NextGen4IT: Unix Commands

Unix/Linux Commands description


Command		Description
Ls		link file or directory
Psd		for background running jobs
Cd		change directory
Clear		clear screen
diff,comm,cmp		file compare
Cp		file copy
Ctl-C		break (signal)
Ctl-D		EOF (end-of-file)
rm–rf		delete directory recursively
Rm		delete file(s)
Exit		exit current process
Grep		find strings in files
Mkdir		make directory
More		text file paging filter
$PATH		path to executables
Mv		rename (move)
Rmdir		remove directory
Sort		sort file
Date		display system time
Cat		output file to stdout
Scp		secure file copy
Gzip		Compress named file(s)
gunzip		decompress named file(s)
man		Help manual
mv		Move or rename files or directories
Cal		Display a calendar
cat		Concatenate and print (display) the content of files
chmod		Change access permissions
crontab		Schedule a command to run at a later time
echo		Display message on screen •
egrep		Search file(s) for lines that match an extended expression
exit		Exit the shell
fgrep		Search file(s) for lines that match a fixed string
free		Display memory usage
grep		Search file(s) for lines that match a given pattern
hostname		Print or set system name
help		Display help for a built-in command
jobs		List active jobs
kill		Stop a process from running
killall		Kill processes by name
less		Display output one screen at a time
logout		Exit a login shell
nohup		Run a command immune to hang-ups
passwd		Modify a user password
Pwd		Print Working Directory
Sed		Stream Editor
Su		Substitute user identity
sudosu		Execute a command as another user
tail		Output the last part of file
tar		Tape ARchiver
time		Measure Program running time
vi		Text Editor
vmstat		Report virtual memory statistics
Wc		Print byte, word, and line counts
who		Print all usernames currently logged in
whoami		Print the current user id and name (`id -un')
export		Set an environment variable
.		Run a command script in the current shell
!!		Run the last command again
###		Comment / Remark

How to Use Unix Commands

Command	Example	Description
Ls	Ls	Lists files in current directory
	ls –alF	List in long format
Cd	cd tempdir	Change directory to tempdir
	cd ..	Move back one directory
	cd ~dhyatt/web-docs	Move into dhyatt's web-docs directory
Mkdir	mkdir graphics	Make a directory called graphics
Rmdir	rmdiremptydir	Remove directory (must be empty)
Cp	cp file1 web-docs	Copy file into directory
	cp file1 file1.bak	Make backup of file1
Rm	rm file1.bak	Remove or delete file
	rm *.tmp	Remove all file
Mv	mv old.html new.html	Move or rename files
More	more index.html	Look at file, one page at a time
Man	man ls	Online manual (help) about command
grep <str><files>	grep "bad word" *	Find which files contain a certain word
chmod<opt><file>	chmod 644 *.html	Change file permissions read only
	chmod 755 file.exe	Change file permissions to executable
Passwd	Passwd	Change passwd
ps<opt>	ps aux	List all running processes by #ID
	ps aux \| grep dhyatt	List process #ID's running by dhyatt
kill <opt><ID>	kill -9 8453	Kill process with ID #8453
gcc (g++) <source>	gccfile.c -o file	Compile a program written in C
	g++ fil2.cpp -o fil2	Compile a program written in C++
gzip<file>	gzipbigfile	Compress file
	gunzip bigfile.gz	Uncompress file
Mail	mail me@tjhsst.edu < file1	Send file1 by email to someone
(pine)	Pine	Read mail using pine
telnet <host>	telnet vortex.tjhsst.edu	Open a connection to vortex
ssh<host>	ssh -l dhyatt jazz.tjhsst.edu	Open a secure connection to jazz as user dhyatt
ftp <host>	ftp station1.tjhsst.edu	Upload or Download files to station1
ncftp<host/directory>	ncftp metalab.unc.edu	Connect to archives at UNC
Who	Who	Lists who is logged on your machine
History	History	Lists commands you've done recently
Date	Date	Print out current date
cal<mo><yr>	cal 9 2000	Print calendar for September 2000
Xcalc	xcalc&	Calculator ("background" process)
ispell<fname>	ispell file1	Spell check file1
latex <fname>	latex file.tex	Run LaTeX, a scientific document tool
Df	Df	See how much free disk space
Du	du -b subdir	Estimate disk usage of directory in Bytes
Alias	alias lls="ls -alF"	Create new command "lls" for long format of ls
Tar	tar -cf subdir.tar subdir	Create an archive called subdir.tar of a directory
	tar -xvf subdir.tar	Extract files from an archive file
logout (exit)	logout or exit	How to quit a UNIX shell.

