Linux Shell Tips and Tricks

 

 

---

 

Overview

 

Redirecting STDERR

Redirects stderr to stdout.

program 2>&1

Redirect both stdout and sterr to log.txt.

program >log.txt 2>&1 log.txt

 

Escaped Characters

   #!/bin/bash"

    echo "\v\v\v\v"                           # Prints \v\v\v\v
    echo -e "\v\v\v\v"                        # Prints 4 vertical tabs.
    echo -e "\042"                            # Prints " (quote, octal ASCII character 42).
    echo $'\n'                                # Prints line feed
    echo $'\a'
    echo $'\t \042 \t'                        # Quote (") framed by tabs.
    quote=$'\042'                             # " assigned to a variable.

    echo "$quote This is a quoted string, $quote and this lies outside the quotes."

    triple_underline=$'\137\137\137'          # 137 is octal ASCII code for "_".

    echo "$triple_underline UNDERLINE $triple_underline"

    ABC=$'\101\102\103\010'                   # 101, 102, 103 are octal A, B, C.
    echo $ABC
    escape=$'\033'                            # 033 is octal for escape.
    echo "\"escape\" echoes as $escape"

 

Echoing Weird Variables

#!/bin/bash"
 var="'(]\\{}\$\""
 echo $var        # '(]\{}$"
 echo "$var"      # '(]\{}$"     Doesn't make a difference.

 IFS='\'
 echo $var        # '(]\{}$"     \ converted to space.
 echo "$var"      # '(] {}$"

 # Examples above supplied by S.C.

 exit 0

Single quotes (' ') operate similarly to double quotes, but do not permit referencing variables, since the special meaning of $ is turned off. Within single quotes, every special character except ' gets interpreted literally. Consider single quotes ("full quoting") to be a stricter method of quoting than double quotes ("partial quoting").

 

Showing Directory/Machine Name In The Title Bar Of Your Shell Windows

To show the current directory, add the following three lines to your $HOME/.cshrc-linux-$user file:

alias cd ' chdir \!* && header `dirs` ' 
alias header ' echo -n "\033]2;\!*\007\033]1;\007" ' 
header `dirs`

Now open a new window, or manually execute source $HOME/.cshrc-linux-$user. You should now see the current directory in the title bar of the window.

To show the machine as well as the directory in machine:directory format, use the following three lines instead:

alias cd ' chdir \!* && header `hostname`":"`dirs` ' 
alias header ' echo -n "\033]2;\!*\007\033]1;\007" ' 
header `hostname`":"`dirs` 

 

Modifying The Colors In Directory Listings

You will notice that there are default colors in directory listings for certain types of files; executables are green, directories are dark blue, symbolic links are light blue. This is accomplished by the line alias ls "ls -CF --color=tty" in the system /etc/csh.cshrc file.

If you don't want any colors at all, either place the line "unalias ls" in your $HOME/.cshrc-linux-$user file (create the file if you don't have it), or redefine an alias for ls to list things the way you want, e.g. alias ls "ls -F"

To modify the colors, you need to set the LS_COLORS environment variable. for more details.

 

Customizing Your Prompt in Linux

Execute the following commands to give the following prompts:

Comands below will colorize your prompt. Try one of the following:

set prompt="%m:%{^[[36;1m%}%/%{^[[0m%}> "
set prompt="%m:%{^[[34;1m%}%/%{^[[0m%}> "
set prompt="%m:%{^[[31;1m%}%/%{^[[0m%}> "
(Make the colors a little darker by changing the  ;1m to ;3m) 
set prompt="%m$ "
set prompt="%n@%m: "
set prompt="%n@%{^[[34;1m%}%m%{^[[0m%} "

Place the appropriate command in your .cshrc-linux-$user file (create the file if you don't already have it).

 

What "dot" files do the various shells use (configuration files)

Although this may not be a complete listing, this provides the majority of information.  

csh
Some versions have system-wide .cshrc and .login files.  Every
version puts them in different places.

Start-up (in this order):
 .cshrc   - always; unless the -f option is used.
 .login   - login shells.

Upon termination:
 .logout  - login shells.

