Null & empty string comparison in Bash [duplicate]

Question

I don't set any values for $pass_tc11; so it is returning null while echoing. How to compare it in if clause?

Here is my code. I don't want "Hi" to be printed...

-bash-3.00$ echo $pass_tc11  -bash-3.00$ if [ "pass_tc11" != "" ]; then > echo "hi" > fi hi -bash-3.00$ 

Answer 1

First of all, note you are not using the variable correctly:

if [ "pass_tc11" != "" ]; then #     ^ #     missing $ 

Anyway, to check if a variable is empty or not you can use -z --> the string is empty:

if [ ! -z "$pass_tc11" ]; then    echo "hi, I am not empty" fi 

or -n --> the length is non-zero:

if [ -n "$pass_tc11" ]; then    echo "hi, I am not empty" fi 

From man test:

-z STRING

the length of STRING is zero

-n STRING

the length of STRING is nonzero

Samples:

$ [ ! -z "$var" ] && echo "yes" $  $ var="" $ [ ! -z "$var" ] && echo "yes" $  $ var="a" $ [ ! -z "$var" ] && echo "yes" yes  $ var="a" $ [ -n "$var" ] && echo "yes" yes