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" *
First
create the following demo_file that will be used in the examples below to
demonstrate grep command.
$ cat demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
This Line Has All Its First Character Of The Word With Upper Case.
Two lines above this line is empty.
And this is the last line.
1. Search for the given string in a single file
The basic
usage of grep command is to search for a specific string in the specified file
as shown below.
Syntax:
grep "literal_string" filename
$ grep "this" demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.
2. Checking for the given string in multiple files.
Syntax:
grep "string" FILE_PATTERN
This is also a basic usage of grep command. For this example, let us copy the
demo_file to demo_file1. The grep output will also include the file name in
front of the line that matched the specific pattern as shown below. When the
Linux shell sees the meta character, it does the expansion and gives all the
files as input to grep.
$ cp demo_file demo_file1
$ grep "this" demo_*
demo_file:this line is the 1st lower case line in this file.
demo_file:Two lines above this line is empty.
demo_file:And this is the last line.
demo_file1:this line is the 1st lower case line in this file.
demo_file1:Two lines above this line is empty.
demo_file1:And this is the last line.
3. Case insensitive search using grep -i
Syntax:
grep -i "string" FILE
This is also a basic usage of the grep. This searches for the given
string/pattern case insensitively. So it matches all the words such as “the”,
“THE” and “The” case insensitively as shown below.
$ grep -i "the" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS
FILE.
this line is the 1st lower case line in this
file.
This Line Has All Its First Character Of The
Word With Upper Case.
And this is the last line.
4. Match regular expression in
files
Syntax:
grep "REGEX" filename
This is a very powerful feature, if you can use use regular expression
effectively. In the following example, it searches for all the pattern that
starts with “lines” and ends with “empty” with anything in-between. i.e To
search “lines[anything in-between]empty” in the demo_file.
$ grep "lines.*empty" demo_file
Two lines above this line is empty.
From documentation of grep: A regular expression may be
followed by one of several repetition operators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{,m} The preceding item is matched at most m times.
{n,m} The preceding item is matched at least n times, but not
more than m times.
5. Checking for full words,
not for sub-strings using grep -w
If you want to search for a
–
word, and to avoid it to match the substrings use -w option.
Just doing out a normal search will show out all the lines.
The following example is the regular grep where it is searching for “is”. When
you search for “is”, without any option it will show out “is”, “his”, “this”
and everything which has the substring “is”.
$ grep -i "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS
FILE.
this line is the 1st lower case line in this
file.
This Line Has All Its First Character Of The
Word With Upper Case.
Two lines above this line is empty.
And this is the last line.
The following example is the WORD grep where it is searching only for the word
“is”. Please note that this output does not contain the line “This Line Has All
Its First Character Of The Word With Upper Case”, even though “is” is there in
the “This”, as the following is looking only for the word “is” and not for
“this”.
$ grep -iw "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS
FILE.
this line is the 1st lower case line in this
file.
Two lines above this line is empty.
And this is the last line.
6. Displaying lines
before/after/around the match using grep -A, -B and -C
When doing a grep on a huge file, it may be useful to see
some lines after the match. You might feel handy if grep can show you not only
the matching lines but also the lines after/before/around the match.
Please create the following demo_text file for this example.
$ cat demo_text
4. Vim Word Navigation
You may want to do several navigation in
relation to the words, such as:
* e -
go to the end of the current word.
* E -
go to the end of the current WORD.
* b -
go to the previous (before) word.
* B -
go to the previous (before) WORD.
* w -
go to the next word.
* W -
go to the next WORD.
WORD - WORD consists of a sequence of
non-blank characters, separated with white space.
word - word consists of a sequence of
letters, digits and underscores.
Example to show the difference between WORD
and word
*
192.168.1.1 - single WORD
*
192.168.1.1 - seven words.
6.1 Display N lines after match
-A is the option which prints the specified N lines after the
match as shown below.
Syntax:
grep -A <N> "string" FILENAME
The following example prints the matched line, along with the 3 lines after it.
$ grep -A 3 -i "example" demo_text
Example to show the difference between WORD
and word
* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.
6.2 Display N lines before match
-B is the option which prints the specified N lines before
the match.
