Question

I have a simple bash script.

# Which display is HDMI ?
for i in `seq 0 $displayLoopCounter`
do
    name=$(adb shell cat /sys/devices/platform/omapdss/display$i/name)

    if [ "$name"=="hdmi" ] ; then
        echo "$name"
        hdmiDisplay="display$i"
    fi
done

OUTPUT of my scipt:

dvi

hdmi

I’m running the scripts using bash myscript.sh

display0 is dvi

display1 is hdmi

Answer 1

Your problem lies with the fact that you don’t have spaces around the == in your if line. That makes it a single-argument expression about which the bash manpage states:

1 argument: The expression is true if and only if the argument is not null.

If you run the following script (with no spaces around the ==):

#!/bin/bash
echo Hello >myfile0
echo fileData >myfile1
counter=1
for i in `seq 0 $counter`
do
    name=$(cat myfile$i)
    if [ "$name"=="fileData" ]; then
        echo $name
    fi
done
rm myfile[01]

you’ll see that the output has both lines, Hello and fileData. Putting the spaces in, you’ll get only fileData because that same manpage states:

3 arguments: If the second argument is one of the binary conditional operators listed above under CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary test using the first and third arguments as operands.