Regex to find string arguments of a function call (lookbehind with multiple hits)

Question

I want to use grep (PCRE) to find all single-quoted strings that are passed to my function foo().

Example functions calls in my source code and the expected hits:

foo('Alice')                    -> Expected Hits: Alice
foo('Alice', 'Bob', 'Charlie')  -> Expected Hits: Alice, Bob, Charlie
foo(flag ? 'Alice' : 'Bob')     -> Expected Hits: Alice, Bob

My regex:

foo\([^\)]*\K(?:')([^'\)]*)(?:'\))

However, I get only the last single-quoted string for each function call and not all as you can see in my regex101 playground: https://regex101.com/r/FlzDYp/1

How can I define a PCRE conform regex for grep to get all expected hits?

Answer 1

You might use grep with -P for PCRE and -o to print only the matched parts.

The pattern in parts matches:

• (?: Non capture group
  • \bfoo\( Match the word foo followed by (
  • (?=[^()]*\)) Positive lookahead to assert a closing ) to the right
  • | Or
  • \G(?!^) Assert the current position at the end of the previous match, but not at the start of the string (as \G can match at those 2 positions)
• ) Close the non capture group
• [^']* match optional chars other than '
• (?:'\h*[,:]\h*)? Optionally match either , or : between optional spaces
• ' Match the '
• \K Forget what is matched so far as we don't want that ' in the result
• \w+ Match 1 or more word characters

Example:

grep -oP "(?:\bfoo\((?=[^()]*\))|\G(?!^))[^']*(?:'\h*[,:]\h*)?'\K\w+" file

See a regex demo for the matches.

---

An alternative using awk first matching the format foo(....) and then printing all the values between the single quotes that are alphanumeric or an underscore using a while loop.

The \047 is a single quote here.

awk '/foo\([^][]*\)/ {
  while(match($0, /\047[[:alnum:]_]+\047/)) {
    print substr($0, RSTART+1, RLENGTH-2)
    $0 = substr($0, RSTART + RLENGTH)
  }
}' file

Answer 2

In JavaScript, we can match all function calls, then use match a second time to find all string parameters:

var input = `foo('Alice')
foo('Alice', 'Bob', 'Charlie')
foo(flag ? 'Alice' : 'Bob')`;

var calls = Array.from(input.matchAll(/foo\((.*?)\)/g));
var arguments = calls.map(call => Array.from(call[1].matchAll(/'(.*?)'/g)));
for (var i=0; i < calls.length; ++i) {
    console.log(calls[i][0] + ": " + arguments[i].map(argument => argument[1]));
}