Others:
 .history - saves the history (based on $savehist).

tcsh
Start-up (in this order):
 /etc/csh.cshrc - always.
 /etc/csh.login - login shells.
 .tcshrc        - always.
 .cshrc         - if no .tcshrc was present.
 .login         - login shells

Upon termination:
 .logout        - login shells.

Others:
 .history       - saves the history (based on $savehist).
 .cshdirs       - saves the directory stack.

sh
Start-up (in this order):
 /etc/profile - login shells.
 .profile     - login shells.

Upon termination:
 any command (or script) specified using the command:
    trap "command" 0

ksh
Start-up (in this order):
 /etc/profile - login shells.
 .profile     - login shells; unless the -p option is used.
 $ENV         - always, if it is set; unless the -p option is used.
 	  /etc/suid_profile - when the -p option is used.

Upon termination:
 any command (or script) specified using the command:
    trap "command" 0

bash
Start-up (in this order):
 /etc/profile  - login shells.
 .bash_profile - login shells.
 .profile      - login if no .bash_profile is present.
 .bashrc       - interactive non-login shells.
 $ENV          - always, if it is set.

Upon termination:
 .bash_logout  - login shells.

Others:
 .inputrc      - Readline initialization.

zsh
Start-up (in this order):
 .zshenv   - always, unless -f is specified.
 .zprofile - login shells.
 .zshrc    - interactive shells, unless -f is specified.
 .zlogin   - login shells.

Upon termination:
 .zlogout  - login shells.

rc
Start-up:
 .rcrc - login shells

 

Find out which user or process has a file open or is using a particular file system (so that you can unmount it?)

Use fuser (system V), fstat (BSD), ofiles (public domain) or pff (public domain). These programs will tell you various things about processes using particular files.

A port of the 4.3 BSD fstat to Dynix, SunOS and Ultrix can be found in archives of comp.sources.unix, volume 18.

pff is part of the kstuff package, and works on quite a few systems. Instructions for obtaining kstuff are provided in question 3.10.

You can also use lsof to list open files.

If you are unable to unmount a file system for which above tools do not report any open files make sure that the file system that you are trying to unmount does not contain any active mount points (df(1)).

 

How to rename hidden files (.foo to .bar)

 C Shell:
 foreach f ( *.foo )
 	set base=`basename $f .foo`
 	mv $f $base.bar
 end

 Bourne Shell:
 for f in *.foo; do
 	base=`basename $f .foo`
 	mv $f $base.bar
 done

Some shells have their own variable substitution features, so instead of using
"basename", you can use simpler loops like:

C Shell:
 foreach f ( *.foo )
 	mv $f $f:r.bar
 end

Korn Shell:
 for f in *.foo; do
 	mv $f ${f%foo}bar
 done

If you don't have "basename" or want to do something like renaming foo.* to
bar.*, you can use something like "sed" to strip apart the original file name in
other ways, but the general looping idea is the same.  You can also convert
file names into "mv" commands with 'sed', and hand the commands off to
"sh" for execution.  Try

 ls -d *.foo | sed -e 's/.*/mv & &/' -e 's/foo$/bar/' | sh

 

Removing a file whose name begins with a "-"

rm ./-filename 

 

How to find which libraries a program requires?

To find out which shared libraries a program requires, type

ldd `which program`

 

How to find out what process is eating the most memory?

ps -aux | sort +4n

 

Customizing your directory colors (linux)

All you need to do is add the following line to your /etc/bashrc file.

eval `dircolors /etc/DIR_COLORS`

And then all of the color configuration can be found in the file /etc/DIR_COLORS

 

HOW TO EXECUTE A TEXT OR BINARY FILE

You can try the following builtin command:

source file_name

To execute file directly make it executable first:

chmod +rx file_name

Now execute it with absolute or relative path such as:
/home/user1/file_name
./file_name
Or with shell:
ksh file_name

 

