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StringReplaceFirst

Function StringReplaceFirst( const S, OldPattern, NewPattern : string) : string

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := StringReplaceFirst('North NORTH north', 'north', 'South');
  // South NORTH north
end;

Usage​

StringReplaceFirst replaces the first non-overlapping occurrence of a pattern using case-insensitive Velox string comparison.

Important behavior and quirks

  • Matching is always case-insensitive; there is no flag for a case-sensitive first replacement.
  • Empty source or empty old pattern is returned unchanged.
  • The first match is determined from the beginning of the source. Later occurrences remain exactly as supplied.
  • OldPattern is literal text, not a regex or wildcard expression.
  • NewPattern can be empty to delete the first match.
  • Non-ASCII ignore-case results can depend on Velox's current locale/case-conversion behavior.
  • Embedded NUL remains part of the length-counted source.

Additional Technical Info​

StringReplaceFirst replaces only the earliest case-insensitive occurrence of OldPattern in S. It returns a new string and leaves the input unchanged.

The example is fictional and source-reviewed only.

How it works

The wrapper calls Delphi StringReplace(S, OldPattern, NewPattern, [rfIgnoreCase]). Because rfReplaceAll is absent, scanning stops after the first match.

Performance and concurrency

At most one match is replaced, although the search still scans up to that match. Output allocation depends on the replacement length. The function mutates no Velox state.

External references

Created 2026-07-15