Bash script error, integer expression expected

Question

I'm getting an error saying

"line 6: [: : integer expression expected"

and I can't figure out what to do to fix it. I'm trying to write a script to print out 200 equations, the equations should be of form "i * j = k" where i is an integer between 1 and 10, j is between 1 and 20, k is the product of i and j.

#!/bin/bash

for i in {1..200..1}
do

    if [ "$i" -gt 0 ]  && [ "$i" -lt 11 ] && [ "$j" -gt 0 ] && [ "$j" -lt 21 ]
        then 
        i = 1
        j = 1
        k = $(($i * $j))
           echo $i * $j = $k
           ((i++))
           ((j++))
    fi
done

Maybe because $j is undefined on the first pass through the loop? — Jim Lewis
– Jim Lewis, Commented Feb 18, 2016 at 23:31
What Jim says, then you can't have spaces in variable assignments, you must quote the argument of echo or it tries to expand *, and you'll end up with 1 * 1 = 1 for every loop because you set i and j to 1 before the calculation. shellcheck.net would have uncovered at least the spaces. — Benjamin W.
– Benjamin W., Commented Feb 18, 2016 at 23:46

assefamaru · Accepted Answer · 2016-02-19 01:17:04Z

In your script, both i and j get initialized to 1, which means your entire loop echoes 1 * 1 = 1, 200 times. Furthermore, j is not defined the first time your if statement tests $j, hence you got the error message "line 6: [: : integer expression expected".

One way of printing 200 equations, with combinations of i and j, where i is an int between 1 and 10, and j is between 1 and 20, is as follows:

#!/bin/bash

for (( i = 1; i <= 10; i++ )); do
    for (( j = 1; j <= 20; j++ )); do
        k=$(( i * j ))      # Note no space before/after equal sign
        echo "$i * $j = $k" # Note the quotation mark
    done
done

Or you can do the same thing in a different format as follows:

#!/bin/bash

for i in {1..10}; do
    for j in {1..20}; do
        k=$(( i * j ))
        echo "$i * $j = $k"
    done
done

This way, both i and j get initialized before any statements are executed, and you can set the max and min restrictions on both within the loops.

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