[JonChesterfield]

Sed confuses me more than awk but you're right. That would also remove the only use of awk in my makefile (sed is there already for hacking around spaces in filenames).

Whitespace padding output in sed is probably horrible, column looks simpler than printf via bash or trying to use make's $info.

[defrost]

Whilst acknowledging that "Confused by SED" has overlap with "have used SED for 40 years and have three books purely on SED" I can recommend

https://www.grymoire.com/Unix/Sed.html

as a reference some might occasionally swear by.

    Anyhow, sed is a marvelous utility. Unfortunately, most people never learn its real power. The language is very simple, but the documentation is terrible. The Solaris on-line manual pages for sed are five pages long, and two of those pages describe the 34 different errors you can get. A program that spends as much space documenting the errors as it does documenting the language has a serious learning curve.

[JonChesterfield]

Appreciated, reading through it. I suspect the majority of the sed experience can be attributed to it using "posix regular expressions" by default. It was about a decade after first discovering sed that I realised passing -E was really important.

It is difficult for newcomers to guess that "extended regular expressions" refers to the barely-usable subset of "regular expressions" and "posix regular expressions" are terrible in comparison to either.

edit: alright, yes, one can program in that. Sed can recurse.

  .PHONY: help3
  help3:
   sed -nE 's/^([a-zA-Z_*.-]+):.*## (.*)$$/\1 :\2/ p' \
   $(MAKEFILE_LIST) | \
   sed -E -e ':again s/^([^:]{1,16})[:]([^:]+)$$/\1 :\2/ ' -e 't again '  |\
   sed -E 's/^([^ ]*)([ ]*):(.*)$$/\1:\2\3/' |\
   sort

The first invocation filters out the lines of interest, second one space pads to 16. That works by putting the colon before the help text and repeatedly inserting a space before the colon until there are at least sixteen non-colon characters in the first group.

Composing the -n/p combination with act on everything is a stumbling block for merging the multiple invocations together but I expect it to be solvable.

[JonChesterfield]

After a slightly dubious use of time, I can confirm that columns is not necessary. Also noticed that the original version missed double_colon:: style targets. I fear sort is not necessary either but one has to draw the line somewhere.

  HELP_PADDING := 30
  
  .PHONY: awkhelp
  awkhelp: ## Write this help using awk
   @echo "awkhelp:"
   @awk 'BEGIN {FS = ":.*#+"}; /^[a-zA-Z_*.-]+:.*## .*$$/ {printf "  %-'$(HELP_PADDING)'s %s\n", $$1, $$2}' \
   $(MAKEFILE_LIST) | \
   sort
  
  .PHONY: sedhelp
  sedhelp: ## Write this help using sed
   @echo "sedhelp:"
   @sed -E \
   -e '/^([a-zA-Z_*.-]+::?[ ]*)##[ ]*([^#]*)$$/ !d # grep' \
   -e 's/([a-zA-Z_*.-]+:):?(.*)/  \1\2/ # drop :: and prefix pad' \
   -e ':again s/^([^#]{1,'$(HELP_PADDING)'})##[ ]*([^#]*)$$/\1 ##\2/ # insert a space' \
   -e 't again # do it again (termination is via {1, HELP_PADDING})' \
   -e 's/^([^#]*)##([^#]*)$$/\1\2/ # remove the ##' \
   $(MAKEFILE_LIST) | \
   sort