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


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C.1. 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.


Table C-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)

$*

All arguments as a simple word

#

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


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C.2. 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).


imageShell 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 C-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.


See Appendix B if you are having difficulties to assimilate shell commands.

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