Assigning the output of a C program in unix shell script and checking the value

Question

Let's say I have a C program that evaluates to either a zero or non zero integer; basically a program that evaluates to a boolean value.

I wish to write a shell script that can find out whether the C program evaluates to zero or not. I am currently trying to assign the return value of the C program to a variable in a shell script but seem to be unable to do so. I currently have;

#!/bin/sh
variable=/path/to/executable input1

I know that assigning values in shell script requires us not to have spaces, but I do not know another way around this, since running this seems to evaluate to an error since the shell interprets input1 as a command, not an input. Is there a way I can do this?

I am also unsure as to how to check the return value of the C program. Should I just use an if statement and check if the C program evaluates to a value equal to zero or not?

BTW: the fact that the program is a c program doesn't mean that you need to tag the question as a c question. — Iharob Al Asimi
– Iharob Al Asimi, Commented Feb 5, 2016 at 15:47
Aah, I apologize. I don't go here often. Your advice is noted however. — TheValars
– TheValars, Commented Feb 5, 2016 at 15:51

Iharob Al Asimi · Accepted Answer · 2016-02-05 15:47:05Z

4

This is very basic

#!/bin/sh
variable=`/path/to/executable input1`

or

#!/bin/sh
variable=$(/path/to/executable input1)

and to get the return code from the program use

echo $?

answered Feb 5, 2016 at 15:47

Iharob Al Asimi

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1 Comment

TheValars Over a year ago

Ah, it is that simple. Apologies for my noob-ness. Thank you though.

Community · Accepted Answer · 2017-05-23 12:31:18Z

1

You can assign with backticks or $(...) as shown in iharob's answer.

Another way is to interpret a zero return value as success and evaluate that directly (see manual):

if /path/to/executable input1; then
    echo "The return value was 0"
else
    echo "The return value was not 0"
fi

Testing with a little dummy program that exits with 0 if fed "yes" and exits with 1 else:

#!/bin/bash

var="$1"

if [[ $var == yes ]]; then
    exit 0
else
    exit 1
fi

Testing:

$ if ./executable yes; then echo "Returns 0"; else echo "Doesn't return 0"; fi
Returns 0
$ if ./executable no; then echo "Returns 0"; else echo "Doesn't return 0"; fi
Doesn't return 0

_{If not using Bash: if [ "$var" = "yes" ]; then}

edited May 23, 2017 at 12:31

CommunityBot

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answered Feb 5, 2016 at 16:15

Benjamin W.

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