The inner `.*\s+` in `(?:[A-Za-z_][A-Za-z0-9_]*=.*\s+)*` creates
catastrophic backtracking because both `.*` and `\s+` can match
whitespace. When the exec tool processes commands with `VAR=value`
assignments followed by whitespace-heavy text (e.g. HTML heredocs),
the regex engine hangs permanently at 100% CPU.
Replace `.*` with `\S*` in all three instances. Shell prefix variable
assignments cannot contain unquoted whitespace in the value, so `\S*`
is semantically correct and eliminates the ambiguity.
Fixes#61881
eede8f945f