m4 (GNU M4) 1.4.18 Operating System: Ubuntu 20.04 LTS Kernel: Linux 5.4.0-33-generic Architecture: x86-64
sh$ m4 <<\@
patsubst(`hello', `ll', `XX')
patsubst(`hello', `l+', `XX')
patsubst(`hello', `l\{2\}', `XX')
patsubst(`hello', `l{2}', `XX')
@
heXXo
heXXo
hello
hello
