Logical expressions in bash

logical_expressions.csv

Logical expression, Meaning
String comparion, 
if [ -n "$variable" ], Returns true if the variable is empty/null
if [ -z "$variable" ], Returns true if the variable is not empty/null
if [ "$variable1" = "$variable2" ], Returns true if variable 1 is equal to variable 2
if [ "$variable1" == "$variable2" ], Returns true if variable 1 is equal to variable 2
if [ "$variable1" != "$variable2" ], Returns true if variable 1 is not equal to variable 2
if [ "$variable1" \< "$variable2" ], Returns true if variable 1 is less than variable 2 in ASCII. The < is escaped (\<)
if [ "$variable1" \> "$variable2" ], Returns true if variable 1 is greater than variable 2 in ASCII.
Integer comparison, 
if [ $variable -eq 0 ], Returns true if the variable is the equal to  zero
if [ $variable -ne 0 ], Returns true if the variable is not equal to zero
if [ $variable -gt 0 ], Returns true if the variable is greater than zero
if [ $variable -lt 0 ], Returns true if the variable is less than zero
if [ $variable -ge 0 ], Returns true if the variable is greater than or equal to zero
if [ $variable -le 0 ], Returns true if the variable is less than or equal to zero
Files and directories, 
if [ -f "$variable" ], Returns true if the variable is the name of a file
if [ ! -f "$variable" ], Returns true if the variable is not the name of a file
if [ -d "$variable" ], Returns true if the variable is a directory
Combining conditions, 
if [ "$variable1" = "true" -o "$variable1" = "false" ], Returns true if variable 1 is equal to true or false
if [ $variable1 -gt 3 -a $variable1 -lt 1 ], Returns true if variable 1 is greater than 3 and less than 1