Unix/Linux Commands Examples

Linux Commands:

1. tar command examples

Create a new tar archive.

$ tar cvf archive_name.tar dirname/

Extract from an existing tar archive.

$ tar xvf archive_name.tar

View an existing tar archive.

$ tar tvf archive_name.tar

2. grep command examples

Search for a given string in a file (case in-sensitive search).

$ grep -i "the" demo_file

Print the matched line, along with the 3 lines after it.

$ grep -A 3 -i "example" demo_text

Search for a given string in all files recursively

$ grep -r "ramesh" *

3. find command examples

Find files using file-name ( case in-sensitve find)

# find -iname "demo.c"

Execute commands on files found by the find command

$ find -iname "MyCProgram.c" -exec md5sum {} \;

Find all empty files in home directory

# find ~ -empty

4. ssh command examples

ssh -l jsmith remotehost.example.com

Debug ssh client

ssh -v -l jsmith remotehost.example.com

Display ssh client version

$ ssh -V

OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003

5. sed command examples

When you copy a DOS file to Unix, you could find \r\n in the end of each line. This example converts the DOS file format to Unix file format using sed command.

$sed 's/.$//' filename

Print file content in reverse order

$ sed -n '1!G;h;$p' thegeekstuff.txt

Add line number for all non-empty-lines in a file

$ sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'

6. awk command examples

Remove duplicate lines using awk

$ awk '!($0 in array) { array[$0]; print }' temp

Print all lines from /etc/passwd that has the same uid and gid

$awk -F ':' '$3==$4' passwd.txt

Print only specific field from a file.

$ awk '{print $2,$5;}' employee.txt

7. vim command examples

Go to the 143rd line of file

$ vim +143 filename.txt

Go to the first match of the specified

$ vim +/search-term filename.txt

Open the file in read only mode.

$ vim -R /etc/passwd

8. diff command examples

Ignore white space while comparing.

# diff -w name_list.txt name_list_new.txt

2c2,3

< John Doe --- > John M Doe

> Jason Bourne

9. sort command examples

Sort a file in ascending order

$ sort names.txt

Sort a file in descending order

$ sort -r names.txt

Sort passwd file by 3rd field.

$ sort -t: -k 3n /etc/passwd | more

10. export command examples

To view oracle related environment variables.

$ export | grep ORACLE

declare -x ORACLE_BASE="/u01/app/oracle"

declare -x ORACLE_HOME="/u01/app/oracle/product/10.2.0"

declare -x ORACLE_SID="med"

declare -x ORACLE_TERM="xterm"

To export an environment variable:

$ export ORACLE_HOME=/u01/app/oracle/product/10.2.0

11. xargs command examples

Copy all images to external hard-drive

# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory

Search all jpg images in the system and archive it.

# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz

Download all the URLs mentioned in the url-list.txt file

# cat url-list.txt | xargs wget –c

12. ls command examples

Display filesize in human readable format (e.g. KB, MB etc.,)

$ ls -lh

-rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz

Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr

$ ls -ltr

Visual Classification of Files With Special Characters Using ls -F

$ ls -F

13. pwd command

pwd is Print working directory. What else can be said about the good old pwd who has been printing the current directory name for ages.

