"or" in bash scripting

Question

Script has to check if OLD_VERSION is not empty or if it doesn't match some pattern. I tried the below code

#!/bin/bash
OLD_VERSION="ABCDEFGHIJKL"
PATTERN="ABC"
if [[ ! "$OLD_VERSION" =~ "$PATTERN" ]] || [[ ! -z "$OLD_VERSION" ]];
then
    echo "Not matched or not null"
else
    echo "matched or null"
fi

For the above inputs :

 bash -x re.sh
 + OLD_VERSION=ABCDEFGHIJKL
 + PATTERN=ABC
 + [[ ! -z ABCDEFGHIJKL ]]
 + echo 'Not null or doesnot match'

I get the below output:

Not null or doesnot match

and also when I make old_version null, i get Not null or doesnot match, where i expect it to print null.

$OLD_VERSION=""

+ PATTERN=ABC
+ OLD_VERSION=
+ [[ ! -z '' ]]
+ [[ ! '' =~ ABC ]]
+ echo 'Not null or doesnot match'

I get wrong output. I am getting problem in or. What am I doing wrong?

UPDATE :

as suggested by sureshvv , i updated it like :

if [[ ! "$OLD_VERSION" =~ "$PATTERN"  && ! -z "${OLD_VERSION}" ]] ;
then
    echo "Not null or doesnot match"
else
    echo "matched or null"
fi

Thanks all.

May be easier to read if you get rid of the double negative. So you can say if [ -z "$OLD_VERSION" || "$OLD_VERSION" =~ "$PATTERN" ]; then echo null or matched; fi — sureshvv
– sureshvv, Commented Oct 19, 2015 at 9:06

sureshvv · Accepted Answer · 2015-10-19 08:00:04Z

3

I think you want:

if [[ ! -z "$OLD_VERSION" && "$OLD_VERSION" =~ "$PATTERN" ]]; then
    echo Matched
else
    echo No match
fi

answered Oct 19, 2015 at 8:00

sureshvv

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3 Comments

no1 Over a year ago

thanks. But i got "matched" when i make old_version null

no1 Over a year ago

I got desired output when i changed it like " if [[ ! -z "$OLD_VERSION" && ! "$OLD_VERSION" =~ "$PATTERN" ]]; then "

amdixon Over a year ago

check if you inverted the order ( answer is opposite echo order to yours )

Zang MingJie · Accepted Answer · 2015-10-19 07:55:41Z

-1

|| is handled by command [[, so you must put it inside [[ and ]]

if [[ ! "$OLD_VERSION" =~ "$PATTERN" || ! -z "$OLD_VERSION" ]];

answered Oct 19, 2015 at 7:55

Zang MingJie

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1 Comment

Ignacio Vazquez-Abrams Over a year ago

Or it could be used as the bash command failure chain operator.

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