Unix Bash - Assign if/else to Variable

Question

I have been creating to assign the output of if/else to a variable but keep on getting an error.

For Example:

mathstester=$(If [ 2 = 2 ]
Then echo equal
Else
echo "not equal"

fi)

So whenever I add $mathstester in a script, laid out like this:

echo "Equation: $mathstester"

It should display:

Equation: Equal

Do I need to lay it out differently? Is it even possible?

what are you trying to do? your if statement is missing a fi. — Jason Hu
– Jason Hu, Commented Mar 21, 2015 at 14:48
That's not the correct syntax for an if. This will work: x = $(if [ 2 = 2 ]; then echo equal; else echo "not equal; fi). See gnu.org/software/bash/manual/bash.html#Conditional-Constructs . Note that case matters -- If and if are not the same. — Ulfalizer
– Ulfalizer, Commented Mar 21, 2015 at 14:50
if you want to echo it in one line. you need echo -n text. — Jason Hu
– Jason Hu, Commented Mar 21, 2015 at 14:50

RomanPerekhrest · Accepted Answer · 2017-10-19 10:42:35Z

15

The correct way to use if is:

mathtester=$(if [ 2 = 2 ]; then echo "equal"; else echo "not equal"; fi)

For using this in multiline statements you might consider looking link.

edited Oct 19, 2017 at 10:42

RomanPerekhrest

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answered Mar 21, 2015 at 14:58

baky

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2 Comments

space149 Over a year ago

How about if I have a variable called $number which a 5, how would put that into the if statement?

baky Over a year ago

How about reading the bash basics ? tldp.org/LDP/Bash-Beginners-Guide/html

Gordon Davisson · Accepted Answer · 2015-03-21 20:30:31Z

Putting the if statement in the assignment is rather clumsy and easy to get wrong. The more standard way to do this is to put the assignment inside the if:

if [ 2 = 2 ]; then
    mathstester="equal"
else
    mathstester="not equal"
fi

As for testing variables, you can use something like if [ "$b" = 2 ] (which'll do a string comparison, so for example if b is "02" it will NOT be equal to "2") or if [ "$b" -eq 2 ], which does numeric comparison (integers only). If you're actually using bash (not just a generic POSIX shell), you can also use if [[ "$b" -eq 2 ]] (similar to [ ], but with somewhat cleaner syntax for more complicated expressions), and (( b == 2 )) (these do numeric expressions only, and have very different syntax). See BashFAQ #31: What is the difference between test, [ and [[ ? for more details.

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