Bash – Special Shell Variables

Special Shell Variables

Variable	Meaning
`$0`	Filename of script
`$1`	Positional parameter #1
`$2 - $9`	Positional parameters #2 – #9
`${10}`	Positional parameter #10
`$#`	Number of positional parameters
`"$*"`	All the positional parameters (as a single word) *
`"$@"`	All the positional parameters (as separate strings)
`${#*}`	Number of command line parameters passed to script
`${#@}`	Number of command line parameters passed to script
`$?`	Return value
`$$`	Process ID (PID) of script
`$-`	Flags passed to script (using set)
`$_`	Last argument of previous command
`$!`	Process ID (PID) of last job run in background

* Must be quoted, otherwise it defaults to « $@« .

Benjamin Baudouin