Null & empty string comparison in Bash
123684
Test for non-zero length string in Bash: [ -n "$var" ] or [ "$var" ]
89933
How do I avoid trailing empty items being removed when splitting strings?
49243
How to trim whitespace from a Bash variable?
123797
Not equal  != operator on NULL
153835
Bash scripting: test for empty directory
5374
How to check if a macro value is empty or will not create text with plain TeX conditionals?
5377
Is there a standard function to check for null, undefined, or blank variables in JavaScript?
109443
Compare integer in bash, unary operator expected
40539
How do I use regular expressions in bash scripts?
136671
Shell script comparison does not work as intended
35796
Difference between 2>&-, 2>/dev/null, |&, &>/dev/null and >/dev/null 2>&1
110007
What is the difference between operator "=" and "==" in Bash?
27495
Why is True returned when checking if an empty string is in another?
104501
How do I enforce null checking?
15435
how to check if $1 and $2 are null?
113229
How do I compare two strings in Perl?
109812
Issue an error when using empty shell variables