We are talking about the shell, not some bastardization of execve(), that sees it's not a directly loadable process image so treats it as a script. For those shells implementing shebang as an extension it is still them piping the body of the script after the shebang line, without any token expansion, to an alternate interpreter via an exec() of some sort. Second, conforming applications can not rely on unspecified behaviors, so having a use beyond that specified makes the shell nonconforming. Calling it out like that simply acknowledges a lot of shell implementations choose to make themselves nonconforming, I do not see it as an endorsement or allowance. The requirement explicitly specified behavior shall be implemented as specified takes priority. Some conforming script authors may simply want the first line to be a#!!!! IMPORTANT USAGE NOTE !!!!headline, or similar, not want a utility named "!!!" to be exec'd. What the standard does allow as an extension, and I would support adding to the standard, is adding an option to turn off token expansion in here-doc bodies, and back on, via set. This allows the effect of shebang to be accomplished anywhere in a script, at the expense of a few extra characters for the here delimiter and set commands, without any other changes to tokenizing or the grammar. On Sun, Apr 11, 2021 at 12:15 PM, Harald van Dijk<a...@gigawatt.nl> wrote: On 11/04/2021 17:09, shwaresyst via austin-group-l at The Open Group wrote: > No, it's not nonsense. The definition of comment has all characters, > including '!', shall be ignored until newline or end-of-file being > conforming. Then tokenization which might discover an operator, keyword > or command continues. This precludes "#!" being recognized as any of > those. There is NO allowance for '!' being the second character as > reserved for implementation extensions.
This is wrong on two counts. The first is that you're assuming that this will be interpreted by a shell. If execve() succeeds (and the #! line does not name a shell), it will not be interpreted by a shell at all, and the shell syntax for comments is irrelevant. The second is about what happens when it does get interpreted by a shell: POSIX allows shells to treat files starting with "#!" specially: "If the first line of a file of shell commands starts with the characters "#!", the results are unspecified." Cheers, Harald van Dijk
