UNIX/Linux script to set or update the password for multiple users

Example:

Sample users name: dummy1, dummy2, dummy3, dummy4 and dummy5

for counter in {1..5}; do echo "dummy$counter" | passwd dummy$counter --stdin ; done


NOTE: {1..5} syntax will not work in certain shell. But it will work definitely in bash.

UNIX/Linux Shell Script to delete multiple users

Example 1:

To delete the users: dummy1, dummy2, dummy3, dummy4 and dummy5

for  counter in {1..5}; do userdel dummy$counter; done

It can also be written as,

for counter in {1..5}
 do 
       userdel dummy$counter
 done

NOTE: {1..5} syntax will not work in certain shell. But it will work definitely in bash.

Example 2:

cat > user.list
vijay
sanjay
ajay
sujay

for  user in `cat  user.list`;do userdel $user;done

UNIX/Linux Shell script to create multiple users

Example 1:

NOTE: {1..5} syntax will not work in certain shell. But it will work definitely in bash.

Example 2:

cat > user.list
vijay
sanjay
ajay
sujay

for user in `cat user.list`;do useradd $user;done

grep -i jay /etc/passwd | cut -d: -f1
vijay
sanjay
ajay
sujay

How to grep recursively in Solaris?

In Solaris, Solaris grep will not provide recursive option -r to search a pattern recursively. But solaris provides another command called ggrep to search recursively. But ggrep location is normally not included in the PATH variable.

[vjsujay@cheetah:/home/vjsujay]$which ggrep
no ggrep in /usr/bin /bin /usr/sbin /sbin /usr/local/bin

[vjsujay@cheetah:/home/vjsujay]$ls -l /usr/sfw/bin/ggrep
-r-xr-xr-x   3 root     bin       125664 Jan 23  2005 /usr/sfw/bin/ggrep
[vjsujay@cheetah:/home/vjsujay]$

Example for recursive grep using ggrep in Solaris:

[vjsujay@cheetah:/home/vjsujay/sp]$ /usr/sfw/bin/ggrep -R 'apple' *
file.txt:apple
file3.txt:apple orange
jsk/jsk.txt:apple
[vjsujay@cheetah:/home/vjsujay/sp]$

How to find the current shell in UNIX Solaris Linux?

This method works perfectly in any shell.

NOTE: $$ holds the process id of current shell.

[penguin@cheetah:/home/penguin]#ps | grep -i `echo $$`
 18530             0:00 ksh

[penguin@cheetah:/home/penguin]#bash
bash-3.00$ ps | grep -i `echo $$`
 18574 pts/196     0:00 bash

bash-3.00$ csh
cheetah% ps | grep -i `echo $$`
 18578 pts/196     0:00 csh

cheetah% tcsh
> ps | grep -i `echo $$`
 18590             0:00 tcsh

What is meant by Pipe and Filter in Unix or Linux?

PIPE:

Pipe is a way of passing data from standard output of one process to standard input of another process.

Filter:

It is a program that by default reads from standard input and writes to standard output.

How to list only hidden files in UNIX?

ls -1A | grep '^\.'

Eg:


[vjsujay@cheetah:/home/vjsujay]#ls -1A | grep '^\.'
.profile
.recently-used
.sh_history
.softwareupdate
.ssh
[vjsujay@cheetah:/home/vjsujay]#

[vjsujay@cheetah:/home/vjsujay]#ls -1a | grep '^\.'

.

..

.profile

.recently-used

.sh_history

.softwareupdate

.ssh

[vjsujay@cheetah:/home/vjsujay]#

FYI.

-a will list hidden files along with default directories single dot(.) and double-dot(..)
-A will list hidden files without single dot and double dot

How to update and replace files in a tar archive?

Question 1: How to update an existing tarball contents with newfile(s)?

Answer: We have to use the function ‘u’ to update newfile(s) to an existing tarball.

Question 2: How to replace an existing tarball contents with newfile(s)?