14. cd command examples

Use “cd -” to toggle between the last two directories

Use “shopt -s cdspell” to automatically correct mistyped directory names on cd

15. gzip command examples

To create a *.gz compressed file:

$ gzip test.txt

To uncompress a *.gz file:

$ gzip -d test.txt.gz

Display compression ratio of the compressed file using gzip -l

$ gzip -l *.gz

compressed uncompressed ratio uncompressed_name

23709 97975 75.8% asp-patch-rpms.txt

16. bzip2 command examples

To create a *.bz2 compressed file:

$ bzip2 test.txt

To uncompress a *.bz2 file:

bzip2 -d test.txt.bz2

17. gunzip command examples

To extract a *.zip compressed file:

$ unzip test.zip

View the contents of *.zip file (Without unzipping it):

$ unzip -l jasper.zip

Archive: jasper.zip

Length Date Time Name

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

40995 11-30-98 23:50 META-INF/MANIFEST.MF

32169 08-25-98 21:07 classes_

15964 08-25-98 21:07 classes_names

10542 08-25-98 21:07 classes_ncomp

18. shutdown command examples

Shutdown the system and turn the power off immediately.

# shutdown -h now

Shutdown the system after 10 minutes.

# shutdown -h +10

Reboot the system using shutdown command.

# shutdown -r now

Force the filesystem check during reboot.

# shutdown -Fr now

19. ftp command examples

Both ftp and secure ftp (sftp) has similar commands. To connect to a remote server and download multiple files, do the following.

$ ftp IP/hostname

ftp> mget *.html

To view the file names located on the remote server before downloading, mls ftp command as shown below.

ftp> mls *.html -

/ftptest/features.html

/ftptest/index.html

/ftptest/othertools.html

/ftptest/samplereport.html

/ftptest/usage.html

20. crontab command examples

View crontab entry for a specific user

# crontab -u john -l

Schedule a cron job every 10 minutes.

*/10 * * * * /home/ramesh/check-disk-space

21. service command examples

Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the

/etc/init.d/ directory with their full path, you can use the service command.

Check the status of a service:

# service ssh status

Check the steatus of all the services.

service --status-all

Restart a service.

# service ssh restart

22. ps command examples

ps command is used to display information about the processes that are running in the system.

While there are lot of arguments that could be passed to a ps command, following are some of the common ones.

To view current running processes.

$ ps -ef | more

To view current running processes in a tree structure. H option stands for process hierarchy.

$ ps -efH | more

25. df command examples

Displays the file system disk space usage. By default df -k displays output in bytes.

$ df -k

Filesystem 1K-blocks Used Available Use% Mounted on

/dev/sda1 29530400 3233104 24797232 12% /

/dev/sda2 120367992 50171596 64082060 44% /home

df -h displays output in human readable form. i.e size will be displayed in GB’s.

ramesh@ramesh-laptop:~$ df -h

Filesystem Size Used Avail Use% Mounted on

/dev/sda1 29G 3.1G 24G 12% /

/dev/sda2 115G 48G 62G 44% /home

Use -T option to display what type of file system.

ramesh@ramesh-laptop:~$ df -T

Filesystem Type 1K-blocks Used Available Use% Mounted on

/dev/sda1 ext4 29530400 3233120 24797216 12% /

/dev/sda2 ext4 120367992 50171596 64082060 44% /home

26. kill command examples

Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process.

$ ps -ef | grep vim

ramesh 7243 7222 9 22:43 pts/2 00:00:00 vim

$ kill -9 7243

27. rm command examples

Get confirmation before removing the file.

$ rm -i filename.txt

It is very useful while giving shell metacharacters in the file name argument.

Print the filename and get confirmation before removing the file.

$ rm -i file*

Following example recursively removes all files and directories under the example directory. This also removes the example directory itself.

$ rm -r example

28. cp command examples

Copy file1 to file2 preserving the mode, ownership and timestamp.

$ cp -p file1 file2

Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it.

$ cp -i file1 file2

29. mv command examples

Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it.

$ mv -i file1 file2

Note: mv -f is just the opposite, which will overwrite file2 without prompting.

mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument.

$ mv -v file1 file2

30. cat command examples

You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout.

$ cat file1 file2

While displaying the file, following cat -n command will prepend the line number to each line of the output.

