Shell options reference

shell-options.sh

# Expressions
-a # file exists
-f # file exists and is a regular file
-h # file exists and is a symbolic link
-r # file exists and is readable
-w # ... and is writable
-x # ... and is executable
-S # ... and is a socket

# Special Vars
$1 - $9 # positional arguments 
$0      # command name e.g. "./test.sh cmd" where `cmd` is command
$#      # number of arguments
$?      # exit status of last command 
$$      # process number of this shell
$!      # process id of last command run in the background
$-      # the current options supplied to this invocation of the shell.
$*      # a string containing all the arguments to the shell, starting at $1.
$@      # same as above, except when quoted.

# Notes 
$* and $@ when unquoted are identical and expand into the arguments.
$* # is a single word, comprising all the arguments to the shell, joined together with spaces. For example '1 2' 3 becomes "1 2 3".
$@ # is identical to the arguments received by the shell, the resulting list of words completely match what was given to the shell. For example '1 2' 3 becomes "1 2" "3"

# References http://unixhelp.ed.ac.uk/scrpt/scrpt2.2.2.html