Answer: We have to use the function ‘r’ to replace newfile(s) to an existing tarball.

I am providing the definition of function update(u) and replace(c) as per solaris man page.

Function letters           Function

r                                  Replace. The named files are written at the end of  the tarfile

u                                  Update. The named files are written at the end  of  the tarfile  if  they are not already in the tarfile, or if they have been modified since last written to that tar-file.

Example:

[st39422@dios8:/home/st39422]#ls -l fileABC.tar Aiszipped.zip Biszipped.zip

-rw-r--r--   1 st39422  users    7486342 Aug  8 14:19 Aiszipped.zip

-rw-r--r--   1 st39422  users    11256018 Aug  8 14:19 Biszipped.zip

-rw-r--r--   1 st39422  users       8192 Aug  6 12:55 fileABC.tar

Creation of a tarball: AB.tar

[st39422@dios8:/home/st39422]#tar -cvf AB.tar Aiszipped.zip Biszipped.zip

a Aiszipped.zip 7311K

a Biszipped.zip 10993K

[st39422@dios8:/home/st39422]#

Contents of the created tarball: AB.tar

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

[st39422@dios8:/home/st39422]#

Updating a file(fileABC.tar) to the existing tar archive(AB.tar):

[st39422@dios8:/home/st39422]#tar -uvf  AB.tar  fileABC.tar

a fileABC.tar 8K

[st39422@dios8:/home/st39422]#

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

[st39422@dios8:/home/st39422]#

If you try to update the already available file in the archive, it will be added at the end of the archive; provided the file is modified. Otherwise it will be ignored.

[st39422@dios8:/home/st39422]#tar -uvf AB.tar fileABC.tar

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

[st39422@dios8:/home/st39422]#

Replace an existing file will always add the mentioned file at the end of the archive:

[st39422@dios8:/home/st39422]#tar -rvf AB.tar fileABC.tar

a fileABC.tar 8K

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

[st39422@dios8:/home/st39422]#

Replacing multiple files:

[st39422@dios8:/home/st39422]#tar -rvf AB.tar fileABC.tar fileABC.tar

a fileABC.tar 8K

a fileABC.tar 8K

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

[st39422@dios8:/home/st39422]#

Updating multiple files:

[st39422@dios8:/home/st39422]#tar -uvf AB.tar fileA fileB

a fileA 1K

a fileB 1K

[st39422@dios8:/home/st39422]#tar -tvf AB.tar

-rw-r--r-- 48153/63002 7486342 Aug  8 14:19 2012 Aiszipped.zip

-rw-r--r-- 48153/63002 11256018 Aug  8 14:19 2012 Biszipped.zip

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002   8192 Aug  6 12:55 2012 fileABC.tar

-rw-r--r-- 48153/63002    227 Aug  6 12:42 2012 fileA

-rw-r--r-- 48153/63002    227 Aug  6 12:43 2012 fileB

How to pass large number of files as an argument for tar archive creation?

Question: How to pass large number of files as an argument for tar archive creation?

Answer: Using the option ‘I’  

From Solaris Man page:

-I include-file   Opens include-file containing a list of  files,  one per line, and treats

                        it  as   if   each   file   appeared separately  on  the command line. Be

                        careful of  trailing  white  spaces. Also beware of leading white spaces,

                        since, for each line in the included file,  the  entire  line (apart from

                        the newline) will be used  to  match against  the initial string of files

                         to  include

SYNTAX:  tar –cvf  archive.tar  -I  filename 

archive.tar -> your desired archive name

filename ->  pass the file name which has list of files to be archived

Example:

Listing the available files:

[st39422@dios8:/home/st39422]#ls -ltr

total 64

-rw-r--r--   1 st39422  users        227 Aug  6 12:42 fileA

-rw-r--r--   1 st39422  users        227 Aug  6 12:43 fileB

-rw-r--r--   1 st39422  users         19 Aug  6 12:47 fileD

-rw-r--r--   1 st39422  users         19 Aug  6 12:49 fileC

Putting filenames in a file and checking the content:

