How to do string equality with AND operator in shell script

Question

if [ $string1 = $string2 -a $string3 = $string4 ]; then 

results [: too many arguments. How to resolve this error?

Answer 1

With the single bracket test, [ .. ], you should use quotes around the variable names in the test brackets. Otherwise Bash will break the string on any spaces.

With:

$ s1="one two"
$ s2="one two"

If you do not quote your variable:

$ [ $s1 = $s2 ]; echo $?
-bash: [: too many arguments

But if you quote -- all is good:

$ [ "$s1" = "$s2" ]; echo $?
0

(0 means True in this case)

You can also use the Bash [[ ... ]] two bracket test and not use "quotes" SOMTIMES:

$ [[ $s1 == $s2 ]]; echo $?
0

For the 'and' part, you can use && either inside or outside the [[ ... ]] square braces:

$ s3="three"
$ s4="four"
$ [[ $s1 == $s2 ]] && [[ $s3 == $s4 ]]; echo $?
1
$ [[ $s1 == $s2 && $s3 == $s4 ]]; echo $?
1

But really -- it is best to quote all the time.

See this SO post.

Answer 2

Or if strictly Bash/Ksh

#!/bin/bash

s1="one two"
s2="one two"
s3="three four"
s4="three four"


if [[ $s1 == $s2 && $s3 == $s4 ]]; then
        echo "All equals"
else
        echo "Some differences"
fi

Within [[ ]] there would be no word splitting normally and thus no need for quoting. Also, "&&" is generally preferred instead of "-a" for AND nowadays.

Hope it helps.