Bash conditional expression: `-o`. What does it mean?

Question

I am trying to understand what dose the -o mean in the following bash if script.

looking at the results I can guess what it does but I do really need to get the concept of it.

i=1 for day in Mon Tue Wed Thu Fri Sat Sun do echo -n "Day $((i++)) : $day" if [ $i -eq 7 -o $i -eq 8 ]; then echo " (WEEKEND)" continue; fi echo " (weekday)" done

The results are as following:

$ ./for7.sh Day 1 : Mon (weekday) Day 2 : Tue (weekday) Day 3 : Wed (weekday) Day 4 : Thu (weekday) Day 5 : Fri (weekday) Day 6 : Sat (WEEKEND) Day 7 : Sun (WEEKEND)

As it is used there, it means || (OR). e.g. $i -eq 7 OR $i -eq 8. It can also be used to test whether an option set by set is set... (that's a lot of sets). That is why you are better off using [ "$i" -eq 7 ] || [ "$i" -eq 8 ] (note: always quote your variables with [...]) — David C. Rankin
– David C. Rankin, Commented Nov 7, 2017 at 4:05
If you use bash then [ is a builtin command. See: help test. — Cyrus
– Cyrus, Commented Nov 7, 2017 at 4:47

sjsam · Accepted Answer · 2017-11-07 04:13:07Z

The -o symbolizes Logical OR here.

Do man test which explains this.

 EXPRESSION1 -o EXPRESSION2 either EXPRESSION1 or EXPRESSION2 is true

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