3 ms·

Some advanced bash scripting

10 points by jdorfman 10y ago

robinhoodexe 10y ago
Interesting, but a whole lor shorter than what I expected to be honest.
Xophmeister 10y ago
This is kind of lacking in content for something claiming to be "advanced", to say the least. "Defensive BASH programming"[1], which has been featured on HN before, contains a lot more useful advice. Personally, I would also recommend using ShellCheck[2] to lint your scripts. [1] http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-programming/ http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-progr... [2] https://www.shellcheck.net/ https://www.shellcheck.net/
- jdorfman 10y ago
  These are great resources, thank you.
joatmon-snoo 10y ago
Also, set -e is not a good flag to rely on, because it can really trip you up if you do anything at all that involves subshells, e.g.: set -e function foo { false echo foo } i=1 while [[ i -le 20 ]]; do echo "$i $(foo)" i=$((i+1)) done
cosmie 10y ago
The first example has a lot more use cases than it alludes to. I have a lot of aliased utility scripts for text processing, and frequently need to use them over entire files as well as on output piped from other processes. In this case, I don't know if the input file is going to be an argument or stdin from some upstream operation. That's easily taken care of with INPUT_FILE="${1:-/dev/stdin}" Which sets the input to the first argument if there is one, or stdin if there isn't. My solution was a lot messier before I learned about parameter substitution.
prairiedock 10y ago
It's not advanced, it's not long enough, and it's not correct either. > This will set the value of TMP to `/tmp/myproject` only if it has not been set. This should read "if", not "only if". And it should read: "This will set the value of TMP to `/tmp/myproject` if it has not been set or if it is null." The form that means 'if it has not been set' has no colon; it is TMP=${TMP-/tmp/myproject} See https://www.gnu.org/software/bash/manual/bash.html#Shell-Parameter-Expansion https://www.gnu.org/software/bash/manual/bash.html#Shell-Par...

10 points by jdorfman 10y ago

Interesting, but a whole lor shorter than what I expected to be honest.

This is kind of lacking in content for something claiming to be "advanced", to say the least. "Defensive BASH programming"[1], which has been featured on HN before, contains a lot more useful advice. Personally, I would also recommend using ShellCheck[2] to lint your scripts. [1] http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-programming/ http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-progr... [2] https://www.shellcheck.net/ https://www.shellcheck.net/

jdorfman 10y ago
These are great resources, thank you.

joatmon-snoo 10y ago

Also, set -e is not a good flag to rely on, because it can really trip you up if you do anything at all that involves subshells, e.g.: set -e function foo { false echo foo } i=1 while [[ i -le 20 ]]; do echo "$i $(foo)" i=$((i+1)) done

cosmie 10y ago

The first example has a lot more use cases than it alludes to. I have a lot of aliased utility scripts for text processing, and frequently need to use them over entire files as well as on output piped from other processes. In this case, I don't know if the input file is going to be an argument or stdin from some upstream operation. That's easily taken care of with INPUT_FILE="${1:-/dev/stdin}" Which sets the input to the first argument if there is one, or stdin if there isn't. My solution was a lot messier before I learned about parameter substitution.

prairiedock 10y ago

It's not advanced, it's not long enough, and it's not correct either. > This will set the value of TMP to `/tmp/myproject` only if it has not been set. This should read "if", not "only if". And it should read: "This will set the value of TMP to `/tmp/myproject` if it has not been set or if it is null." The form that means 'if it has not been set' has no colon; it is TMP=${TMP-/tmp/myproject} See https://www.gnu.org/software/bash/manual/bash.html#Shell-Parameter-Expansion https://www.gnu.org/software/bash/manual/bash.html#Shell-Par...