Store bash string comparison in variable

Question

I want to store the result of a bash string comparison in a variable, with effect equivalent to:

if [[ $a == $b ]]; then
    res=1
else
    res=0
fi

I was hoping to be able to write something terser, like:

res2=$('$a'=='$b') #Not valid bash

Is there a way to achieve what I want, without deferring to an if construct?

twalberg · Accepted Answer · 2012-11-09 16:45:32Z

27

I would suggest either:

res=0; [ "$a" == "$b" ] && res=1

or

res=1; [ "$a" == "$b" ] || res=0

Not quite as simple as you were hoping for, but does avoid the if ... else ... fi.

answered Nov 9, 2012 at 16:45

twalberg

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1 Comment

cmh Over a year ago

Thanks for the suggestion. I think in this form I would prefer to go with [ "$a" == "$b" ] && res=1 || res=0 as it has the more familiar c-style ternary structure.

Tim Pote · Accepted Answer · 2012-11-09 16:55:27Z

5

You could also use the $? variable which contains the return value from the previous command:

res="$( [[ $a == $b ]]; echo $? )"

Although that would inverse the numbers you gave. The end result would be the same as:

if [[ $a == $b ]]; then
  res=0
else
  res=1
fi

That's because the shell interprets a return value of 0 as true and 1 as false.

Not saying I wholly advocate this solution either. It's hackish and a bit unclear. But it is terse and terse is what you asked for.

answered Nov 9, 2012 at 16:55

Tim Pote

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Comments

def- · Accepted Answer · 2023-10-19 07:52:20Z

3

res2=$(expr "$a" == "$b")

answered Oct 19, 2023 at 7:52

def-

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Comments

plafratt · Accepted Answer · 2019-07-25 15:09:33Z

1

Here is another option.

$> test "foo" = "bar"; res=$?
$> echo $res
1
$> test "foo" = "foo"; res=$?
$> echo $res
0

answered Jul 25, 2019 at 15:09

plafratt

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