How to test multiple variables for empty string

Question

I want to test multiple variables to see if they are empty. So I did the following:

if [ test -z "$VAR1" ] || [ test -z "$VAR2" ]
then
   echo "Empty!"
fi

However, it doesn't work. The output is:

[: -z: binary operator expected
[: -z: binary operator expected

What have I done wrong? The code above works fine if I leave out the OR (||) condition.

if [[ -z "$VAR1" || -z "$VAR2" ]]; then ... fi should work in bash — anubhava
– anubhava, Commented Sep 17, 2019 at 15:03
[ is test, not part of the if statement's syntax. Type help [ and help test at the prompt for more information. — chepner
– chepner, Commented Sep 17, 2019 at 15:14

Graeme · Accepted Answer · 2019-09-17 15:22:47Z

5

Use either brackets or the test command, don't use both. Either of the following will work:

if [ -z "$VAR1" ] || [ -z "$VAR2" ]
then
   echo "Empty!"
fi

Or:

if test -z "$VAR1" || test -z "$VAR2"
then
   echo "Empty!"
fi

In some older shells [ was just an alias for the test command. You could even miss out the closing ] (or add it after test) and everything would be fine. Nowadays, on bash this will give a syntax error. However, the two (correct) syntaxes are still functionally equivalent and can be used interchangeably but not at the same time.

edited Sep 17, 2019 at 15:22

answered Sep 17, 2019 at 15:04

Graeme

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Comments

oguz ismail · Accepted Answer · 2019-09-18 08:05:16Z

2

You should either use test, or [; they are synonymous, except [ requires a ] as last argument.

[ -z "$VAR1" ] || [ -z "$VAR2" ]

or

test -z "$VAR1" || test -z "$VAR2"

edited Sep 18, 2019 at 8:05

answered Sep 17, 2019 at 15:03

oguz ismail

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