Using shift in bash

KG425 · 06-04-2012, 03:20 PM

Hello,

I have a quick question. Suppose I do the following:

Code:

set 1 2 3 4 5
a=''
for i in "$@"; do
    if [ $i = '2' ]; then
        shift
        a=$i
    fi
done

After doing it, I want a to have value of 3 but instead I get 2 which is not what I want. Please help me.

bigrigdriver · 06-04-2012, 06:30 PM

$i = '2' indicates value assignment.

$i == '2' indicates equality.

grail · 06-05-2012, 02:19 AM

@bigrigdriver - actually, either is applicable in bash. Although I do personally prefer == from a visual perspective.

You appear to be confusing parameters with the value stored in your variable. Shift has no affect on "i" but rather on the parameters.
So when $i is equal to 2, it never stops being equal to 2. Also, as you are comparing numbers you should either use -eq for the test or the more
preferred (()) when testing numbers.

So I would suggest something like:

Code:

#!/bin/bash

while (( $# ))
do
    if (( $1 == 2 ))
    then
	shift
	a=$1
    fi
    shift
done

echo $a