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Monday, February 05, 2007

A CASUAL GUIDE TO SOME COMMONLY USED LINUX COMMANDS

(Part 1)

Through this document i try to explain some of the commonly used commands under linux and their basic use In this first part of series we cover ls,cat,arch,bzip2,gzip,tar,pwd,more,mpg123



1. cat : ( concatenate)


This command can be used for diplaying content of a file on the console, combining two files into a single file , or appending content of one or more files into a single file commonly.

cat v1 This statement would display the file named v1 on the console

cat v1 v2 v3 > v4 This statement would combine the content of textfile v1,v2,v3 and create a new file v4 having all the content of three files.

cat v4 >> v5 This statement would append v4 file at the end of file v5. To end the statement type (Ctrl + D (EOF))

cat > filename << STOP This statement would create a filenamed filename at the console and aaccept input from the user for the file , the file is ended(terminated ) on typing Ctrl + D.



2. arch


The command would print the machine architecture to the standard outpit (console)

Example :- On my Pentium M-1.4 ghz laptop it printed

i686


3. ls


The ls command lists the files at command line and has a number of options for displaying the file at the command line , the manpage on ls is as huge as huge gets . Some important options while ls are : -


ls command normally dosent display the hidden files and folders the one starting with . when used normally however if you want to display the hidden files and folder it can be done by using the -a option .



ls -a : Displays all files and folders including the hidden one


The above command displays current directory and parent director by ./ and ../ however if you want to avoid displaying this use -A option instead of -a option.


ls -S : the -S option displays the file list in a sorted fashion with the biggest sized file displayed first


ls -sS : the -s option displays file size before the filename combined with -S option it displays a sorted list of files currently in directory with the filesize infront of the filename.


ls -Sr : the -r option combined with -S displays the sorted list of files in the current directory with the smallest sized file displayed first.

ls -sSh : the command displays the sorted list of files in the directory with the file size displayed in a more understandable fashion.

ls -F : this command displays the list of files and directory with directories ending with (/) , executable files with (*) , Symbolic links with ( @)

ls -l : this command displays the file list with additional information like size,date (editited ,modified ) etc

ls -t: displays the direvtory in the order of their age with youngest directory displayed first adding -r tag could reverse the order.



4. gzip (GNU Zip)


gzip can be used for compressing a single file , it is not meant for compressing entire directories as other file formats do . The default extension used bu gzip archives is (.gz) .

gzip filename.ext would create a file name filename.gz and replace the existing filename.ext file with filename.ext.gz file which is compressed gzip archive , the gzip command retains the file's attributes the modification,time stamp, access etc.

The compression level of the file can be varied by using options from 1 to 9 while compressing a file

gzip -1 filename.ext would compress the file quicker but with less compression.

gzip -9 filename.ext would compress the file slower but with more compression.

the default compression level is 6.

The filesize of compressed gzip archive would depend on the orignal file format it would do well with a non - archived file such as txt,doc,bmp etc but would fair poorly with JPG , PNG etc which are already compressed by some algorithm.

The gzipped file can be decompressed by using the gzip -d or gunzip command at the command line.

the default file extension used by gzip archives is .gz if you want to use a different file extension it could be done by using the -S option
example : gzip -S .x filename.ext would create a archive by the name of filename.ext.x

5. tar ( Tape archiver )

The tar program combines a number of files and directory in a single file which then can be compressed using a gzip or bzip2 program to reduce it's file size.

tar -cvf file.tar file1 file2 file3 file4 : This would create a tar archive combining the file1 file2 and file3 into a single file the archive have the same name as the file1 since we have specified the -f option which makes tar use the first option as the filename of the archive , -c tells the tar program to create a archive and -v option displays all the background information on the screen.

tar -cvf file.tar file1.tar file/ : This command would create a archive named file.tar with file1.tar and file subdirectory as the content of the archive .

tar -cvzf file.tar.gz file1 file2 file3 file/ : This command would create a tar file consisiting of the files and directory specified and then the file is compressed using the gzip program, to create a final archive file.tar.gz.

tar -cvjf file.tar.bz2 file1 file2 file3 file/ : This command would create a tar file consisiting of the files and directory specified and then the file is compressed using the bzip2 program, to create a final archive file.tar.bz2

tar -xvf file.tar : This command would extract all the files contained in the tar file file.tar

tar -xvjf file.tar.bz2 : This command would extract all the files contained in the file file.tar.bz2 , it would first call the bzip2 program to extract the file.tar and the call tar to extract the file.tar and it's conetent.

tar -xvzf file.tar.gz : This command would extract all the files contained in the file.tar.gz , it would first call the gzip program to extract the file.tar and then call tar to extract file.tar and it's content.

If you have created the file.tar but want to add some file(s) later it can be done using the following command and using the -rf option .
tar -rf file.tar file(s)


6. bzip2

The bzip2 is similar to gzip program but compresses file better and more effectively as compared to gzip program . The default extension used by bzip2 program is (.bz2) , the usage of bzip2 is very similar to the gzip program but has some additional options , which are described here .

bzip2 -k filename.ext : This commmand would create a archive of the filename.ext but would also keep a copy of the orignal file unlike gzip which replaces existing file with the the new archive file.



the bzip2 program also has different compression level ranging from 1 -least to 9-maximum . which can be set by using syntax like : bzip2 -1 filename.ext


bzip2 archives can be extracted by using the bzip2 -d option or by using the program bunzip2 .



7. More


more allows one to view text file in the console with abilitty to scroll the file at shell. Syntax for using more is very simple .

To open a file type

more filename

or
more -s filename : this command shrinks multiple blank lines into a single line allowing easy modifcation of file.

some of the keyboard shortcuts are : -

(=) : This cause the current pagenumber to be displayed on the screen.

(Shift + (F)) : This causes to display the filename and path with the line number in the window.


(Q) : Quits the program


(B) : Takes the display one page back .


(v) : This would launch the default text editor which is vi allowing editing of the file the default text editor can be changed by changing the enviornmental variable EDITOR/VISUAL.


(d) : this scrolls the the displayed the file by default 11 lines which could be changed.


8. mpg123 / mpg321


mpg123 is command line based audio player that forms the backbone of number of graphically available Audio players , it is one of the most efficient player on the Linux platform and can play mp3 files on as low hardware specs as a 120Mhz Pentium Processor based computer . A similar command line application is mpg321 that can be used for playing mp3 files.



mpg123 or mpg321 file name - To play mp3 file

Ctrl + C - This skips to next track

Typing Ctrl + C Twice - quits the application

mpg123 -z *.mp3 : - Command would play all the mp3 files in the directory with a shuffled play-list.


mpg123 -w filename.wav filename.mp3 :- This command would convert the mp3 file to wav file , whic can then be used for burning on to cd to make audio cd.


However if your audio files/file is located in some location in sub-folders and u don't know exact location then following command can be used

mpg123 $ (find -name "Filename")

pwd

9. pwdThis command displays the full path of current working directory.


(Incomplete : Due to lack of time i would complete this guide later )










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