Bash if else string variable comparison

Question

I am writing a shell script at which I am trying to compare 2 variables that are strings. Every thing works fine as in all the variables have a value from the commands however my if then else statement is not working.

#!/bin/bash

name=$1

for i in {1...10} 

do        
username=sudo cat /class/rolls/CSCE215-*|awk 'BEGIN {FIELDWIDTHS = "32 20"} {print $2}'|cut -d " " -f6 |sed -n '1,1p'

if ["$name" == "$username"] 
then  
echo Correct Username
else
echo Incorrect Username
fi  

done

All of the tutorials and help online appears to have what I have here but I cannot find out what is wrong with mine.

You should add spaces after [ and before ]: if [ "$name" == "$username" ] — user142162
– user142162, Commented Sep 16, 2014 at 22:16

rje · Accepted Answer · 2014-09-16 22:21:00Z

2

You are using the "classic test" but it's a good idea to ALWAYS use the newer conditional expression: http://wiki.bash-hackers.org/syntax/ccmd/conditional_expression

if [[ "$name" == "$username" ]]

As far as I know the test command (with a single bracket) doesn't even officially support the "==" operator..

Oh, and of course don't forget the spaces inside the brackets, bash needs them to break the line up into words.

answered Sep 16, 2014 at 22:21

rje

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Comments

David C. Rankin · Accepted Answer · 2014-09-16 22:39:21Z

1

When using test or [, the correct comparison is:

test "$string1" = "string2"

or

[ "$sting1" = "$string2" ]

Note: the single = instead of ==, and always quote sting variables. Further, there is nothing wrong with using the test or [ operators, in fact, they are preferred when portability is needed. They simply lack some of the extended functionality of the [[ operator, such as character class comparison and the ability to use =~.

Now when using the [[ operator, the correct form is:

[[ "$sting1" == "$string2" ]]

Note: as pointed out, quotes are not required when using the [[ operator, but if you get in the habit of always quoting strings, you will be safe in both cases.

edited Sep 16, 2014 at 22:39

answered Sep 16, 2014 at 22:33

David C. Rankin

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5 Comments

jaypal singh Over a year ago

+1: s/sting/string and quotes are not required inside [[ .. ]].

David C. Rankin Over a year ago

Correct, but as a general rule, I prefer to explain it with quoted variables for the benefit of those that lack that depth of understanding on whether quotes are required with [ or [[. That way they default to a safe expression.

rje Over a year ago

You are right that test is preferred for portability. It does have a lot of nasty pitfalls. In many cases portability is not an issue (most of the time you're pretty sure you're always going to run the script with bash) and so I'd say the conditional expression is actually preferred.

rje Over a year ago

Just another thing: the conditional expression does not just extend functionality. It is a part of bash syntax - the test operator [ is not - it is a regular command. Word splitting and pathname expansion are not done on a conditional expression and that is why - in my opinion at least - it should be preferred over the test command whenever portability is not necessary.

Reinstate Monica Please Over a year ago

@DavidC.Rankin = and == are synonymous in bash. = is only preferred if you want portability.

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