reference: https://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php
if [ <some test> ]
then
<commands>
fi
================== compare number ================
#!/bin/bash
# Basic if statement
if [ $1 -gt 100 ]
then
echo Hey that\'s a large number.
pwd
fi
================== compare string ================
#!/bin/sh
if [ -z $1 ]
then
echo "no input string given"
return
fi
==============================================
| Operator | Description |
|---|---|
| ! EXPRESSION | The EXPRESSION is false. |
| -n STRING | The length of STRING is greater than zero. |
| -z STRING | The lengh of STRING is zero (ie it is empty). |
| STRING1 = STRING2 | STRING1 is equal to STRING2 |
| STRING1 != STRING2 | STRING1 is not equal to STRING2 |
| INTEGER1 -eq INTEGER2 | INTEGER1 is numerically equal to INTEGER2 |
| INTEGER1 -gt INTEGER2 | INTEGER1 is numerically greater than INTEGER2 |
| INTEGER1 -lt INTEGER2 | INTEGER1 is numerically less than INTEGER2 |
| -d FILE | FILE exists and is a directory. |
| -e FILE | FILE exists. |
| -r FILE | FILE exists and the read permission is granted. |
| -s FILE | FILE exists and it's size is greater than zero (ie. it is not empty). |
| -w FILE | FILE exists and the write permission is granted. |
| -x FILE | FILE exists and the execute permission is granted. |
