regex in sed

Question

Hi.

I need to use sed to convert all occurences of ##XXX## to ${XXX}. X could be any alphabetic character or '_'. I know that I need to use something like:

's/##/\${/g'

But of course that won't properly, as it will convert ##FOO## to ${FOO${

Any takers? - Don

Answer 1

Use this:

s/##\([^#]*\)##/${\1}/

BTW, there is no need to escape $ in the right side of the "s" operator.

Answer 2

sed 's/##\([a-zA-Z_][a-zA-Z_][a-zA-Z_]\)##/${\1}/'

The \(...\) remembers...and is referenced as \1 in the expansion. Use single quotes to save your sanity.

As noted in the comments below this, this can also be contracted to:

sed 's/##\([a-zA-Z_]\{3\}\)##/${\1}/'

This answer assumes that the example wanted exactly three characters matched. There are multiple variations depending on what is in between the hash marks. The key part is remembering part of the matched string.

Answer 3

Here's a shot at a better replacement regex:

's/##\([a-zA-Z_]\+\)##/${\1}/g'

Or if you assume exactly three characters :

's/##\([a-zA-Z_]\{3\}\)##/${\1}/g'

Answer 4

echo '##XXX##' | sed "s/^##([^#]*)/##${\1}/g"