$ cat -n /etc/logrotate.conf

1 /var/log/btmp {

2 missingok

3 monthly

4 create 0660 root utmp

5 rotate 1

6 }

31. mount command examples

To mount a file system, you should first create a directory and mount it as shown below.

# mkdir /u01

# mount /dev/sdb1 /u01

You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted.

/dev/sdb1 /u01 ext2 defaults 0 2

32. chmod command examples

chmod command is used to change the permissions for a file or directory.

Give full access to user and group (i.e read, write and execute ) on a specific file.

$ chmod ug+rwx file.txt

Revoke all access for the group (i.e read, write and execute ) on a specific file.

$ chmod g-rwx file.txt

Apply the file permissions recursively to all the files in the sub-directories.

$ chmod -R ug+rwx file.txt

33. chown command examples

chown command is used to change the owner and group of a file. \

To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.

$ chown oracle:dba dbora.sh

Use -R to change the ownership recursively.

$ chown -R oracle:dba /home/oracle

34. passwd command examples

Change your password from command line using passwd. This will prompt for the old password followed by the new password.

$ passwd

Super user can use passwd command to reset others password. This will not prompt for current password of the user.

# passwd USERNAME

Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.

# passwd -d USERNAME

35. mkdir command examples

Following example creates a directory called temp under your home directory.

$ mkdir ~/temp

Create nested directories using one mkdir command. If any of these directories exist already, it will not display any error. If any of these directories doesn’t exist, it will create them.

$ mkdir -p dir1/dir2/dir3/dir4/

36. ifconfig command examples

Use ifconfig command to view or configure a network interface on the Linux system.

View all the interfaces along with status.

$ ifconfig -a

Start or stop a specific interface using up and down command as shown below.

$ ifconfig eth0 up

$ ifconfig eth0 down

37. uname command examples

Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number,

Processor type, etc.,

Sample uname output from a Ubuntu laptop is shown below.

$ uname -a

Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux

38. whereis command examples

When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command.

$ whereis ls

ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz

When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available.

$ whereis -u -B /tmp -f lsmk

lsmk: /tmp/lsmk

39. whatis command examples

Whatis command displays a single line description about a command.

$ whatis ls

ls (1) - list directory contents

$ whatis ifconfig

ifconfig (8) - configure a network interface

40. locate command examples

Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb.

The example below shows all files in the system that contains the word crontab in it.

$ locate crontab

/etc/anacrontab

/etc/crontab

/usr/bin/crontab

/usr/share/doc/cron/examples/crontab2english.pl.gz

/usr/share/man/man1/crontab.1.gz

/usr/share/man/man5/anacrontab.5.gz

/usr/share/man/man5/crontab.5.gz

/usr/share/vim/vim72/syntax/crontab.vim

41. man command examples

Display the man page of a specific command.

$ man crontab

When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below.

$ man SECTION-NUMBER commandname

Following 8 sections are available in the man page.

General commands

System calls

C library functions

Special files (usually devices, those found in /dev) and drivers

File formats and conventions

Games and screensavers

Miscellaneous

System administration commands and daemons

For example, when you do whatis crontab, you’ll notice that crontab has two man pages (section 1 and section 5). To view section 5 of crontab man page, do the following.

$ whatis crontab

crontab (1) - maintain crontab files for individual users (V3)

crontab (5) - tables for driving cron

$ man 5 crontab

42. tail command examples

Print the last 10 lines of a file by default.

$ tail filename.txt

Print N number of lines from the file named filename.txt

$ tail -n N filename.txt

View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C.

$ tail -f log-file

43. less command examples

less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening.

$ less huge-log-file.log

One you open a file using less command, following two keys are very helpful.

CTRL+F – forward one window

CTRL+B – backward one window

44. su command examples

Switch to a different user account using su command. Super user can switch to any other user without entering their password.

$ su - USERNAME

Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john’s account.

[john@dev-server]$ su - raj

[john@dev-server]$

$ su -s 'SHELLNAME' USERNAME

45. mysql command examples

mysql is probably the most widely used open source database on Linux. Even if you don’t run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server.

To connect to a remote mysql database. This will prompt for a password.