[st39422@dios8:/home/st39422]#cat > files_to_be_archived

fileA

fileB

fileC

fileD

[st39422@dios8:/home/st39422]#cat files_to_be_archived

fileA

fileB

fileC

filed

Creating a tar archive:

[st39422@dios8:/home/st39422]#tar -cvf multiple_files.tar  -I files_to_be_archived

a fileA 1K

a fileB 1K

a fileC 1K

a fileD 1K

Listing tar file contents:

[st39422@dios8:/home/st39422]#tar -tvf multiple_files.tar

tar: blocksize = 10

-rw-r--r-- 48153/63002    227 Aug  6 12:42 2012 fileA

-rw-r--r-- 48153/63002    227 Aug  6 12:43 2012 fileB

-rw-r--r-- 48153/63002     19 Aug  6 12:49 2012 fileC

-rw-r--r-- 48153/63002     19 Aug  6 12:47 2012 fileD

[st39422@dios8:/home/st39422]#

NOTE:  Depending on the type and version of tar utility, option needs to be used ( -I or –L  eg: tar -cvf abc.tar -L jskfile or tar -cvf xyz.tar -I jskfile )

How to extract the desired file/directory from a tar archive in Unix or Linux or Solaris

Question: To extract the desired file/directory from a tarball

Answer:  Pass the desired file/directory as an extra argument to the normal tar extraction command

Syntax:   tar –xvf  filename.tar  desiredfilename/dirname

Example: To extract a file which is under two directories

1.      First we need to know the location of the file in the tarball  ( tar –tvf filename.tar  | grep filename)

2.      Secondly we need to apply that location as an additional argument  ( tar –xvf filename.tar  “output of last command” )

Now the command part,

[vjsujay@cheetah:/home/vjsujay]#tar -tvf abcd.tar | grep FileD

tar: blocksize = 15

-rw-r--r-- 48153/63002     14 Aug  2 12:41 2012 ./c/d/FileD

[vjsujay@cheetah:/home/vjsujay]#tar -xvf abcd.tar ./c/d/FileD

tar: blocksize = 15

x ./c/d/FileD, 14 bytes, 1 tape blocks

NOTE: If similar file already exist in the same location, then please move the tarball to different location and extract it to avoid the overwritten of the file

How to find the default shell in UNIX or Linux or Solaris

Question: Default shell of the logged in User

Answer: There are many ways to find the default shell.

a)      By checking the last column in the /etc/passwd file  ( grep –i username /etc/passwd )

Eg:  [vjsujay@cheetah:/home/vjsujay]#grep -i vjsujay /etc/passwd

       vjsujay:x:48153:63002:Sujay-kumar:/home/vjsujay:/bin/ksh

b)      By displaying the value of global environment variable SHELL  ( echo $SHELL )

Eg: [vjsujay@cheetah:/home/vjsujay]#echo $SHELL

/bin/ksh

NOTE: This will give correct default shell name as output as long as your current shell is your default shell

c)      By using the command echo $0

Eg: [vjsujay@cheetah:/home/st39422]#echo $0

-ksh

       

What is the flow in UNIX or UNIX like operating system for commands execution?

As soon as we press the enter key after the command, the below sequence will be followed.

1.  Check alias and then execute the command(shell-built-in or external command) accordingly
2.  Shell built-in command
3.  External command

Note 1: If command is executed with absolute path then external command or script will run. Else above sequence will be followed.

Note 2: If PATH value is empty, then shell will presume that the command is available in the current directory and hence it will try to run it from current directory.

Why we shouldn't give 777 to any directory in UNIX or LINUX?

