How do I match text only when it is followed by a specific pattern using zero-width lookahead?

Explanation

Vim's regex engine supports zero-width positive lookahead via the \@= operator. The syntax is main_pattern\(lookahead\)\@=: place the lookahead pattern inside a group and append \@=. The search matches only when the main pattern is immediately followed by the lookahead — the lookahead itself is not consumed or included in the matched text, leaving the cursor at the end of main_pattern.

How it works

• Place the lookahead pattern in a captured group: \(lookahead_pattern\)
• Append \@= to make the group match zero-width
• Full form: what_to_match\(what_must_follow\)\@=

\@= is the Vim equivalent of Perl's (?=pattern) positive lookahead.

Example

Given text:

print("hello")
println("world")
echo "hi"

Find print only when directly followed by (:

/print\(([)\@=

This matches print in print("hello") but not in println("world"), where print is followed by l, not (.

Tips

• Negative lookahead \@!: match when NOT followed by a pattern — e.g., foo\(bar\)\@! finds foo not followed by bar
• Positive lookbehind \@<=: match when preceded by a pattern — e.g., \(foo\)\@<=bar finds bar only when preceded by foo
• Negative lookbehind \@<!: match when NOT preceded by a pattern
• Combine with \zs and \ze to control which part of the match is highlighted or used in substitutions