How can I use a look after to match either a single or a double quote?

Question

I have a series of strings I want to extract:

hello.this_is(\"bla bla bla\")
some random text
hello.this_is(\'hello hello\')
other stuff

What I

Answer 1

Based on revo and hek2mgl excellent answers, I ended up using grep like this:

grep -Po '(?<=hello\.this_is\((["'\''])).*(?=\1)' file

Which can be explained as:

• grep
• -Po use Perl regexp machine and just prints the matches
• '(?<=hello\.this_is\((["'\''])).*(?=\1)' the expression
  • (?<=hello\.this_is\((["'\''])) look-behind: search strings preceeded by "hello.this_is(" followed by either ' or ". Also, capture this last character to be used later on.
  • .* match everything...
  • (?=\1) until the captured character (that is, either ' or ") appears again.

The key here was to use ["'\''] to indicate either ' or ". By doing '\'' we are closing the enclosing expression, populating with a literal ' (that we have to escape) and opening the enclosing expression again.