I read in tldp.com that
if [ $condition1 ] && [ $condition2 ]
Same as: if [ $condition1 -a $condition2 ]
Returns true if both condition1 and condition2 hold true..."
but when I tried
if [ $a == 2 ] || [ $b == 4 ] then echo "a or b is correct" else echo "a and b are not correct" fi
it gives error. I'm using bash.
Your logic is ok but your comparison operators are incorrect, you should use the '-eq' for comparing integers and '==' for strings. See 'man test' for quick reference, though it's also documented in 'man bash'.
When using integer comparison it is always best to initialise variables to 0 as well otherwise if they remain unset you will get errors.
As mentioned by c00k, use [[ rather than [ if using bash as it is a builtin so bash will not need to shell out to use the /usr/bin/[ command.
a=0;b=0 # do something else with a or b if [[ $a -eq 2 ]] || [[ $b -eq 4 ]] then echo "a or b is correct" else echo "a and b are not correct" fi