Giving 777 to any directory in UNIX or Linux or UNIX based Operating System is a potential security risk. Because if a directory contains 777 permission, then any user can get inside the directory and remove other users files or directories. At times, we may need to permit all users to get in to the same directory and also need to allow them to create files and directories. In that case, we have to set 'sticky' bit for the particular directory to avoid the issue of removal of other users files intentionally.

How to find RAM size, CPU speed and CPU count in Solaris Sparc System

1.)Question: How to find the number of CPU, CPU Speed and RAM size?

Ans: prtdiag

Command Name: prtdiag

Purpose: To display the system diagnostics information

Ex:

[st39422@dios8:/home/st39422]#/usr/sbin/prtdiag -v

System Configuration: Sun Microsystems  sun4u Sun Ultra 45 Workstation

System clock frequency: 200 MHZ

Memory size: 2GB

==================================== CPUs ====================================

               E$          CPU                    CPU

CPU  Freq      Size        Implementation         Mask    Status      Location

---  --------  ----------  ---------------------  -----   ------      --------

0    1600 MHz  1MB         SUNW,UltraSPARC-IIIi    3.4    on-line     MB/0

============================ Memory Configuration ============================

Segment Table:

-----------------------------------------------------------------------

Base Address       Size       Interleave Factor  Contains

-----------------------------------------------------------------------

0x0                2GB               4           BankIDs 0,1,2,3

[st39422@dios8:/home/st39422]#

2.) Question: How to find the number of CPU?

Ans: psrinfo

Command Name: psrinfo

Purpose: To display information about processors

Ex:

[st39422@dios8:/home/st39422]#psrinfo -p

1

3.) Question: How to find the memory size(RAM)?

Ans: prtconf

Command Name: prtconf

Purpose: To print system configuration

Ex:

[st39422@dios8:/home/st39422]#prtconf -v | grep 'Memory'

Memory size: 2048 Megabytes

How to find empty files in UNIX?

There are multiple ways to find whether a file is empty or not. Please see few examples below,

volcano@volcano-laptop:~/shellscript$ ls -ltr | grep '\<0\>'
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:41 sujay
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:42 jsk
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:45 a
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:46 b
-rw-r--r-- 1 volcano volcano    0 2011-04-10 22:30 emptyfile

volcano@volcano-laptop:~/shellscript$ ls -ltr | awk ' $5==0 {print}'
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:41 sujay
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:42 jsk
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:45 a
-rw-r--r-- 1 volcano volcano    0 2011-03-12 15:46 b
-rw-r--r-- 1 volcano volcano    0 2011-04-10 22:30 emptyfile

volcano@volcano-laptop:~/shellscript$ for fname in `ls`;do if [ ! -s $fname ];then ls -l $fname;fi;done
-rw-r--r-- 1 volcano volcano 0 2011-03-12 15:45 a
-rw-r--r-- 1 volcano volcano 0 2011-03-12 15:46 b
-rw-r--r-- 1 volcano volcano 0 2011-04-10 22:30 emptyfile
-rw-r--r-- 1 volcano volcano 0 2011-03-12 15:42 jsk
-rw-r--r-- 1 volcano volcano 0 2011-03-12 15:41 sujay

volcano@volcano-laptop:~/shellscript$ find . -maxdepth 1 -size 0 -ls
 58438    0 -rw-r--r--   1 volcano  volcano         0 Mar 12 15:42 ./jsk
 58434    0 -rw-r--r--   1 volcano  volcano         0 Mar 12 15:46 ./b
 58437    0 -rw-r--r--   1 volcano  volcano         0 Mar 12 15:41 ./sujay
 58211    0 -rw-r--r--   1 volcano  volcano         0 Mar 12 15:45 ./a
 58234    0 -rw-r--r--   1 volcano  volcano         0 Apr 10 22:30 ./emptyfile

