mjhjmtu

I faced some issue, where OR operator doesn't work for $1.
Eg:

if [[ "$1" != '1' || '2' ]]
 then
 echo "BAD"
 else
 echo "OK"
 fi

When I run this test no matter what $1 is, BAD always appears.

How can I tie $1 to be 1 or 2 only?

With standard sh syntax (so not only recognised by bash but all other POSIX compatible shells):

case $1 in
 (1 | 2) echo OK;;
 (*) echo BAD;;
esac

Or:

if [ "$1" = 1 ] || [ "$1" = 2 ]; then
 echo OK
else
 echo BAD
fi

(note that it's a byte-to-byte comparison of strings. 01, 1e0, 1.0, 20/20, 0x1 would also be considered as BAD even though numerically they could be regarded as being the same as 1).

Note that the =/!= operators in bash's [[...]] construct (copied from ksh) are actually pattern matching operators as opposed to equality operators, so in this special case where you want to match a single character, you could also use [[ $1 != [12] ]] like you could do case $1 in ([12]) in standard sh syntax.

The reason you always go into the BAD branch of the if statement is that the test

[[ "$1" != '1' || '2' ]]

first tests whether $1 is not 1, and if it is not, BAD is printed. If it is, 2 is evaluated as a test. A string like 2 is always true, and BAD is printed.

Instead:

if [ "$1" != '1' ] && [ "$1" != '2' ]; then

or, with arithmetic tests,

if [ "$1" -ne 1 ] && [ "$1" -ne 2 ]; then

or, using arithmetic evaluation,

if (( $1 != 1 )) && (( $1 != 2 )); then

if [[ "$1" != '1' || "$1" != '2' ]]
then
 echo "BAD"
else
 echo "OK"
fi

Then != statement needs to be repeated for the not equal to 2 as well as 1

The logic of ($1 != 1) OR ($1 != 2) is flawed.

If $1 is 1 then it is not equal to 2 so the test will be true.

Also, if $1 is 2 then it is not equal to 1 so the test will be also true.
In short, the test will always be true.

You should test equality: ($1 == 1) or ($1 == 2) like this:

if [[ ($1 == '1') || ($1 == '2') ]]; then
 echo "$1 OK"
else
 echo "$1 BAD"
fi

Or simpler (in ksh, bash or zsh):

[[ $1 == [12] ]] && echo "$1 OK" || echo "$1 BAD"

Or using sh syntax (portable to all POSIX shells):

if [ "$1" = '1' ] || [ "$1" = '2' ]; then
 echo "$1 OK"
else
 echo "$1 BAD"
fi

Or with a case idiom:

case $1 in
 (1 | 2) echo "$1 OK" ;;
 (*) echo BAD "$1 BAD" ;;
esac

All the above is a string comparison, if you want a numeric comparison, you may do:

if [ "$1" -eq 1 ] || [ "$1" -eq 2 ]; then
 echo "$1 OK"
else
 echo "$1 BAD"
fi

However, that will not work if $1 is 1.0 or 1e0 or many other numerical equivalent to 1. Will work with 01 or 0001 though.