Linux Unix Commands

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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 "atithya" *



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



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



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. 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



8. 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



9. 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



10. ls command examples

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

$ ls -lh
-rw-r----- 1 atithya 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



11. 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.

12. cd command examples

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

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

13. 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



14. bzip2 command examples

To create a *.bz2 compressed file:

$ bzip2 test.txt



To uncompress a *.bz2 file:

bzip2 -d test.txt.bz2



15. 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



16. 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



16. 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



17. 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



Courtesy: The Geek Stuff