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Comment by pbhjpbhj | Hacker News Reader

Aside:

What do you mean by "use a symbolic link" (I'm familiar with `ln -s` fwiw) the alias carries the command switch, how do you do that with a link?

    # example
    alias egrep='grep -E'

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Currently, egrep and fgrep are shell scripts (the too-simple version of this idea would be

  #!/bin/sh
  exec /usr/bin/grep -E "$@"

but that would mess up help messages and probably also needs disaster handling in case exec fails). Another traditional way, however, is to symlink everything to a single binary, which uses argv[0] or getprogname() to see which name the user called it under and acts accordingly. In the extreme case, you get the "multi-call binaries" Busybox or Toybox, which contain an entire set of Unix utilities in a single (not-too-slim) executable image. GNU grep also used that technique at some point in its history, but it was discarded for a reason I don't recall.

Actually it turns out that, at least in debian 11, you were right on the money:

    cat `which egrep`
    #!/bin/sh
    exec grep -E "$@"

But I agree that it would be cleaner and trivial to implement this behavior by depending on argv[0], GNU style guide be damned.

You use argv0 to check the program name. The utility has to support it in code which GNU apparently dislikes as someone mentioned elsewhere in the thread.

A program like "grep" gets the path to the binary in argv[0], if it sees that argv[0] is something like

   /some/path/fgrep

it adds the -E flag. A hard link works OK too, as done copying the whole binary.

This is not the case for GNU grep. It appears only some BSDs do this.

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