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I was thinking of unorthodox uses for the shebang, and realized cat gives you a very succinct quine. Any other funny commands? ls -l is cool too.

• philh 10y ago
  Ages ago I wrote a simple command that let you do shell scripting in the shebang line. http://reasonableapproximation.net/2010/07/27/silly-things-to-do-with-shebang-lines.html http://reasonableapproximation.net/2010/07/27/silly-things-t... I'm not sure I've used it since, but I still like the xgraph thing.
  • jmiserez 10y ago
    Very interesting and a good read. I was not aware that you could pass an argument in the shebang line.
    • hk__2 10y ago
      It’s often used to have your shell scripts fail fast by using `#! /usr/bin/bash -e`; which you could also do by using `set -e` at the beginning of the script but that’s less elegant.
  • kylek 10y ago
    This is pretty great little read, much appreciated
• gkya 10y ago
  #!/bin/rm #!/sbin/md5 #!/usr/bin/file #!/usr/bin/du -h And yet another quine: #!./quine cat $0 Edit: I was not sure about #!/sbin/poweroff, and I cannot try now, so removed.
  • cyphar 10y ago
    I'm fairly sure `#!./quine` will cause an error because there's a limit of 5 recursive checks to find the interpreter of a script (fs/binfmt_script.c).
    • gkya 10y ago
      Ran it, works. I'm on freebsd 10.3 BTW.
      • cyphar 10y ago
        On Linux you get ELOOP. How does that resolution even work on FreeBSD? Why does it resolve to $SHELL (the file resolves to itself).
        • usmannk 10y ago
          Yeah, I don't see that working unless the shebang is changed to `#!/bin/sh`?
        • gkya 10y ago
          execve(2) on my machine defines ELOOP lie this: Too many symbolic links were encountered in translating the pathname. Refer to sys/kern/imgact_shell.c and ^do_execve in sys/kern/kern_exec.c, I skimmed but could not find why it ran.
          • cyphar 10y ago
            Presumably then, whatever shell you're using decides to just execute the code as a subshell rather than use execve(2). Can you dtrace it to figure out whether it actually calls execve(2)?
            • gkya 10y ago
              After running dtrace as $ sudo dtrace -n 'syscall::execve*:entry { printf("%s %s", execname, copyinstr(arg0)); }' I had this output 0 51617 execve:entry sh ./quine 1 51617 execve:entry sh /bin/sh 1 51617 execve:entry sh /bin/cat Altho this is the first time I use dtrace. I can try to run another command you can ask me to. My login shell is the Bourne shell. However I tried bash, csh and tcsh too, it works, so it's probably the system level code that substitutes /bin/sh (maybe because it's my login shell?) to the interpreter.
  • djsumdog 10y ago
    Huh...yea, I never though about how the first argument to a program is always itself.
  • Null-Set 10y ago
    rm, with self cleaning action!