Bash if statement behavior

Question

I am missing something fundamental concerning either the bash's if construct/operators or string comparison. Consider the following script:

#!/bin/bash
baseSystem="testdir1"
testme="NA"
if [ "$baseSystem"=="$testme" ]; then
    echo "In error case"
fi
if [ "$baseSystem"!="$testme" ]; then
    echo "In error case"
fi

I get:

In error case
In error case

So it enters each case even though they should be mututally exclusive. Any help is appreciated.

I suggest using '=' instead of '==' for POSIX conformance

mzet
– mzet

2013-06-14 07:30:03 +00:00
Commented Jun 14, 2013 at 7:30 — mzet
– mzet, Commented Jun 14, 2013 at 7:30

devnull · Accepted Answer · 2013-06-14 07:32:15Z

8

bash happens to be somewhat particular about spaces.

Add spaces around the operators:

if [ "$baseSystem" == "$testme" ]; then

...

if [ "$baseSystem" != "$testme" ]; then

The following are not equivalent:

[ "$a"="$b" ]
[ "$a" = "$b" ]

Your first test is essentially the same as saying if [ "testdir1==NA" ]; then which would always be true.

edited Jun 14, 2013 at 7:32

answered Jun 14, 2013 at 7:24

devnull

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