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The Korn
shell is a command interpreter that allows an end user
to type in commands to communicate to the AIX system. By default,
when a user logins, a shell process is started The default AIX
shell is /usr/bin/ksh.
A '-'
is prefixed to the name of the ksh program to indicate that this
shell initially read the contents of the files /etc/environment,
/etc/profile, and $HOME/.profile.
- /etc/environment
specifies the basic environment for all processes
- /etc/profile
specifies variables to be added to the environment by the
shell
- $HOME/.profile
specifies variables specific to user to be added to the environment
by the shell
Other available
shells are...
- /bin/bsh
the Bourne shell
- /bin/csh
the C-shell
- /bin/sh
the Standard shell
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If the ./hushlogin
file exists, it will suppress the displaying of the /etc/motd
file (message of the day file) and the message for unsuccessful
login attempts for that user account.
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The .profile
file is used to personalize a user's account and/or sets the environment
the user will operate under. The following table represents some
examples of settings that can be set in the .profile file.
| Variables |
What
it does |
| PRINTER=mylaser |
Controls
default printer. When you use the lp command
with no additional flags to specify which queue to print to,
by default it will go to the printer queue named after the
equal sign. |
| TMOUT=3600 |
Will
cause an automatic log off after 60 minutes (3600
seconds) if no keyboard activity encountered or no
output is generated to the display after the timeout
period has expired. There is a 60 second pause before the
ksh is exited. |
| ESCDELAY=1000 |
Controls
the amount of time permitted between the ESCape character
and any other components of an ESCape sequence. The AIX
Extended Curses library has a built-in timeout which sets
the maximum amount of time permissible between the receipt
of the ESC character and the second character of the escape
sequence. |
| set
-o noclobber |
Won't
allow you to overwrite a file with the redirection symbol
(eg., cat junk > goodstuff).
To overwrite
the noclobber option when noclobber is enabled, type '>|'
when redirecting output (eg., cat
smit.log >| smit.bck). |
| set
-o ignoreeof |
Disables
^D to logout; you must type exit to exit the shell |
| set
-o vi |
Enable
command line editing/playback using vi commands |
| stty
-olcuc -iuclc -xcase |
-olcuc
maps lower case to upper case on output.
-iuclc=maps upper case to lower case on input.
-xcase won't allow you to login unless in lower case. |
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Assign a name
or an abbreviated name that makes sense or is shorter for a command.
| Examples |
What
it does |
| alias |
Lists
the aliases that are currently defined. |
| alias
"dir=ls" |
Creates
an alias. dir will output
the same contents as the ls
command. |
| unalias
name |
Removes
an alias. unalias dir |
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Executes the
command line directly without creating a new process (PID) (current
shell is overlaid with command specified on the command line).
When the command has finished or is terminated, control is returned
to the init process, thereby logging off the user. Typically you
will see this command used as the last entry in the $HOME/.profile.
| Examples |
What
it does |
| exec
/usr/bin/smit |
Will
execute the System Management Interface Tool (SMIT) program
- overlaying the current shell program |
| Changing
standard input (stdin) |
| exec
<FileNameForInput |
Reassigns
standard input from the keyboard to a file |
| exec
</dev/tty |
Reassigns
standard input back to the keyboard |
| exec
<&- |
Closes
standard input |
| exec
</dev/null |
Associate
standard input to null device |
| Changing
standard output (stdout) |
| exec
>WriteToFileName |
Reassigns
standard output from your terminal display to a file |
| exec
>/dev/tty |
Reassigns
stardard output back to your terminal |
| exec
>&- |
Closes
standard output |
| exec
>/dev/null |
Associate
standard output to null device |
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Contains the
history of user commands executed on the command line for each
login session.
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List the last
16 commands executed from the command line. (Uses .sh_history)
| Examples |
What
it does |
history
! 310
|
Re-executes
the item labled 310 in the .sh_history file |
| -25 |
List
the last 25 commands executed from the command line. Default
number of commands listed is 16. |
| r
vi |
Re-executes
the latest 'vi' session stored in the .sh_history file |
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Sends a signal
to a running process to inform it to do something. Typically you
use the signal KILL to terminate or suspend a process.
| Examples |
What
it does |
| kill
-9 5344 |
Will
terminate the process with a process id (PID) of 5344. A signal
value of -9 means that the signal can't be caught by the application
but is intercepted by AIX to terminate the process in question. |
| kill
-l |
Lists valid signals to use with the kill command. |
| kill
- |
Easy
way to terminate all processes running in the system EXCEPT
your current shell and the /etc/init process. |
| kill
-STOP 3901 |
Suspends
the PID 3901. Execute the ps -elf|grep
3901 command and the status field (marked 'S') will
have a 'T', meaning the process is suspended.. |
| kill
-CONT 3901 |
Resumes
the suspended process whose PID is 3901 |
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Pressing ^Z
will suspend a process. To unsuspend a process, use the fg
command to bring that process to the foreground again or bg
to leave the process running in the background.
| Examples |
What
it does |
| ^Z |
Will
suspend the current PID. Example output: [1] + 8193 Stopped |
| jobs
-l |
List
all current jobs suspended |
| fg
3934 |
Will
bring suspended job PID 3934 to the foreground. If
only one command is listed when jobs -l is executed,
you only need to type fg to bring the only suspended
process back to the foreground. |
| bg
4011 |
Will
run the suspended job with a PID of 4011 in the background
now |
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Set
positional parameters for the current shell.
| Examples |
What
it does |
| set
`date`; echo $1 $2
$3 $4 $5 $6 |
Thu
Nov 14 20:12:47 CST 2002 |
| echo
$6 |
Displays
the year - 2002 |
| set
-o |
Displays
current settings for the set command. |
set
-o noclobber
set +o noclobber |
Won't
allow a user to overwrite a file with the same file name.
Use -o to turn on or +o to turn off |
set
-o vi
set +o vi |
Enable
sers to use 'vi' commands to manipulate command line entry.
Use -o to turn on or +o to turn off |
set
-o xtrace
set +o xtrace |
Displays
commands and their arguments as they are executed. Normally,
you would place the 'set -x' command at the beginning of a
script file. |
| unset
ENV |
Used
to undefine a system variable. Removes the system variable
ENV from your user environment |
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