Consider adding -Wexec option of mawk and gawk

[paulapatience]

Consider adding -Wexec option of mawk and gawk

[benhoyt]

I'm open to adding this. However, I don't quite understand the usefulness. Why is it a problem that hyphen-prefixed options are processed by AWK rather than the script? Even the Gawk manual's Executable Scripts section shows a hash bang of #!/bin/awk -f.

And I'm not sure I see what's wrong with the -- approach? Can you help me understand why this is really needed?

If I do add it, I'd prefer just one way to do it. Copying Gawk's -E seems best to me (as GoAWK uses all short options right now).

[paulapatience]

Hopefully the following example is clear. Put the following contents into a file named awc-test.sh:

#!/usr/bin/env bash

read -r -d '' awc <<EOF
BEGIN {
  for (i = 1; i < ARGC; i++) {
    if (ARGV[i] == "--") {
      delete ARGV[i++]
      break
    }
    else if (ARGV[i] !~ /^-./) break
    else if (ARGV[i] == "-c") c = 1
    else if (ARGV[i] == "-w") w = 1
    else if (ARGV[i] == "-l") l = 1
    else printf "awc: unknown option: %s\n", ARGV[i] >"/dev/stderr"
    delete ARGV[i]
  }
  if (!c && !w && !l) c = w = l = 1
}
{ cs += length(); ws += NF; ls++ }
END { printf "%s%s%s\n", l?ls" ":"", w?ws" ":"", c?cs" ":"" }
EOF

printf "#!/usr/bin/env -S mawk -f\n%s\n" "$awc" >mawc-f
printf "#!/usr/bin/env -S gawk -f\n%s\n" "$awc" >gawc-f
printf "#!/usr/bin/env -S awk -Wexec\n%s\n" "$awc" >awc-e
chmod +x mawc-f gawc-f awc-e

run() { echo '$' "$@"; $@; }

run ./mawc-f awc-test.sh
run ./mawc-f -l awc-test.sh
run ./mawc-f -w awc-test.sh
run ./mawc-f -c awc-test.sh
run ./mawc-f -- awc-test.sh
run ./mawc-f -- -l awc-test.sh
run ./mawc-f -- -w awc-test.sh
run ./mawc-f -- -c awc-test.sh

run ./gawc-f awc-test.sh
run ./gawc-f -l awc-test.sh
run ./gawc-f -w awc-test.sh
run ./gawc-f -c awc-test.sh
run ./gawc-f -- awc-test.sh
run ./gawc-f -- -l awc-test.sh
run ./gawc-f -- -w awc-test.sh
run ./gawc-f -- -c awc-test.sh

run ./awc-e awc-test.sh
run ./awc-e -l awc-test.sh
run ./awc-e -w awc-test.sh
run ./awc-e -c awc-test.sh
run ./awc-e -- awc-test.sh
run ./awc-e -- -l awc-test.sh
run ./awc-e -- -w awc-test.sh
run ./awc-e -- -c awc-test.sh

and run it (mawk and gawk must be in PATH, and awk must refer to one of the two). The result is the following:

$ ./mawc-f awc-test.sh
55 239 1387 
$ ./mawc-f -l awc-test.sh
mawk: not an option: -l
$ ./mawc-f -w awc-test.sh
mawk: not an option: -w
$ ./mawc-f -c awc-test.sh
mawk: not an option: -c
$ ./mawc-f -- awc-test.sh
55 239 1387 
$ ./mawc-f -- -l awc-test.sh
55 
$ ./mawc-f -- -w awc-test.sh
239 
$ ./mawc-f -- -c awc-test.sh
1387 
$ ./gawc-f awc-test.sh
55 239 1387 
$ ./gawc-f -l awc-test.sh
gawk: fatal: cannot open shared library `awc-test.sh' for reading: No such file or directory
$ ./gawc-f -w awc-test.sh
239 
$ ./gawc-f -c awc-test.sh
55 239 1387 
$ ./gawc-f -- awc-test.sh
55 239 1387 
$ ./gawc-f -- -l awc-test.sh
55 
$ ./gawc-f -- -w awc-test.sh
239 
$ ./gawc-f -- -c awc-test.sh
1387 
$ ./awc-e awc-test.sh
55 239 1387 
$ ./awc-e -l awc-test.sh
55 
$ ./awc-e -w awc-test.sh
239 
$ ./awc-e -c awc-test.sh
1387 
$ ./awc-e -- awc-test.sh
55 239 1387 
$ ./awc-e -- -l awc-test.sh
awk: ./awc-e:15: fatal: cannot open file `-l' for reading: No such file or directory
$ ./awc-e -- -w awc-test.sh
awk: ./awc-e:15: fatal: cannot open file `-w' for reading: No such file or directory
$ ./awc-e -- -c awc-test.sh
awk: ./awc-e:15: fatal: cannot open file `-c' for reading: No such file or directory

Without -Wexec, it is impossible to mimic the command-line interface of wc, or to write a script that behaves like a conventional command-line utility. -- is required to stop the Awk interpreter from parsing options, but then supposing you wanted to stop processing options in the script itself, you'd need a second --. Using awk -f in the hashbang line leaks the fact that the script is written in Awk. If you wanted to rewrite the script in another language (e.g., Go), the command-line interface would have to change (or remain unnatural).

As for providing -E only, your reasoning makes sense. It would be trivial to update by Makefile an Awk script's hashbang line to use -E rather than -Wexec. At least it wouldn't require a wrapper shell script.

Note that providing options to the Awk interpreter is always possible even with -E by explicitly invoking awk -f. So nothing is lost by using -E in the hashbang line.

[benhoyt]

Thanks for the additional justification and examples. I understand this now and think it makes sense. I've added this in #140 and will merge and tag a release in the next few days -- let me know what you think!

[benhoyt]

Thanks @paulapatience -- just tagged and released v1.20.0 with this feature.