options that can be used in if condition check

Question

if [ -z "$1" -o -z "$2" ] - Here i know that -z option is used to check for zero length string but why we are using -o option along with -z.

And also tell me any suitable link to study about those options

Thanks in advance,

Answer 1

-o simply stands for OR. The expression is true if one of the strings had a zero length. Have a look at table 7.2 on http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

Answer 2

The "[" is an alias to the test bash builtin.

$ test 1 -gt 2
$ echo $?
1

is equivalent to

$ [ 1 -gt 2 ]
$ echo $?
1

You can see the relative man page for further options.

man test

or this article for example