Syntax:
grep -B <N> "string" FILENAME
When you had option to show the N lines after match, you have the -B option for
the opposite.
$ grep -B 2 "single WORD" demo_text
Example to show the difference between WORD
and word
* 192.168.1.1 - single WORD
6.3 Display N lines around match
-C is the option which prints the specified N lines before
the match. In some occasion you might want the match to be appeared with the
lines from both the side. This options shows N lines in both the side(before
& after) of match.
$ grep -C 2 "Example" demo_text
word - word consists of a sequence of
letters, digits and underscores.
Example to show the difference between WORD
and word
* 192.168.1.1 - single WORD
7. Highlighting the search
using GREP_OPTIONS
As grep prints out lines from the file by the pattern /
string you had given, if you wanted it to highlight which part matches the
line, then you need to follow the following way.
When you do the following export you will get the highlighting of the matched
searches. In the following example, it will highlight all the this when you set
the GREP_OPTIONS environment variable as shown below.
$ export GREP_OPTIONS='--color=auto'
GREP_COLOR='100;8'
$ grep this demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.
8. Searching in all files
recursively using grep -r
When you want to search in all the files under the current
directory and its sub directory. -r option is the one which you need to use.
The following example will look for the string “ramesh” in all the files in the
current directory and all it’s subdirectory.
$ grep -r "ramesh" *
9. Invert match using grep -v
You had different options to show the lines matched, to show
the lines before match, and to show the lines after match, and to highlight
match. So definitely You’d also want the option -v to do invert match.
When you want to display the lines which does not matches the given
string/pattern, use the option -v as shown below. This example will display all
the lines that did not match the word “go”.
$ grep -v "go" demo_text
4. Vim Word Navigation
You may want to do several navigation in
relation to the words, such as:
WORD - WORD consists of a sequence of
non-blank characters, separated with white space.
word - word consists of a sequence of
letters, digits and underscores.
Example to show the difference between WORD
and word
* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.
10. display the lines which
does not matches all the given pattern.
Syntax:
grep -v -e "pattern" -e
"pattern"
$ cat test-file.txt
a
b
c
d
$ grep -v -e "a" -e "b"
-e "c" test-file.txt
d
11. Counting the number of
matches using grep -c
When you want to count that how many lines matches the given
pattern/string, then use the option -c.
Syntax:
grep -c "pattern" filename
$ grep -c "go" demo_text
6
When you want do find out how many lines matches the pattern
$ grep -c this demo_file
3
When you want do find out how many lines that does not match the pattern
$ grep -v -c this demo_file
4
12. Display only the file
names which matches the given pattern using grep -l
If you want the grep to show out only the file names which
matched the given pattern, use the -l (lower-case L) option.
When you give multiple files to the grep as input, it displays the names of
file which contains the text that matches the pattern, will be very handy when
you try to find some notes in your whole directory structure.
$ grep -l this demo_*
demo_file
demo_file1
13. Show only the matched
string
By default grep will show the line which matches the given
pattern/string, but if you want the grep to show out only the matched string of
the pattern then use the -o option.
It might not be that much useful when you give the string straight forward. But
it becomes very useful when you give a regexp
pattern and trying to see what it matches as
$ grep -o "is.*line" demo_file
is line is the 1st lower case line
is line
is is the last line
14. Show the position of match
in the line
When you want grep to show the position where it matches the
pattern in the file, use the following options as
Syntax:
grep -o -b "pattern" file
$ cat temp-file.txt
12345
12345
$ grep -o -b "3" temp-file.txt
2:3
8:3
Note: The output of
the grep command above is not the position in the line, it is byte offset of
the whole file.
15. Show line number while
displaying the output using grep -n
To show the line number of file with the line matched. It
does 1-based line numbering for each file. Use -n option to utilize this
feature.
$ grep -n "go" demo_text
5: * e - go to the end of the current word.
6: * E - go to the end of the current WORD.
7: * b - go to the previous (before) word.
8: * B - go to the previous (before) WORD.
9: * w - go to the next word.
10: * W - go to the next WORD.