$ mysql -u root -p -h 192.168.1.2

To connect to a local mysql database.

$ mysql -u root -p

If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space).

49. date command examples

Set the system date:

# date -s "01/31/2010 23:59:53"

Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.

# hwclock –systohc

# hwclock --systohc –utc

50 banner command examples

Banner command give design of names in the form of # symbols

~ $ banner suresh

#### # # ##### ###### #### # #

# # # # # # # # #

#### # # # # ##### #### ######

# # # ##### # # # #

# # # # # # # # # # #

#### #### # # ###### #### # #

wc:

wc filename

X Y Z filename

X – Number of lines

Y – Number of words

Z – Number of bytes

filename – name of the file

EX:

wc demofile.txt

36 104 570 demofile.txt

51 Symbolic or soft Links

Symbolic links, sometimes called "soft" links, are different than "hard" links. Instead of linking to the data of a file, they link to another link. So in the example above, file2.txtpoints to the link file1.txt, which in turn points to the data of the file.

This has several potential benefits. For one thing, symbolic links (also called "symlinks" for short) can link to directories. Also, symbolic links can cross file system boundaries, so a symbolic link to data on one drive or partition can exist on another drive or partition.

You should also be aware that, unlike hard links, removing the file (or directory) that a symlink points to will break the link. So if we create file1.txt:

echo "This is a file." > file1.txt

...and create a symbolic link to it:

ln -s file1.txt file2.txt

...we can cat either one of these to see the contents:

cat file1.txt

This is a file.

cat file2.txt

This is a file.

...but if we remove file1.txt:

rm file1.txt

...we can no longer access the data it contained with our symlink:

cat file2.txt

cat: file2.txt: No such file or directory

53 hard link

echo "This is a file." > file1.txt

...and create a hard link to it:

ln file1.txt file2.txt

...we can cat either one of these to see the contents:

cat file1.txt

This is a file.

cat file2.txt

This is a file.

...but if we remove file1.txt:

rm file1.txt

...we can access the data it contained with our hardlink:

cat file2.txt

This is a file.

53.unlink

Used to remove the soft link or hard link

[/u03/appl/farbat1/suresh]$ ls -alrt

total 10

drwxr-xr-x 23 farbat1 arboradm 3072 Sep 28 12:06 ..

drwxrwxr-x 2 farbat1 arboradm 96 Sep 28 12:06 .

-rw-rw-r-- 2 farbat1 arboradm 47 Sep 28 12:07 file2.txt

-rw-rw-r-- 2 farbat1 arboradm 47 Sep 28 12:07 file1.txt

[/u03/appl/farbat1/suresh]$ unlink file2.txt

[/u03/appl/farbat1/suresh]$ ls -alrt

total 8

drwxr-xr-x 23 farbat1 arboradm 3072 Sep 28 12:06 ..

-rw-rw-r-- 1 farbat1 arboradm 47 Sep 28 12:07 file1.txt

drwxrwxr-x 2 farbat1 arboradm 96 Sep 28 12:13 .

[/u03/appl/farbat1/suresh]$

53 Tr command Examples:

1.
Convert lower case letters to upper case

The following tr command translates the lower case letters to capital letters in the give string:

>echo "linux dedicated server" | tr "[:lower:]" "[:upper:]"

LINUX DEDICATED SERVER

>echo "linux dedicated server" | tr "[a-z]" "[A-Z]"

LINUX DEDICATED SERVER

2.
Transform upper case letters to lower case.

Similar to the above example, you can translate the uppercase letters to small letters.

> echo "UNIX DEDICATED SERVER" | tr "[:upper:]" "[:lower:]"

unix dedicated server

> echo "UNIX DEDICATED SERVER" | tr "[A-Z]" "[a-z]"

unix dedicated server

3.
Replace non-matching characters.

The -c option is used to replace the non-matching characters with another set of characters.

> echo "unix" | tr -c "u" "a"

uaaa

In the above example, except the character "c" other characters are replaced with "a"

4. Delete non-printable characters

The -d option can be used to delete characters. The following example deletes all the non-printable characters from a file.

