Bash string comparison of two identical strings false?

Question

Hello I have the following script:

#! /bin/bash
 Output=$(defaults read com.apple.systemuiserver menuExtras | grep Bluetooth.menu)
Check="\"/System/Library/CoreServices/Menu Extras/Bluetooth.menu\","
echo $Output
echo $Check
     if [ "$Output" = "$Check" ]
    then
           echo "OK"
else
    echo "FALSE" 
    echo "Security Compliance Setting 'Show Bluetooth Status in Menu Bar(2.1.3)' has been changed!" | logger

fi

When you run it, both variables have the exact same output however the check always says it is FALSE

here is the out put from my terminal:

"/System/Library/CoreServices/Menu Extras/Bluetooth.menu",
"/System/Library/CoreServices/Menu Extras/Bluetooth.menu",
FALSE

Any idea why it is not detecting that they are the same?

I suspect that Output contains leading spaces, that can't be seen by OP with unquoted (horror!) echo $Output, so OP is very confused. OP should learn how to properly use quotes. But I'm just assuming. OP should learn how to properly use quotes anyway. — gniourf_gniourf
– gniourf_gniourf, Commented Feb 12, 2015 at 19:32

Gordon Davisson · Accepted Answer · 2015-02-12 20:20:45Z

1

As everyone in the comments suspected, the problem is whitespace in $Output (which echo $Output removes); specifically, 4 leading spaces (note that in the following, "$ " is my shell prompt):

$ defaults read com.apple.systemuiserver menuExtras | grep Bluetooth.menu
    "/System/Library/CoreServices/Menu Extras/Bluetooth.menu",
$ Output=$(defaults read com.apple.systemuiserver menuExtras | grep Bluetooth.menu)
$ echo $Output
"/System/Library/CoreServices/Menu Extras/Bluetooth.menu",
$ echo "[$Output]"
[    "/System/Library/CoreServices/Menu Extras/Bluetooth.menu",]
$ Check="    \"/System/Library/CoreServices/Menu Extras/Bluetooth.menu\","
$ if [ "$Output" = "$Check" ]; then echo "OK"; else echo "FALSE"; fi
OK

Note that since the number of spaces might not always be the same, it might be safer to use bash's wildcard matching capability within a [[ ]] conditional expression (this will not work with [ ]):

$ Check="\"/System/Library/CoreServices/Menu Extras/Bluetooth.menu\","
$ if [[ "$Output" = *"$Check" ]]; then echo "OK"; else echo "FALSE"; fi
OK

You could also skip the string comparison entirely, and just use the fact that grep returns a success status only if it finds a match:

#!/bin/bash
if defaults read com.apple.systemuiserver menuExtras | grep -q "/System/Library/CoreServices/Menu Extras/Bluetooth.menu"; then
    echo "OK"
else
    echo "FALSE" 
    echo "Security Compliance Setting 'Show Bluetooth Status in Menu Bar(2.1.3)' has been changed!" | logger
fi

edited Feb 12, 2015 at 20:20

answered Feb 12, 2015 at 20:06

Gordon Davisson

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1 Comment

Technic1an Over a year ago

Thank you for you amazing answer Gordon! It is much appreciated!

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