Comparing an integer variable in the Bash shell [duplicate]

Question

I know I'm missing something very obvious, but I just can't see it. In the code below, new_i variable gets incremented properly, however, when I get to the if statement, I think my syntax is off. I looked at some examples, but none show variable set to zero when if statement is greater than (in this case 15) a number.

#!/bin/sh
i=$(cat /etc/hour.conf)
new_i=$((i+1))
if [[ "$new_i" -gt 15 ]]; then
 new_i=0
fi
echo "$new_i">/etc/hour.conf
echo "$new_i"

When I run this script I get the following error:

./loops: 3: ./loops: Illegal number: new_i

Thanks in advance for your help!

Ah, the problem is on line 3... What is content of /etc/hour.conf? — grundic
– grundic, Commented Jun 16, 2017 at 14:27
Hm.. Can you cat that file? echo 0>x.txt && cat x.txt gives me empty file. To fix it you have to add space before >: echo 0 >/etc/hour.conf — grundic
– grundic, Commented Jun 16, 2017 at 14:30

user3308131 · Accepted Answer · 2017-06-16 14:50:19Z

2

This works - the $ in front of the i in the new_i=$(( line and the removal of the quotes and one set of the brackets fixed the errors and now the scripts works as intended. Thanks to everyone for their help!

#!/bin/sh
i=$(cat /etc/hour.conf)
new_i=$(($i+1))
if [ $new_i -gt 15 ]; then
 new_i=0
fi
echo "$new_i">/etc/hour.conf
echo "$new_i"

answered Jun 16, 2017 at 14:50

user3308131

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4 Comments

zhenguoli Over a year ago

$((i+1)) works the same as $(($i+1)) if i is a valid number. And the code you posted works if I change the filename to x.txt and set it initial content to empty.