bash

-d check if the file is a directory
-e check if the file exists
-f check if the file is a regular file
-g check if the file has SGID permissions
-r check if the file is readable
-s check if the file's size is not 0
-u check if the file has SUID permissions
-w check if the file is writeable
-x check if the file is executable

Checks equality between numbers:
x -eq y Check is x is equals to y
x -ne y Check if x is not equals to y
x -gt y Check ifx is greater than y
x -lt y Check if x is less than y

Checks equality between strings:
x = y Check if x is the same as y
x != y Check if x is not the same as y
-n x Evaluates to true if x is not null
-z x Evaluates to true if x is null

Trapping CTRL-C in a Bash Script

#!/bin/bash
# trap ctrl-c and call ctrl_c()
trap ctrl_c INT
function ctrl_c() {
        echo "** Trapped CTRL-C!"
}
for i in `seq 1 5`; do
    sleep 1
    echo -n "."
done