>tr -cd "[:print:]" < filename

5. Squeezing characters

You can squeeze more than one occurrence of continuous characters with single occurrence. The following example squeezes two or more successive blank spaces into a single space.

>echo "linux server" | tr -s " "

linux server

Here you can replace the space character with any other character by specifying in set2.

> "linux server" | tr -s " " ","

linux,server

6.
Delete characters

The following example removes the word linux from the string.

> echo "linuxserver" | tr -d "linux"

server

54 tee examples

ls -1 *.txt | wc -l | tee count.txt

In the above example, the ls command lists all files in the current directory that have the filename extension .txt, one file per line; this output is piped to wc, which counts the lines and outputs the number; this output is piped to tee, which writes the output to the terminal, and writes the same information to the file count.txt. If count.txt already exists, it is overwritten.

55 NL

To provide sequence to the script.

cat list.txt

applesorangespotatoeslemonsgarlic

nl list.txt

1 apples 2 oranges 3 potatoes 4 lemons 5 garlic

In the above example, we use the cat command to display the contents of list.txt. Then we use nl to number each line and display the result to standard output.

56 pg examples

pg myfile.txt

Displays the first screenful of the contents of text file myfile.txt, and a prompt (":"). Pressing the RETURN key displays the next page, or any of the command listed above may be entered to otherwise navigate the file.

57 Paste Command Examples:

Create the following three files in your unix or linux servers to practice to practice the examples:

>cat file1

Unix

Linux

Windows

>cat file2

Dedicated server

Virtual server

>cat file3

Hosting

Machine

Operating system

1.
Merging files in parallel

By default, the paste command merges the files in parallel. The paste command writes corresponding lines from the files as a tab delimited on the terminal.

> paste file1 file2

Unix Dedicated server

Linux Virtual server

Windows

> paste file2 file1

Dedicated server Unix

Virtual server Linux

Windows

2.
Specifying the delimiter

Paste command uses the tab delimiter by default for merging the files. You can change the delimiter to any other character by using the -d option.

>paste -d"|" file1 file2

Unix|Dedicated server

Linux|Virtual server

Windows|

In the above example, pipe delimiter is specified

3. Merging files in sequentially.

You can merge the files in sequentially using the -s option. The paste command reads each file in sequentially. It reads all the lines from a single file and merges all these lines into a single line.

>paste -s file1 file2

Unix Linux Windows

Dedicated server Virtual server

The following example shows how to specify a delimiter for sequential merging of files:

> paste -s -d"," file1 file2

Unix,Linux,Windows

Dedicated server,Virtual server

4.
Specifying multiple delimiters.

Multiple delimiters come in handy when you want to merge more than two files with different delimiters. For example I want to merge file1, file2 with pipe delimiter and file2, file3 with comma delimiter. In this case multiple delimiters will be helpful.

>paste -d"|," file1 file2 file3

Unix|Dedicatedserver,Hosting

Linux|Virtualserver,Machine

Windows|,Operating system

5.
Combining N consecutive lines

The paste command can also be used to merge N consecutive lines from a file into a single line. The following example merges 2 consecutive lines into a single line

>cat file1 | paste - -

Unix Linux

Windows

57.CUT

Cut command in unix (or linux) is used to select sections of text from each line of files. You can use the cut command to select fields or columns from a line by specifying a delimiter or you can select a portion of text by specifying the range or characters. Basically the cut command slices a line and extracts the text.

$ cat test.txtcat command for file oriented operations.cp command for copy files or directories.ls command to list out files and directories with its attributes.

60. Select Column of Characters

To extract only a desired column from a file use -c option. The following example displays 2nd character from each line of a file test.txt

$ cut -c2 test.txtaps

As seen above, the characters a, p, s are the second character from each line of the test.txt file.

61. Select Column of Characters using Range

Range of characters can also be extracted from a file by specifying start and end position delimited with -. The following example extracts first 3 characters of each line from a file called test.txt

$ cut -c1-3 test.txtcatcpls

62. Select Column of Characters using either Start or End Position

Either start position or end position can be passed to cut command with -c option.