How to remove empty lines from a file in UNIX or Linx

volcano@volcano-laptop:~/shellscript/empty$ cat testempty
hi first line

above line is empty
hi dude

above line is empty
volcano@volcano-laptop:~/shellscript/empty$ sed '/^$/d' testempty > testwithoutempty
volcano@volcano-laptop:~/shellscript/empty$ cat testwithoutempty
hi first line
above line is empty
hi dude
above line is empty
volcano@volcano-laptop:~/shellscript/empty$

volcano@volcano-laptop:~/shellscript/empty$ grep -v '^$' testempty > without
volcano@volcano-laptop:~/shellscript/empty$ cat without
hi first line
above line is empty
hi dude
above line is empty

One exception case is available for empty line removal. That is line will be empty but it will have space or tab characters. To handle that, we can use the below command format.


grep -v '^[]*]$'  oldfile > newfile

volcano@volcano-laptop:~/shellscript/empty$ cat test
hi first line

above line is empty
hi dude

above line is empty
   
volcano@volcano-laptop:~/shellscript/empty$ grep -v '^[         ]*$' test > newtest
volcano@volcano-laptop:~/shellscript/empty$ cat newtest
hi first line
above line is empty
hi dude
above line is empty
volcano@volcano-laptop:~/shellscript/empty$

volcano@volcano-laptop:~/shellscript/empty$ sed '/^$/d' test
hi first line
above line is empty
hi dude
above line is empty
   
volcano@volcano-laptop:~/shellscript/empty$ sed '/^[    ]*$/d' test
hi first line
above line is empty
hi dude
above line is empty
volcano@volcano-laptop:~/shellscript/empty$

How to remove CONTROL-M characters in UNIX or Linux

Control-m characters will get appended to a file when a file is transferred from windows to UNIX machine. There are multiple ways it can be removed.


Using vi editor:
:%s/^M//g

Using col command:
cat filename | col -b > newfilename

Using sed command:
sed 's/^M//g' filename > newfilename

Using dos2unix comand:
dos2unix filename newfilename

Examples:

volcano@volcano-laptop:~/shellscript/ctrl$ cat -v jsk
hi^M
jsk^M
volcano@volcano-laptop:~/shellscript/ctrl$ cat jsk | col -b > jsk.new
volcano@volcano-laptop:~/shellscript/ctrl$ cat -v jsk.new
hi
jsk
volcano@volcano-laptop:~/shellscript/ctrl$ sed 's/^M//g' jsk > jsk.new2
volcano@volcano-laptop:~/shellscript/ctrl$ cat -v jsk.new2
hi
jsk

Note: Hold the control key and then press v and m to get the control-m character

How to remove files starting with - minus in the filename

There might be several ways to remove files starting with first character as - minus. But i am providing 3 solutions below.

1. $ rm ./-filename

2. $ rm -- -filename

3. Find the inode number by using ls -i and then use the below command
find . -inum 45678 -exec rm {} \;

Difference between Unix Internal & External Commands

Internal Unix commands are built with the shell and hence it will run in the same shell.
eg: cd

External Unix commands will start a new shell and then it gets executed
eg: ls

Note: If you execute a shell script, it will create or fork a new shell and then execute the commands present in the script file. You can also execute the shell script in the same shell by using source or . infront of the shell script.

eg:
sujay@laptop:~/scripts$ cat test.sh
cd /
echo "Current dir is `pwd`"

sujay@laptop:~/scripts$ test.sh
Current dir is /
sujay@laptop:~/scripts$ pwd
/home/sujay/scripts
sujay@laptop:~/scripts$ source test.sh
Current dir is /
sujay@laptop:/$ pwd
/

How to run a unix shell script from any directory

To run a script from anywhere inside UNIX directory, you need to include the script absolute directory in the PATH variable. After that without using the pathname we can execute the script successfully.

eg:
In .profile, update PATH=$PATH:/home/sujay/scripts and source the .profile

Script Loc: /home/sujay/scripts/
Script Name; anywhere

sujay@laptop:~$ anywhere
++ pwd
+ echo 'Executed from /home/sujay'
Executed from /home/sujay

