Bash multiple string comparison with OR and NOT

Question

Pulling disk status from a disk array, I get "ready" and "online" as status for OK. Trying to trap this with an IF statement in bash, that will act if the value is something else than "ready" and "online".

The code snippet below works for trapping "OK" but I'd like to reverse it, so it traps if $diskstatus is NOT ready or online.

#!/bin/bash
diskstatus="online"
if [[ $diskstatus = online ]] || [[ $diskstatus = ready ]]; then echo "OK: $diskstatus"; fi

Have now tried nearly everything with brackets, quotes and whatnot but not getting any of it to work.

tripleee · Accepted Answer · 2017-02-20 08:50:34Z

3

Just for completeness, consider also the case statement.

case $diskstatus in
    online | ready) ;;
    *) echo "Not ok: $diskstatus";;
esac

The syntax may look arcane at first but you quickly get used to it. I actually tend to prefer it over if for many things involving simple string pattern matching. As a bonus, it's compatible with traditional sh.

answered Feb 20, 2017 at 8:50

tripleee

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1 Comment

tompaah Over a year ago

Thanks, didn't think about that. I use case a lot in command input parameter parsing.

Community · Accepted Answer · 2017-05-23 12:00:07Z

2

Use the regex operator in bash with [[ operator as below,

[[ ! $diskstatus =~ ^(ready|online)$ ]] && echo "Not OK: $diskstatus"

Also, observe that double-quotes are not needed either for the regex or for the variable part, because neither word-splitting nor pathname expansion(globbing) will be performed in this context

Another POSIX way to do this, to add to tripleee's answer would be as

if [ "$diskstatus" != "ready" ] && [ "$diskstatus" != "online" ]; then  echo "Not OK: $diskstatus"; fi

edited May 23, 2017 at 12:00

CommunityBot

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answered Feb 20, 2017 at 8:37

Inian

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2 Comments

George Vasiliou Over a year ago

I had this solution in my mind, but I was squeezing my head how to make it work. Nice job.

tompaah Over a year ago

Thanks for the regex variety, for the sake of readability it is very elegant. I'll pick this one :)

Guest · Accepted Answer · 2017-02-20 08:39:42Z

0

Since both need to be false, you have to use an and statement.

if [[ $diskstatus != online ]] && [[ $diskstatus != ready ]]; then echo "OK: $diskstatus"; fi

Otherwise, since at least one of the conditions will always be true, your if statement's body will always run.

answered Feb 20, 2017 at 8:39

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VirgileD · Accepted Answer · 2017-02-20 08:54:03Z

0

simply reversing equality and logical operator seems to work for me

$ diskstatus=onlin
$ if [[ $diskstatus != online ]] && [[ $diskstatus != ready ]]; then echo "NOK: $diskstatus"; fi
NOK: onlin

edited Feb 20, 2017 at 8:54

answered Feb 20, 2017 at 8:39

VirgileD

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2 Comments

tripleee Over a year ago

There is no reason to export the variable here.

VirgileD Over a year ago

@tripleee you're right, I removed the useless but harmless export

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