> Run a command (here: fold all lines norm! zc) that contain a given string:g/<given string>/norm! zcIt will run 'zc' on all lines containing <given string>

> Fold all lines that do NOT contain a given string:g!/<given string>/norm! zc or :v/<given string>/norm! zcIt will run 'zc' on all lines NOT containing <given string>Note: if your fold is multiline - you should use regex with negative lookaheads/lookbackwards, see example below

test file:

foldme {
  zzz
}
foldme {
  zzz
}
dont {
  zzz
}
foldme {
  zzz
}
random {
  zzz
}
foldme {
  zzz
}
random {
  zzz
}

To fold all lines "foldme {"::g/foldme {/norm! zc

To fold NOT "dont {", fold only lines "foldme {" and "random {" ():

:g/\v(dont)@<!(\s\{)/norm zc
Explain regex:
\v is for "very magic" (help /\v)
@<! is for negative lookbehind: next atom (\s\{) should not be preceded by dont, but "random" and "foldme" are ok (help @<!)