Order of execution for /etc/profile .bash_profile .bash_login .profile /etc/bash.bashrc .bashrc

If interactive login-shell or non-interactive login shell with --Login option is started, it will start reading & executing in the order /etc/profile, .bash_profile, .bash_login and finally .profile

If interactive shell, that is a non-login shell is started, it will start reading & executing in the order /etc/bash.bashrc, .bashrc

Difference between .profile and .bashrc

.profile will be read, whenever login-shell is started

.bashrc will be read, whenever new interactive shell(not a login shell) is started

How to compress multiple files using tar and gzip

1. Put all the required filenames in a file

2. tar all the files

3. gzip the tar file

eg:

vjsujay@gmail.com$ ls *.html > filelist

vjsujay@gmail.com$ fname=filelist

vjsujay@gmail.com$ tar -cvf multihtml.tar -L $fname

vjsujay@gmail.com$ gzip multihtml.tar

Final file will be multihtml.tar.gz

To display only the user directories in Unix or Linux

vjsujay@home$ ls -lA "pipeline symbol" grep '^d'
drwxr-s--- 2 n0160429 ccipadm 512 Jul 21 00:17 .temp
drwxr-s--- 2 n0160429 ccipadm 512 Mar 15 04:58 cal
drwxr-s--- 2 n0160429 ccipadm 512 May 06 04:50 dump
drwxr-s--- 2 n0160429 ccipadm 512 May 05 23:14 script
drwxr-s--- 2 n0160429 ccipadm 512 Jul 18 12:28 temp

Note: If you use ls -la means, you will get . (dot) and .. (dot dot) directory also.

Difference between single square and double square brackets in conditional check in shell scripting

1. [ conditional check ] -> Variables used in the conditional check should have value, otherwise exception will be thrown during the execution.

2. [[ cond check ]] -> Exception will not thrown, even if variable don't have value or not received any value during the execution.

So, it is advisable to use single square bracket always to ensure whether we are receiving the value and doing the conditional checking.

example:
echo "Enter your name: "
read NAME
if [[ $NAME == "sujay" ]]
then
echo Your name is $NAME
else
echo Your name is $NAME from else part
fi

$ ksh doublesquare.sh
Enter your name:
sujay
Your name is sujay

$ ksh doublesquare.sh
Enter your name:

Your name is from else part

Note: If double square bracket is replaced with single: if [ $NAME == "sujay" ]
$ ksh singlesquare.sh
Enter your name:
sujay
Your name is sujay
$ ksh singlesquare.sh
Enter your name:

singlesquare.sh[4]: test: 0403-004 Specify a parameter with this command.
Your name is from else part

Different type of Command Substitution in Shell Scripting

In two ways we can do the command substitution.
1.) Using backquote: ``
2. Using dollar sign and parenthesis: $()
eg:
vjsujay@home $ echo My system name is `uname -n`
vjsujay@home $ echo My system name is $(uname -n)

To find last day of any month & year using unix command

How to keep track of your Unix/Linux command execution and its output

By using "script" command, you can keep track of Executed Commands and its output.

Definition: The script command will keep a transcript(written record) of everything you say to the computer and everything that the computer responds to you.

Syntax: script [capturefilename]

*) To start the script command
eg: vjsujay$ script cmdlog

Note: cmdlog will be created in the current dir and also if you are not specifying the filename means, it will create a default filename 'typescript'

*) To stop capturing or script command,
eg: vjsujay$ exit

Different ways of running a Shell Script

1. Executing the Shell Script file as a command in the Shell Prompt
vjsujay@linuxdemon$sample.sh

2. Executing the Shell Script file using specified Shell
vjsujay@linuxdemon$bash sample.sh

3. Executing the Shell Script file in the current Shell
vjsujay@linuxdemon$source sample.sh
or
vjsujay@linuxdemon$. sample.sh

