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basic linux commands

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basic linux commands

Post by Admin on Sat Jul 26, 2014 11:35 am

These are basic linux commands which is used in our day to day work ..............

pwd
prints working directory (prints to screen, ie displays the full path, or your location on the filesystem)

ls
lists contents of current directory

ls –l
lists contents of current directory with extra details

ls /home/user/*.txt
lists all files in /home/user ending in .txt


NOTE: if at any time you forget any command, syntax or switch then just type

command -h

or

command --help

.... Try these and I will let you know more interesting commands then.

cd
change directory to your home directory

cd ~
change directory to your home directory

cd /scratch/user
change directory to user on scratch

cd -
change directory to the last directory you were in before changing to wherever you are now

mkdir mydir
makes a directory called mydir

rmdir mydir
removes directory called mydir. mydir must be empty

touch myfile
creates a file called myfile. updates the timestamp on the file if it already exists, without modifying its contents

cp myfile myfile2
copies myfile to myfile2. if myfile2 exists, this will overwrite it!

rm myfile
removes file called myfile

rm –f myfile
removes myfile without asking you for confirmation. useful if using wildcards to remove files ***

cp –r dir newdir
copies the whole directory dir to newdir. –r must be specified to copy directory contents recursively

rm –rf mydir
this will delete directory mydir along with all its content without asking you for confirmation! ***

nano
opens a text editor. see ribbon at bottom for help. ^x means CTRL-x. this will exit nano

nano new.txt
opens nano editing a file called new.txt

cat new.txt
displays the contents of new.txt

more new.txt
displays the contents of new.txt screen by screen. spacebar to pagedown, q to quit

head new.txt
displays first 10 lines of new.txt

tail new.txt
displays last 10 lines of new.txt

tail –f new.txt
displays the contents of a file as it grows, starting with the last 10 lines. ctrl-c to quit.

mv myfile newlocdir
moves myfile into the destination directory newlocdir

mv myfile newname
renames file to newname. if a file called newname exists, this will overwrite it!

mv dir subdir
moves the directory called dir to the directory called subdir

mv dir newdirname
renames directory dir to newdirname

top
displays all the processes running on the machine, and shows available resources

du –h --max-depth=1
run this in your home directory to see how much space you are using. don’t exceed 5GB

ssh servername
goes to a different server. this could be queso, brie, or provolone

grep pattern files
searches for the pattern in files, and displays lines in those files matching the pattern

date
shows the current date and time

anycommand > myfile
redirects the output of anycommand writing it to a file called myfile

date > timestamp
redirects the output of the date command to a file in the current directory called timestamp

anycommand >> myfile
appends the output of anycommand to a file called myfile

date >> timestamp
appends the current time and date to a file called timestamp. creates the file if it doesn’t exist

command1 | command2
“pipes” the output of command1 to command2. the pipe is usually shift-backslash key

date | grep Tue
displays any line in the output of the date command that matches the pattern Tue. (is it Tuesday?)

tar -zxf archive.tgz
this will extract the contents of the archive called archive.tgz. kind of like unzipping a zipfile. ***

tar -zcf dir.tgz dir
this creates a compressed archive called dir.tgz that contains all the files and directory structure of dir

time anycommand
runs anycommand, timing how long it takes, and displays that time to the screen after completing anycommand

man anycommand
gives you help (manual) on anycommand

cal -y
free calendar, courtesy unix

CTRL-c
kills whatever process you’re currently doing in terminal (shell)

CTRL-insert
copies selected text to the windows clipboard (n.b. see above, ctrl-c will kill whatever you’re doing)

SHIFT-insert
pastes clipboard contents to terminal

*** = use with extreme caution! you can easily delete or overwrite important files with these.


Absolute vs relative paths.

Let’s say you are here: /home/turnersd/scripts/. If you wanted to go to /home/turnersd/, you could type:

cd /home/turnersd/.

Or you could use a relative path

cd .. (two periods) will take you one directory “up” to the parent directory of the current directory.

.
(a single period) means the current directory

..
(two periods) means the parent directory
~

means your home directory
A few examples

mv myfile ..
cp myfile ../newname
cp /home/turnersd/scripts/bstrap.pl .
cp myfile ~/subdir/newname
more ../../../myfile
moves myfile to the parent directory
copies myfile to the parent directory and names the copy newname
copies bstrap.pl to “.” i.e. to dot, or the current directory you’re in
copies myfile to subdir in your home, naming the copy newname
displays screen by screen the content of myfile, which exists 3 directories “up”

Wildcards (use carefully, especially with rm)
*
matches any character. example: ls *.pl lists any file ending with “.pl” ; rm dataset* will remove all files beginning with “dataset”
[xyz] matches any character in the brackets (x, y, or z). example: cat do[or]m.txt will display the contents of either doom.txt or dorm.txt
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