More UNIX

Table of Contents

Shells
Korn (ksh) Shell
String Operators
Job Control
Text Editing: vi
Text Editing: emacs
Emacs Compilation
Emacs GNU g++ IDE
XEmacs
I/O Redirection
UNIX Error Messages

Shells

Shell Definition

Interface between the user and the operating system.

Different UNIX Shells

Bourne, Korn, C Shell, tcsh, bash, zsh, etc.

Recommended — Korn (ksh) Shell

ksh is a variant of the Bourne Shell.
Provides all features of the Bourne Shell.
Allows access to prior (history) commands with the j, k keys (after <escape>).

Changing Shells

chsh command allows users to switch default login shells.

Long Commands

\ character allows commands to be split across multiple lines.
Shell variable PS2 defines prompt for continued lines.

History

Mechanism for saving recently executed commands (events).
export HISTSIZE = 25 - command to save the last 25 commands.
history —- command to display the history list.
r 3 - executes command number 3 in the history list.
r - re-executes the last executed command.
r prog—- re-executes the most recent command beginning with the string "prog".

Korn (ksh) Shell

Environment Startup File

.profile — contains commands that execute at log in, and that need execute only once.

Sample (simple) profile:

CDPATH=.:..:$HOME
PATH=.:./bin:$HOME/bin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/ucb:\
/usr/local/bin:/usr/bin/X11 
EDITOR=/usr/ucb/vi
ENV=$HOME/.kshrc
EXINIT='set ai nonumber showmatch wrapmargin=72 nowrapscan'
FCEDIT=/usr/ucb/vi
HISTSIZE=32
MAIL=/usr/spool/mail/$USER
PS1="! ${HOST%%.*}> "
SHELL=/usr/bin/ksh
export CDPATH EDITOR ENV EXINIT FCEDIT HISTSIZE HOST MAIL PATH PS1
export SHELL
biff y
tset -I
stty  erase \^? kill \^U intr \^C
umask 0022
alias mail=/usr/ucb/mailx
OSTYPE=`uname`

CDPATH Directories searched by cd command.

EDITOR Sets default editor.

ENV Name of script that is executed at startup.

EXINIT Sets options for ex and vi editors.

FCEDIT Editor used by the fc command.

HISTSIZE Number of history commands available (must be set before ksh is started).

PATH Directories searched for any file (command) name. Most important shell variable.

PS1 Primary prompt string; default is $.

SHELL Name of shell environment.

export Pass the value of shell variables, giving global meaning to them.

tset Initializes terminals, setting the TERM variable.

biff y System notifies user of new mail.

stty erase Sets delete character for command line edits.

umask Sets (eliminates) file default access permissions.

alias Allows commands (and options) to be abbreviated.

.kshrc file

Contains shell commands executed whenever a new Korn shell is instigated.

Sample .kshrc file:

set -o  trackall

Locate commands as they are defined.

Starting and Exiting

ksh — creates a new Korn shell.
exit closes the window or logout (equivalent to <control D>).

String Operators

${varname:-word} If varname exists and isn't null, return its value; otherwise return word.
${varname:=word} If varname exists and isn't null, return its value; otherwise set it to word and then return its value.
${varname:?message} If varname exists and isn't null, return its value; otherwise print varname: followed by message, and abort the current command or script.
${varname:+word} If varname exists and isn't null, return word; otherwise return null.
${varname#pattern} If the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest.
${varname##pattern} If the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest.
${varname%pattern} If the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest.
${varname%%pattern} If the pattern matches the end of the variable's value, delete the longest part that matches and return the rest.

${varname:-word}	If varname exists and isn't null, return its value; otherwise return word.
${varname:=word}	If varname exists and isn't null, return its value; otherwise set it to word and then return its value.
${varname:?message}	If varname exists and isn't null, return its value; otherwise print varname: followed by message, and abort the current command or script.
${varname:+word}	If varname exists and isn't null, return word; otherwise return null.
${varname#pattern}	If the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest.
${varname##pattern}	If the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest.
${varname%pattern}	If the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest.
${varname%%pattern}	If the pattern matches the end of the variable's value, delete the longest part that matches and return the rest.

Job Control

Concurrent Execution

Commands that allow control over multiple processes (programs) that are executing concurrently.
Foreground - the current process that is attached to the user’s terminal.
Background - unattached processes executing without being attached to a terminal (batch commands, etc.).
command & - any shell command can be followed by an & (before the return) to run the command in the background.

Jobs

Commands executed under the Korn shell are given a job number.
jobs - command that lists the current jobs.

[1]  + Stopped             spell termpaper
[2]  - Running             find /usr -name main.exe -print &

Management

fg %number - moves a background job to the foreground.
<control z> - suspends the current job and moves it to the background.
bg %number - resumes execution of a job in the background.
ps - lists the running processes.

  PID TT STAT   TIME COMMAND
12360 p0 S      0:01 -ksh (ksh)
12372 p0 I      0:00 main
12425 p0 R      0:00 ps -x

kill -STOP %number - suspends a running background job.
kill %number - terminates the process with the corresponding job number.
kill PID - terminates the process with the corresponding process id.

Text Editing: vi

To execute vi:

vi filename If there is no file, vi creates the file.

vi can be in one of the following three modes:

vi command mode - for cursor movement and text deletion.
vi input mode - for entering text.
vi ex mode - all commands starting with a colon.