4. Executing the Shell Script file using exec command
vjsujay@linuxdemon$ exec sample.sh

Copying longfilenames without retyping

$ ls -l thisismytestfile
-rw-r--r-- 1 Ajay None 13 Apr 17 03:22 thisismytestfile

Ajay@intel ~
$ cp thisismytestfile{,.bk}

Ajay@intel ~
$ ls -l thisismytest*
-rw-r--r-- 1 Ajay None 13 Apr 17 03:22 thisismytestfile
-rw-r--r-- 1 Ajay None 13 Apr 17 03:26 thisismytestfile.bk

How to Truncate a file in Unix/Linux

:>filename

If the filename already exists,the file will be truncated to ZERO byte file else a new file with ZERO byte will be created.

Example:

[vjsujay@phenix vjsujay]$ ls -l jsk
-rw-r----- 1 vjsujay free 46 Jun 25 20:14 jsk

[vjsujay@phenix vjsujay]$ : > jsk

[vjsujay@phenix vjsujay]$ ls -l jsk
-rw-r----- 1 vjsujay free 0 Jun 25 20:15 jsk

One more example with 3 different methods:

volcano@volcano-laptop:~/test/trunc$ ls -ltr
total 12
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:56 rado
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:57 radoo
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:57 radooo
volcano@volcano-laptop:~/test/trunc$ > rado
volcano@volcano-laptop:~/test/trunc$ :>radoo
volcano@volcano-laptop:~/test/trunc$ true > radooo
volcano@volcano-laptop:~/test/trunc$ ls -ltr
total 0
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 rado
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 radoo
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 radooo

Commenting Multiple lines in a shell script

By using anonymous here document, we can comment multiple lines in a shell script for debugging purposes.

eg:

: << COMMENT
echo "Not in the Scope of debugging/execution"
a=5
b=3
let c=a+b
echo $c
COMMENT

The statements in between the anonymous here document will not be executed.

Length of a string in Linux

The command syntax is ${#string}

Example:
linuxdemon$lindem="linux demon"
linuxdemon$echo ${#lindem}
11

Explanation:
1.Assigning the string linux demon to the variable lindem.
2.Determining and printing the length of the string.

FTP Automation using Shell script

I am going to give the code in shell script for ftp automation.

ftp -n servername/serverIP << FTP_AUTO
user giveusername givepassword

Any ftp command you can give here

bye
FTP_AUTO

Explanation:
1. -n is used to restrict the ftp from attempting auto login.
2. << here document concept applied here and hence the tag is FTP_AUTO
3. user is the ftp command
4. You can give any ftp command after the user command to do your job.
5.End the here document with the same tag FTP_AUTO

How to mount WIN partition in Linux?

Temporary Mounting: After the reboot of your system, you need to again execute the mount command to mount the win partition in Linux.

1.You need to create mount point(directory) for each win partition(drives) inside the /mnt directory.
eg: mkdir /mnt/winc (You can give any name instead of winc)

2. By using the mount command, we can now mount the windows partition
eg: mount -t vfat /dev/hda1 /mnt/winc (In linux, first partition is called as hda1)

3. Now get inside the /mnt/winc directory and check the files.You will be able to see your files from C drive.
eg: cd /mnt/winc

Permanent Mounting: To do the permanent mounting, you need to follow these steps below.

1.Create mount points (mkdir /mnt/winc)

2.Edit the /etc/fstab file using any text editor like vi and insert the mount point and file system details at the end of the file with the proper spacing as previous lines.
eg: /dev/hda1 /mnt/winc vfat

3. After the reboot of your system, you will be able to access all C drive files.

How to rename group of files?

I am giving a simple shell script, for renaming a group of files in the current directory.In the script, i have renamed all .jsk files to .txt files.

for filename in *.jsk
do
mv $filename `basename $filename jsk`txt
done

Explanation:
1.In the for statement, i am finding out all the .jsk extension files.
2.In the mv statement, i am using basename command to strip the jsk extension.