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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).
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 |
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).
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 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.