When vi is first loaded, it is in the command mode. This means that all keystrokes entered are interpreted as commands. To return to command mode from input mode, hit <ESCAPE>.

vi reference sheet - in command mode

Description	Command Code
Move one space to the right	Space, l, or right arrow
Move one space to the left	h, or left arrow
Move down one line	j, or down arrow
Move up one line	k , or up arrow
Move one word to the right	w, or W
Move one word to the left	b, or B
Move to beginning of line	0
Move to end of line	$
Move to top of screen	H
Move to middle of screen	M
Move to bottom of screen	L
Save contents to file	:w
Quit file	:q
Quit vi, saving file only if changes were made	:x
Save file and quit vi	:wq
Save contents to file and quit vi	ZZ
Toggle between uppercase and lowercase	~
Delete back one character	X
Delete character under cursor	x
Delete line	dd
Delete word	dw

See the vi notes for more commands and details.

The following commands leave vi in input mode. The table gives the position where the text is inserted.

Description	Insert Text
Before cursor	i
At beginning of line	I
After cursor	a
At end of line	A
After current line	o
Before current line	O

Text Editing: emacs

emacs

To execute emacs:

emacs filename If there is no file, emacs creates the file

GNU Emacs Novice Reference Sheet

Note that ``C-x" means ``hold down the Control key, and type the x key". ``M-x" means "type the ESC key, then type the x key". Alternatively, if your terminal has a Meta-key, then ``M-x" means "hold down the Meta key, and type the x key".

Description	Command Code
Exit Emacs	C-x C-c
Suspend Emacs	C-z
Get help	C-h
Save a file	C-x C-s
Visit a new file	C-x C-v
Visit another buffer	C-x b
Abort a command	C-g
Down one screen-full	C-v
Up one screen-full	M-v
Forward one character	C-f
Forward one word	M-f
Back one character	C-b
Back one word	M-b
Down to next line	C-n
Up to previous line	C-p
Go to beginning of line	C-a
Go to end of line	C-e
Go to begining of file	M-<
Go to end of file	M->
Set mark (begin region)	C-@ or C-SPACE
Go to mark	C-x C-x
Delete previous character (back)	DEL
Delete current character (forward)	C-d
Delete previous word (back)	M-DEL
Delete next work (forward)	M-d
Kill rest of line (send to kill buffer)	C-k
Delete region (from mark) (send to kill buffer)	C-w
Yank back kill buffer	C-y
Incremental search forward	C-s
Incremental search backward	C-r
Exit incremental search	ESC
Abort incremental search	C-g
Get rid of extra windows	C-x 1
Split window in two	C-x 2
Move cursor to other window	C-x o
Start a shell window	M-x shell
Run the compiler	M-x compile
Move to next compiler error	C-x `

Emacs Compilation

g++ GNU C++ compiler

esc -x compile — runs the compiler under emacs.
First compilation results in emacs providing the default make -k as the compilation command.
Delete (backspace) default compilation command and replace with the g++ compiler command:
g++ filename.cc -g -o executable
-g option forces debugging code inclusion.
-o option allows an executable name to be specified.

Emacs GNU g++ IDE

Integrated Development Environment

^x` — positions cursor on line containing next error
(control x grave character — not single quote, below tilde char)
emacs displays error message from g++ in the C++ window
the GNU debugger (gdb) can also be controlled easily from within emacs

XEmacs

THE Most Powerful Editor? in the World!

http://xemacs.cs.uiuc.edu/

Features

Color coding of Programming language keywords
Allows picture editing
WWW browser
etc., etc., etc........

I/O Redirection

Devices in UNIX are represented as files:

e.g., /dev/console.

UNIX commands receive their input from the standard input (stdin) and send their output to the standard output (stdout), by default these files are the console or terminal.

Shells allow input/output (I/O) to be redirected from/to other devices, thus UNIX commands are unaware from what device their input may originate or to what device their output may be sent.

command name [args] > filename

The output redirection symbol, > , sends the command's output to the specified file instead of the console/terminal screen.

ls -al > ls.out

The file ls.out is created if it does not exist (or emptied and overwritten if it exists prior to command execution) and sent the directory listing.

Programs that send their output to the console/terminal may also be redirected.

progxcs1044 > px.out

This allows execution results of a program to be captured in a file.

The output redirection symbol >> appends the output to a file, rather than overwriting an existing file

progxcs1044 >> px.out

The results of several program runs can thus be saved in a single file px.out.

command name [args] < filename

The input redirection symbol, < , sends the command input from the specified file instead of the console/terminal keyboard.

progxcs1044 < px.inp > px.log

This allows program execution with several data sets very easily.

The input redirection symbol << is known as the "here is" symbol, and provides a mechanism for reading data from the same file as a command is contained in.

progxcs1044 > pt.out << !
first line of data
second line of data
. . .
last line of data
!

The string following <<, in this example an exclamation point, when appearing at the beginning of a line, terminates the data input. The ! here logically acts like an end-of-file (<control-D>).

Pipes | are the logical extension of I/O redirection.

Pipes allow the stdout of one program to become the stdin of another program.

ls -al | more

The above command allows the viewing of the long listing of a large directory one screen at a time.

ls -al > ls.out

more < ls.out

rm ls.out

The above I/O redirection is an equivalent set of commands, but requires the ls.out temporary file.

UNIX Error Messages

Actual UNIX csh responses (system dependent).

% "How poorly would you rate the UNIX user interface?
Unmatched ".

% rm congressional-ethics
rm: congressional-ethics nonexistent

% ar m God
ar: God does not exist.

% [Where is Jimmy Hoffa?
Missing ].

% ^How did the sex  change^ operation go?
Modifier failed.

% make love
Make: don't know how to make love. Stop.

% got a light?
No match.

%man: why did you get a divorce?
man: Too many arguments.

% ^What is saccharine?
Bad substitute.

$ drink <bottle; opener
bottle: cannot open
opener: not found

Last modified: Mon Nov 3 09:41:41 EST 1997