Some examples on using stty command:

stty 9640 		# set the terminal bit rate to 9640 bps
stty rows 30 columns 75 	# set the terminal window size to 30 rows and
 			# 75 columns
stty erase  		# set backspace button
stty erase \^H 		# set backspace button
stty erase kill  	# set CTRL+X as your kill character instead of @
stty erase kill \^X 	# set CTRL+X as your kill character instead of @
stty eof  		# set CTRL+C as end-of-file character
stty eof \^C 		# set CTRL+C as end-of-file character
stty ek 			# set reset your erase and kill character back
 			# to # and @
stty -a 			# check your terminal settings
stty sape 		# set terminal to use the most common options in
 			# case of troubles

 

Show working directory in command prompt

PS1="\$PWD $ "

If you are using csh:

set prompt="${cwd:t}%" 

 

Some examples on using date command:

date 		# shows corrent date and time
date DDMMhhmmYY 	# sets current date and time 

 

Some examples on using ls command:

ls # lists contents in current dir
ls -a # lists contents in current dir including hidden files
ls -l # lists contents in current dir in long form
ls -h # lists contents in current dir with sizes in kb/mb (linux) 

 

Some examples on using df/bdf command:

bdf # show mounted filesystems
df # show mounted filesystems (linux)
df -h # show mounted filesystems with sizes in kb/mb (linux) 

 

Some examples on using more command:

more file_name # lists contents of a file
more * 	# lists contents of all files in current directory 

 

Some examples on using rm command:

rm file 	# removes file
rm -R -i dir # interractively removes directory recursively
 	# (including hidden and sistem files)
rm -R -f dir # removes directory with option force (noninterractive)
rm -R -f * # irreversably removes everything on the current path  

 

Some examples on using cd command:

cd  	# puts you into your home directory
cd /  	# puts you to the root directory
cd - 	# puts you to the directory last accessed
cd ~/data # puts you to the directory data in your home directory
cd ../dir2  # puts you from the current subdirectory to another
 	# (dir2) at the same directory level

 

Finding Out More Terminal Settings

stty  -a 

 

Resetting Terminal Characteristics

Try some of the following
clear
tput  clear
tput  reset
tput  init
reset
stty  sane
eval  `resize` 

 

Saving Your Terminal Characteristics

stty  -g > $HOME/.stty  

 

Restoring Saved Terminal Characteristics

stty  `cat  $HOME/.stty`

 

Define Default Login Shell

chsh  sh 

 

Define Shell Command-Line Editing Mode

Use Emacs or vi in command line to edit commands>

Emacs editing mode:
set  -o emacs

Vi editing mode:
set  -o vi 

 

Show Last Entries in Command History List

fc  -l 

 

Show Total Command History List

fc  -l 1

or

history 

 

Saving Shell Output Into File

script
...
commands
...
exit 

A file containing everything printed on the console will now be typescript

 

Show Jobs

jobs 

 

Kill All My Jobs Except This One

kill  -TERM -1 

 

Kill More Jobs At the Same Time

On System V UNIXes:

ps  -ef | awk  '/pattern/  print $2 ' | xargs  kill  -9 

 

Show status of running jobs

On System V UNIXes:

ps  -elf | cut  -c 5-15,84- 

 

Show Last 100 Commands

fc  -l -100 

 

Stop Background Job

Automatically stop background jobs if they write to screen

tty  -tostop

or

kill  %job_number 

 

Displaying Most Active Processes

On BSD UNIXes:
ps  -aux | head  -5
top
yamm
ps  -aux | sort  +4n
ps  -aux | sort  +5n 

 

Displaying All Processes

On System V UNIXes:
ps  -ef

On BSD UNIXes:
ps  -aux

 

Displaying All Zombie Processes

On System V UNIXes:

ps  -el | grep  " Z " 

 

Displaying All Running Processes

ps  -el | grep  " R " 

 

Timing Programs

time  program arguments 

 

Checking System Load Time

uptime 

 

Be Nice To Other Users With Time Consuming Job

Run a command at non-default priority

nice  f77  -o test test.f > f77.out 

 

Changing Job Priority

Example:

renice  5 -p pid 

 

CHANGE PERMISSIONS ON ALL FILES IN DIRECTORY

chmod -R 755 dir_name 

 

WHEN THE SPECIFIC USER WAS LAST LOGGED IN ?

To see all logging informations for specific user try the following:

last user_name |more 

---