Bash Scripting Arrays

Question

I'm trying to read command line arguments through a bash scripts and am having difficulties getting desired results. I want to read in two parameters, one after -var1 and one after var2.

I am passing in these arguments

-var1 hello -var2 world

args=("$@") x="0" for (( i=0;i<$#; i++ )) do x=$(($x + 1)) echo " $i $x " if [[ ${args[${i}]} == "-var1" ]] ; then if [ $# > $x ] ; then var1="${args[${i+1}]}" fi fi echo $i if [[ ${args[${i}]} == "-var2" ]] ; then if [ $# > $x ] ; then var2="${args[${i+1}]}" fi fi done

It sets both variables, var1 and var2, equal to hello, rather than var1="hello" and var2="world". Any thoughts? Thanks in advance

What are -fef and -scripts then? Also, $x doesn't seem necessary, especially since it is always just $i+1. — chepner
– chepner, Commented Aug 19, 2014 at 18:45
I have previously looked at that code, and I understand that is an alternate way to do it. I am still unsure why the above code does not work, which is why I asked the question. — randydalton411
– randydalton411, Commented Aug 19, 2014 at 18:48

konsolebox · Accepted Answer · 2014-08-19 19:26:07Z

Try doing it this way instead:

#!/bin/bash while [[ $# -gt 0 ]]; do case "$1" in -var1) var1=$2 shift ;; -var2) var2=$2 shift ;; *) echo "Invalid argument: $1" exit 1 esac shift done if [[ -z $var1 ]]; then echo "Var1 was not specified." exit 1 fi if [[ -z $var2 ]]; then echo "Var2 was not specified." exit 1 fi ... do something with var1 and var2

glenn jackman · Accepted Answer · 2014-08-19 21:18:06Z

I agree with konsolebox.

Your code is suffering from excessive variable bracing. ${i+1} will not actually perform the addition. The expression within [] in an array expansion is evaluated as an arithmetic expression. Try this:

args=("$@") for (( i=0; i<$#; i++ )) do [[ ${args[i]} == "-var1" ]] && var1=${args[++i]} [[ ${args[i]} == "-var2" ]] && var2=${args[++i]} done echo "var1='$var1'" echo "var2='$var2'"

output

var1='hello' var2='world'

We could get more dynamic about it:

args=("$@") for (( i=0; i<$#; i++ )); do [[ ${args[i]} == -* ]] && declare ${args[i]#-}=${args[++i]} done

or even

while (( $# > 0 )); do [[ $1 == -* ]] && { declare ${1#-}=$2; shift; } shift done

dganesh2002 · Accepted Answer · 2014-08-19 21:55:40Z

Use getopts ->

while getopts "a:b:" flag do case "$flag" in a) echo "var1=$OPTARG" ;; b) echo "var2=$OPTARG" ;; *) echo "Incorrect Usage" ;; esac done

Then run it as -a "hello" -b "world"

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