Bash Guide for Beginners Appendix A. Shell Features

This document gives an overview of common shell features (the same in every shell flavour) and differing shell features (shell specific features).

Common features

The following features are standard in every shell. Note that the stop, suspend, jobs, bg and fg commands are only available on systems that support job control.

A-1. Common Shell Features

Command	Meaning
>	Redirect output
>>	Append to file
<	Redirect input
<<	"Here" document (redirect input)
|	Pipe output
&	Run process in background.
;	Separate commands on same line
*	Match any character(s) in filename
?	Match single character in filename
[ ]	Match any characters enclosed
( )	Execute in subshell
` `	Substitute output of enclosed command
" "	Partial quote (allows variable and command expansion)
' '	Full quote (no expansion)
\	Quote following character
$var	Use value for variable
$$	Process id
$0	Command name
$n	nth argument (n from 0 to 9)
#	Begin comment
bg	Background execution
break	Break from loop statements
cd	Change directories
continue	Resume a program loop
echo	Display output
eval	Evaluate arguments
exec	Execute a new shell
fg	Foreground execution
jobs	Show active jobs
kill	Terminate running jobs
newgrp	Change to a new group
shift	Shift positional parameters
stop	Suspend a background job
suspend	Suspend a foreground job
time	Time a command
umask	Set or list file permissions
unset	Erase variable or function definitions
wait	Wait for a background job to finish

Differing features

The table below shows major differences between the standard shell (sh), Bourne Again SHell (bash), Korn shell (ksh) and the C shell (csh).

Note: Shell compatibility Since the Bourne Again SHell is a superset of sh, all sh commands will also work in bash - but not vice versa. bash has many more features of its own, and, as the table below demonstrates, many features incorporated from other shells. Since the Turbo C shell is a superset of csh, all csh commands will work in tcsh, but not the other way round.

Table A-2. Differing Shell Features

sh	bash	ksh	csh	Meaning/Action
$	$	$	%	Default user prompt
	>|	>|	>!	Force redirection
> file 2>&1	&> file or > file 2>&1	> file 2>&1	>& file	Redirect stdout and stderr to file
	{ }		{ }	Expand elements in list
`command`	`command` or $(command)	$(command)	`command`	Substitute output of enclosed command
$HOME	$HOME	$HOME	$home	Home directory
	~	~	~	Home directory symbol
	~+, ~-, dirs	~+, ~-	=-, =N	Access directory stack
var=value	VAR=value	var=value	set var=value	Variable assignment
export var	export VAR=value	export var=val	setenv var val	Set environment variable
	${nnnn}	${nn}		More than 9 arguments can be referenced
"$@"	"$@"	"$@"		All arguments as separate words
$#	$#	$#	$#argv	Number of arguments
$?	$?	$?	$status	Exit status of the most recently executed command
$!	$!	$!		PID of most recently backgrounded process
$-	$-	$-		Current options
. file	source file or . file	. file	source file	Read commands in file
	alias x='y'	alias x=y	alias x y	Name x stands for command y
case	case	case	switch or case	Choose alternatives
done	done	done	end	End a loop statement
esac	esac	esac	endsw	End case or switch
exit n	exit n	exit n	exit (expr)	Exit with a status
for/do	for/do	for/do	foreach	Loop through variables
	set -f, set -o nullglob|dotglob|nocaseglob|noglob		noglob	Ignore substitution characters for filename generation
hash	hash	alias -t	hashstat	Display hashed commands (tracked aliases)
hash cmds	hash cmds	alias -t cmds	rehash	Remember command locations
hash -r	hash -r		unhash	Forget command locations
	history	history	history	List previous commands
	ArrowUp+Enter or !!	r	!!	Redo previous command
	!str	r str	!str	Redo last command that starts with "str"
	!cmd:s/x/y/	r x=y cmd	!cmd:s/x/y/	Replace "x" with "y" in most recent command starting with "cmd", then execute.
if [ $i -eq 5 ]	if [ $i -eq 5 ]	if ((i==5))	if ($i==5)	Sample condition test
fi	fi	fi	endif	End if statement
ulimit	ulimit	ulimit	limit	Set resource limits
pwd	pwd	pwd	dirs	Print working directory
read	read	read	$<	Read from terminal
trap 2	trap 2	trap 2	onintr	Ignore interrupts
	unalias	unalias	unalias	Remove aliases
until	until	until		Begin until loop
while/do	while/do	while/do	while	Begin while loop

The Bourne Again SHell has many more features not listed here. This table is just to give you an idea of how this shell incorporates all useful ideas from other shells: there are no blanks in the column for bash. More information on features found only in Bash can be retrieved from the Bash info pages, in the "Bash Features" section.

More information:

You should at least read one manual, being the manual of your shell. The preferred choice would be info bash, bash being the GNU shell and easiest for beginners. Print it out and take it home, study it whenever you have 5 minutes.