#!/bin/sh

• bash
• csh
• ksh
• tcsh
• zsh

• Bourne shell programming
• Summary of shell facilities
• Capturing signal traps

sh uses different syntax for operators than bash.

Use -o for or in place of || and -a for and in place of &&.

• $1..$9 - arguments
• $0 - process name
• $# - number of arguments
• $? - exit status
• $$ - PID of this shell
• $! - PID of the last background command
• $- - option supplied at shell call (?)
• $* - all arguments
• $@ - all arguments with quotes

• -a and (has higher precedence than -o)
• -o or

• = or == equal to
• -n string is not null
• -z string is null, that is, has zero length

• -eq number equals
• -ne number does not equal
• -gt greater than
• -ge greater than or equal to
• -lt less than
• -le less than or equal to

• -e file exists
• -f file is not a directory or device file
• -d file exists and is a directory
• -h file exists and is a symlink
• -s file exists and has a size greater than zero
• -w file exists and is writeable
• -x file exists and is executable
• -r file exists and is readable
• -b file is a block device
• -c file is a character device
• -p file is a pipe
• -S file is a socket
• -O you are owner of file
• -G you are group owner of file

• : - null command
• . file - execute command in current shell
• read - assign var from stdin
• readonly - mark var as read only
• trap - trap signals
• type - inidicate how the shell interprets the command
• exec - execute command in place of current shell without creating a new process
• hash - rehash command table

echo test 2> /dev/null

echo test 2>&1

When checking for string length, include the string in quotes.

Both of these will return true:

[ -n string ]
[ -n ]

This will return false:

[ -n "" ]