Title: Using boolean variables in Bash Date: 2009-01-06 17:27 Author: aperez Category: Igalia Tags: bash
Today I stumbled upon a weblog post by Mark Dominus on a “novel” way of using flag variables in shell code, mainly because I have been using that technique since my early days of shell programming. Let me introduce the syntax:
the_world_is_flat=true
# ...do something interesting...
if $the_world_is_flat ; then
echo 'Be careful not to fall off!'
fi
This example may look familiar to some of my readers, because in fact it
is taken from the Bill tutorial. Some modules included in Bill
use this kind of syntax extensively. Some care must be taken, because we
are directly executing the contents of a variable in the if clause, so
you would not better use this with values entered by the user, but I
find very convenient to directly expand and evaluate true and false
from variables when they come from “trusted” code.
I learned this trick several years ago from my friend Andrés when we were working together. I do not know when did he learn this syntax, but I am sure that the thing is not as new as it sounds.
Oops, almost forgot: have a nice 2009!