. find
command examples
Find files using file-name ( case
in-sensitve find)
# find -iname "MyCProgram.c"
Execute commands on files found by
the find command
$ find -iname "MyCProgram.c" -exec md5sum {} \;
Find all empty files in home
directory
4. ssh
command examples
Login to remote host
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
. 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.
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
Go to the first match of the
specified
$ vim +/search-term filename.txt
Open the file in read only mode.
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 a file in descending order
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
Visual Classification of Files
With Special Characters Using 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:
To uncompress a *.gz file:
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:
To uncompress a *.bz2 file:
17.
unzip command examples
To extract a *.zip compressed
file:
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 the system after 10
minutes.
Reboot the system using shutdown
command.
Force the filesystem check during
reboot.
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
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:
Check the status of all the
services.
Restart a service.
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.
To view current running processes
in a tree structure. H option stands for process hierarchy.
23. free
command examples
This command is used to display
the free, used, swap memory available in the system.
Typical free command output. The
output is displayed in bytes.
$ free
total used free shared buffers cached
Mem: 3566408 1580220 1986188 0 203988 902960
-/+ buffers/cache: 473272 3093136
Swap: 4000176 0 4000176
If you want to quickly check how
many GB of RAM your system has use the -g option. -b option displays in bytes,
-k in kilo bytes, -m in mega bytes.
$ free -g
total used free shared buffers cached
Mem: 3 1 1 0 0 0
-/+ buffers/cache: 0 2
Swap: 3 0 3
If you want to see a total memory
( including the swap), use the -t switch, which will display a total line as
shown below.
ramesh@ramesh-laptop:~$ free -t
total used free shared buffers cached
Mem: 3566408 1592148 1974260 0 204260 912556
-/+ buffers/cache: 475332 3091076
Swap: 4000176 0 4000176
Total: 7566584 1592148 5974436
24. top
command examples
top command displays the top
processes in the system ( by default sorted by cpu usage ). To sort top output
by any column, Press O (upper-case O) , which will display all the possible
columns that you can sort by as shown below.
Current Sort Field: P for window 1:Def
Select sort field via field letter, type any other key to return
a: PID = Process Id v: nDRT = Dirty Pages count
d: UID = User Id y: WCHAN = Sleeping in Function
e: USER = User Name z: Flags = Task Flags
........
To displays only the processes
that belong to a particular user use -u option. The following will show only
the top processes that belongs to oracle user.
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.
It is very useful while giving shell metacharacters in the file
name argument.
Print the filename and get confirmation before removing the
file.
Following example recursively removes all files and directories
under the example directory. This also removes the example directory itself.
28. cp command examples
Copy file1 to file2 preserving the mode, ownership and
timestamp.
Copy file1 to file2. if file2 exists prompt for confirmation
before overwritting it.
29. mv command examples
Rename file1 to file2. if file2 exists prompt for confirmation
before overwritting it.
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.
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.
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.
Revoke all access for the group (i.e read, write and execute )
on a specific file.
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.
Super user can use passwd command to reset others password. This
will not prompt for current password of the user.
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.
35. mkdir command examples
Following example creates a directory called temp under your
home directory.
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.
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.
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.
1. General
commands
2. System
calls
3. C
library functions
4. Special
files (usually devices, those found in /dev) and drivers
5. File
formats and conventions
6. Games
and screensavers
7. Miscellaneous
8. 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.
Print N number of lines from the file named 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.
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.
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.
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 -c 'ls'
[john@dev-server]$
Login to a specified user account, and execute the specified
shell instead of the default shell.
$
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.
If you want to specify the mysql root password in the command
line itself, enter it immediately after -p (without any space).
46. yum command examples
To install apache using yum.
To upgrade apache using yum.
To uninstall/remove apache using yum.
47. rpm command examples
To install apache using rpm.
#
rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm
To upgrade apache using rpm.
#
rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm
To uninstall/remove apache using rpm.
48. ping command examples
Ping a remote host by sending only 5 packets.
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. wget command examples
The quick and effective method to download software, music,
video from internet is using wget command.
$
wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz
Download and store it with a different name.
$
wget -O taglist.zip http://www.vim.org/scripts/download_script.php?src_id=7701
