B.3. bash versus sh

B.3. bash versus sh

The Bourne Again ( bash ) shell has the following features not found in the traditional Bourne shell ( sh ).

• Formatting the prompts

• History ( csh style)

• Aliases

• A built-in command line editor ( emacs or vi ) for editing the command line

• Directory manipulation with pushd and popd

• Csh- type job control to stop or run jobs in the background, bring them to the foreground, etc. with command such as bg , fg , Ctrl-Z, etc.

• Tilde, brace , and parameter expansion

• Key bindings to customize key sequences

• Advanced pattern matching

• Arrays

• The select loop (from Korn shell)

• Many new built-in commands

Feature	C/TC	Bourne	Bash	Korn
Variables :
Assigning values to local variables	set x = 5	x=5	x=5	x=5
Assigning variable attributes			declare or typeset	typeset
Assigning values to environment variables	setenv NAME Bob	NAME='Bob'; export NAME	export NAME='Bob'	export NAME='Bob'
Read-Only Variables:
Accessing variables	echo $NAME set var = net echo ${var}work network	echo $NAME var=net echo ${var}work network	echo $NAME var=net echo ${var}work network	echo $NAME or print $NAME var=net print ${var}work network
Number of characters	echo $%var (tcsh only)	N/A	${#var}	${#var}
Special Variables:
PID of the process	$$	$$	$$	$$
Exit status	$status, $?	$?	$?	$?
Last background job	$! (tcsh only)	$!	$!	$!
Arrays:
Assigning arrays	set x = (a b c)	N/A	y[0]='a'; y[2]='b'; y[2]='c' fruit=(apples pears peaches plums)	y[0]='a'; y[1]='b'; y[2]='c' set A fruit apples pears plums
Accessing array elements	echo $x[1] $x[2]	N/A	echo ${y[0]} ${y[1]}	print ${y[0]} ${y[1]}
All elements	echo $x or $x[*]	N/A	echo ${y[*]}, ${fruit[0]}	print ${y[*]}, ${fruit[0]}
No. of elements	echo $#x	N/A	echo $y{#[*]}	print ${#y[*]}
Command Substitution:
Assigning output of command to variable	set d = `date`	d=`date`	d=$(date) or d=`date`	d=$(date) or d=`date`
Accessing values	echo $d echo $d[1], $d[2], ... echo $#d	echo $d	echo $d	print $d
Command Line Arguments (Positional Parameters):
Accessing	$argv[1], $argv[2] or , ...	$1, $2 ... $9	$1, $2, ... ${10} ...	$1, $2, ... ${10} ...
Setting positional parameters	N/A	set a b c set `date` echo ...	set a b c set `date` or set $(date) echo ...	set a b c set `date` or set $(date) print ...
No. of command line arguments	$#argv $# (tcsh)	$#	$#	$#
No. of characters in $arg[number]	$%1, $%2, (tcsh)	N/A	N/A	N/A
Metacharacters for Filename Expansion:
Matches for:
Single character	?	?	?	?
Zero or more characters	*	*	*	*
One character from a set	[abc]	[abc]	[abc]	[abc]
One character from a range of characters in a set	[a “c]	[a “c]	[a-c]	[a “c]
One character not in the set	N/A (csh) [^abc] (tcsh)	[!abc]	[!abc]	[!abc]
? matches zero or one occurrences of any pattern in the parentheses. The vertical bar represents an OR condition; e.g., either 2 or 9. Matches abc21, abc91, or abc1.			abc?(29)1	abc?(29)1
Filenames not matching a pattern	^pattern (tcsh)
I/O Redirection and Pipes:
Command output redirected to a file	cmd > file	cmd > file	cmd > file	cmd > file
Command output redirected and appended to a file	cmd >> file	cmd >> file	cmd >> file	cmd >> file
Command input redirected from a file	cmd < file	cmd < file	cmd < file	cmd < file
Command errors redirected to a file	(cmd > /dev/tty)>&errors	cmd 2>errors	cmd 2> file	cmd 2> errors
Output and errors redirected to a file	cmd >& file	cmd > file 2>&1	cmd >& file or cmd &> file or cmd > file 2>&1	cmd > file 2>&1
Assign output and ignore noclobber	cmd > file	N/A	cmd > file	cmd > file
here document	cmd << EOF input EOF	cmd << EOF input EOF	cmd << EOF input EOF	cmd << EOF input EOF
Pipe output of one command to input of another command	cmd cmd	cmd cmd	cmd cmd	cmd cmd
Pipe output and error to a command	cmd & cmd	N/A	N/A	(See coprocesses)
