How to Set variables inside a Linux for loop

Question

I'm trying to determine the existing HDDs in each system using a for loop as show below, the problem is when I try to set the variable using the below code i get sda=true: command not found. What is the proper way to do this?

#!/bin/bash
for i in a b c d e f
do
    grep -q sd$i /proc/partitions
    if [ $? == 0 ]
    then
        sd$i=true
    else
        sd$i=false
    fi
done

declare sd$i=true So there is one catch I have found with this. When I use this in a function, the variable is null outside of the function. How do I get around this? — scharacter
– scharacter, Commented Mar 9, 2011 at 19:20
you would use export in this case. (I have updated my answer.) — mpontillo
– mpontillo, Commented Mar 10, 2011 at 19:42

Dennis Williamson · Accepted Answer · 2011-03-08 20:02:10Z

3

You need to use an array or declare:

declare sd$i=true

answered Mar 8, 2011 at 20:02

Dennis Williamson

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mpontillo · Accepted Answer · 2011-03-10 19:41:42Z

2

I would use an array in this case. For example:

$ i=a
$ sd[$i]=true
$ echo ${sd[a]}
true

As another poster stated, if you want to do this without an array, you can instead make a local variable by using syntax like declare sd$i=true. If you want to make a global variable, use export sd$i=true.

edited Mar 10, 2011 at 19:41

answered Mar 8, 2011 at 20:11

mpontillo

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2 Comments

Dennis Williamson Over a year ago

Unless you're using Bash 4 and associative arrays (declare -A sd), the index will resolve to 0 (unless a is a variable that ultimately resolves to a number). for i in {a..f}; do unset $i; sd[i]=true; done; declare -p sd will result in "declare -a sd='([0]="true")'" (only one element).

mpontillo Over a year ago

@Dennis, thanks for the heads up. (I was testing with bash 4.1.5.)

Ignacio Vazquez-Abrams · Accepted Answer · 2011-03-08 20:02:39Z

0

BASH FAQ entry #6: "How can I use variable variables (indirect variables, pointers, references) or associative arrays?": "Assigning indirect/reference variables"

answered Mar 8, 2011 at 20:02

Ignacio Vazquez-Abrams

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