How to Debug Bash Scripts | Hacker News Reader

How to Debug Bash Scripts

aymanh.com

55 pointskirubakaran7 comments

I always like this approach for dangerous (almost anything which messes with files is dangerous ;) ) scripts: output the commands it would execute, but don't execute them. The user can eyeball them and check that those commands are what he wants and copies them into a shell toe xecute them.

also, "set -o xtrace" is quite helpful

Why do they always focus on bash (or mysql, or php, or whatever).

90% of the article is applicable for other shells, like zsh or fish.

Why not write "how to debug shell scripts"?

I almost exclusively use bash. Not because of a particular love of bash, but just because that's the default install on Linux (and even OSX). Consequently, I don't know what the real differences are between bash and other shells.

It's possible the author is like me: because he's not familiar with what the differences between the shells are, he can't say what does and does not apply to other shells.

The differences:

  * zsh has a ton of interactive chrome built-in, and a lot of it is on by default.
      This leads to some incompatibility with bash for scripting purposes
      the contextual completion stuff is infuriating when it's overly restrictive
  
  * A pure bourne shell (like dash) by nature doesn't support bashisms
      like $() as an alternative to ``
      On almost all gnu systems /bin/sh is a link to bash 
        which checks $0 and operates in sh mode
      Unfortunately bash's sh mode is completely broken
        it allows most bash-specific syntax
        so almost a lot of Linux users's #!/bin/sh scripts really need bash

The takeaway is that you should give up and use bash, or write your own shell if you're an asshole (I have done this).

Command substitution using $(...) is valid POSIX syntax, not a bashism.

   $ /bin/dash
   $ echo $(uname -r)
   2.6.31-rc7

or write your own shell if you're an asshole

Eshell.

It is nice to write "shell scripts" like "(loop for i in *.el do (byte-compile-file i))".

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