50MostFrequentlyUsedUNIX/LinuxCommands(WithExamples)（1）
This article provides practical examples for 50 most frequently used commands in Linux / UNIX.
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This is not a comprehensive list by any means, but this should give you a jumpstart on some of the common Linux commands. Bookmark this article for your future reference.
Did I miss any frequently used Linux commands?Leave a commentand let me know.
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
More tar examples:The Ultimate Tar Command Tutorial with 10 Practical Examples
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" *
More grep examples:Get a Grip on the Grep! – 15 Practical Grep Command Examples
3. 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
# find ~ -empty
More find examples:Mommy, I found it! — 15 Practical Linux Find Command Examples
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
More ssh examples:5 Basic Linux SSH Client Commands
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/ /'
More sed examples:Advanced Sed Substitution Examples
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
More awk examples:8 Powerful Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR
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
More vim examples:How To Record and Play in Vim Editor
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
More diff examples:Top 4 File Difference Tools on UNIX / Linux – Diff, Colordiff, Wdiff, Vimdiff
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 p_w_picpaths to external hard-drive
# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory
Search all jpg p_w_picpaths in the system and archive it.
# find / -name *.jpg -type f -print | xargs tar -cvzf p_w_picpaths.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
More ls examples:Unix LS Command: 15 Practical Examples
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
More cd examples:6 Awesome Linux cd command Hacks
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
More bzip2 examples:BZ is Eazy! bzip2, bzgrep, bzcmp, bzdiff, bzcat, bzless, bzmore examples
17. unzip 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
More ftp examples:FTP and SFTP Beginners Guide with 10 Examples
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
More crontab examples:Linux Crontab: 15 Awesome Cron Job Examples
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 status 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
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.
$ top -u oracle
More top examples:Can You Top This? 15 Practical Linux Top Command Examples
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