The following specifies only the start position before the ‘-‘. This example extracts from 3rd character to end of each line from test.txt file.

$ cut -c3- test.txtt command for file oriented operations.command for copy files or directories.command to list out files and directories with its attributes.

The following specifies only the end position after the ‘-‘. This example extracts 8 characters from the beginning of each line from test.txt file.

$ cut -c-8 test.txtcatcommcp commals comma

The entire line would get printed when you don’t specify a number before or after the ‘-‘ as shown below.

$ cut -c- test.txtcat command for file oriented operations.cp command for copy files or directories.ls command to list out files and directories with its attributes.

63. Select a Specific Field from a File

Instead of selecting x number of characters, if you like to extract a whole field, you can combine option -f and -d. The option -f specifies which field you want to extract, and the option -d specifies what is the field delimiter that is used in the input file.

The following example displays only first field of each lines from /etc/passwd file using the field delimiter : (colon). In this case, the 1st field is the username. The file

$ cut -d':' -f1 /etc/passwdrootdaemonbinsyssyncgamesbala

64. Select Multiple Fields from a File

You can also extract more than one fields from a file or stdout. Below example displays username and home directory of users who has the login shell as “/bin/bash”.

$ grep "/bin/bash" /etc/passwd | cut -d':' -f1,6root:/rootbala:/home/bala

To display the range of fields specify start field and end field as shown below. In this example, we are selecting field 1 through 4, 6 and 7

$ grep "/bin/bash" /etc/passwd | cut -d':' -f1-

4,6,7root:x:0:0:/root:/bin/bashbala:x:1000:1000:/home/bala:/bin/bash

65. Select Fields Only When a Line Contains the Delimiter

In our /etc/passwd example, if you pass a different delimiter other than : (colon), cut will just display the whole line.

In the following example, we’ve specified the delimiter as | (pipe), and cut command simply displays the whole line, even when it doesn’t find any line that has | (pipe) as delimiter.

$ grep "/bin/bash" /etc/passwd | cut -d'|' -f1root:x:0:0:root:/root:/bin/bashbala:x:1000:1000:bala,,,:/home/bala:/bin/bash

But, it is possible to filter and display only the lines that contains the specified delimiter using -s option.

The following example doesn’t display any output, as the cut command didn’t find any lines that has | (pipe) as delimiter in the /etc/passwd file.

$ grep "/bin/bash" /etc/passwd | cut -d'|' -s -f1

66. Select All Fields Except the Specified Fields

In order to complement the selection field list use option –complement.

The following example displays all the fields from /etc/passwd file except field 7

$ grep "/bin/bash" /etc/passwd | cut -d':' --complement -s -f7root:x:0:0:root:/rootbala:x:1000:1000:bala,,,:/home/bala

67. Change Output Delimiter for Display

By default the output delimiter is same as input delimiter that we specify in the cut -d option.

To change the output delimiter use the option –output-delimiter as shown below. In this example, the input delimiter is : (colon), but the output delimiter is # (hash).

$ grep "/bin/bash" /etc/passwd | cut -d':' -s -f1,6,7 --output-delimiter='#'root#/root#/bin/bashbala#/home/bala#/bin/bash

68. Change Output Delimiter to Newline

In this example, each and every field of the cut command output is displayed in a separate line. We still used –output-delimiter, but the value is $’\n’ which indicates that we should add a newline as the output delimiter.

$ grep bala /etc/passwd | cut -d':' -f1,6,7 --output-delimiter=$'\n'bala/home/bala/bin/bash

69 Install the mailx command

On Ubuntu/Debian based systems the mailx command is available from 2 different packages -

1. heirloom-mailx

2. 2. bsd-mailx

We shall be using the heirloom-mailx package because it has more features and options.

On CentOS/Fedora based systems, there is only one package named "mailx" which is the heirloom package.

To find out what mailx package is installed on your system, check the "man mailx" output and scroll down to the end and you should see some useful information.

# ubuntu/debian$ sudo apt-get install heirloom-mailx # fedora/centos$ sudo yum install mailx