Coprocess	N/A	N/A	N/A	command &
Conditional statement	cmd && cmd cmd cmd	cmd && cmd cmd cmd	cmd && cmd cmd cmd	cmd && cmd cmd cmd
Reading from the Keyboard:
Read a line of input and store into variable(s)	set var = $< set var = 'line'	read var read var1 var2...	read var read var1 var2... read read -p prompt read -a arrayname	read var read var1 var2... read read var?"Enter value"
Arithmetic:
Perform calculation	@ var = 5 + 1	var=`expr 5 + 1`	((var = 5 + 1)) let var=5+1	((var = 5 + 1)) let var=5+1
Tilde Expansion:
Represent home directory of user	~username	N/A	~username	~username
Represent home directory	~	N/A	~	~
Represent present working directory	N/A	N/A	~+	~+
Represent previous working directory	N/A	N/A	~-	~ “
Aliases:
Create an alias	alias m more	N/A	alias m=more	alias m=more
List aliases	alias		alias, alias -p	alias, alias “t
Remove an alias	unalias m	N/A	unalias m	unalias m
History:
Set history	set history = 25	N/A	automatic or HISTSIZE=25	automatic or HISTSIZE=25
Display numbered history list	history		history, fc -l	history, fc “l
Display portion of list selected by number	history 5		history 5	history 5 10 history 5
Re-execute a command	!! (last command) !5 (5th command) !v (last command starting with v)		!! (last command) !5 (5th command) !v (last command starting with v)	r (last command) r5 (5th command) r v (last command starting with v)
Set interactive editor	N/A (csh) bindkey -v or bindkey -e (tcsh)	N/A	set -o vi set -o emacs	set -o vi set -o emacs
Signals:
Command	onintr	trap	trap	trap
Initialization Files:
Executed at login	.login	.profile	.bash_profile	.profile
Executed every time the shell is invoked	. cshrc	N/A	BASH_ENV=.bashrc (or other filename) (bash 2.x) ENV=.bashrc	ENV=. kshrc (or other filename)
Functions:
Define a function	N/A	fun() { commands; }	function fun { commands; }	function fun { commands; }
Call a function	N/A	fun fun param1 param2 ...	fun fun param1 param2 ...	fun fun param1 param2 ...
Programming Constructs:
if conditional	if (expression) then commands endif if { (command) } then commands endif	if [ expression ] then commands fi if command then commands fi	if [[ string expression ]] then commands fi if ((numeric expression)) then commands fi	if [[ string expression ]] then commands fi if ((numeric expression)) then commands fi
if/else conditional	if (expression) then commands else commands endif	if command then commands else ... fi	if command then commands else ... fi	if command then commands else ... fi
if/else/elseif conditional	if (expression) then commands else if (expression) then commands else commands endif	if command then commands elif command then commands else commands fi	if command then commands elif command then commands else commands fi	if command then commands elif command then commands else commands fi
goto	goto label ... label:	N/A	N/A	N/A
switch and case	switch ("$value") case pattern1: commands breaksw case pattern2: commands breaksw default: commands breaksw endsw	case "$value" in pattern1) commands ;; pattern2) commands ;; *) commands ;; esac	case "$value" in pattern1) commands ;; pattern2) commands ;; *) commands ;; esac	case "$value" in pattern1) commands ;; pattern2) commands ;; *) commands ;; esac
Loops:
while	while (expression) commands end	while command do command done	while command do command done	while command do commands done
for/foreach	foreach var (wordlist) commands end	for var in wordlist do commands done	for var in wordlist do commands done	for var in wordlist do commands done
until	N/A	until command do commands done	until command do commands done	until command do commands done
repeat	repeat 3 "echo hello" hello hello hello	N/A	N/A	N/A
select	N/A	N/A	PS3="Please select a menu item" select var in wordlist do commands done	PS3="Please select a menu item" select var in wordlist do commands done