.pdf |
  sed 's/\(..\)\(..\)\(..\) Statement\.pdf/mv "&" "20\3-\1-\2-statement.pdf"/'

Notice right after mv in literal quotes is the &. That will be replaced in the resulting replacement with the full matching string of the regular expression in the first part of the sed statement (s/<RE>/).