Unix Basic Interview questions and commands

Frequently used UNIX commands

Command	Result
ls	lists files in current working directory
ls *.out	lists all files in current directory that end in .out
ls -l	lists files giving details including file size
pwd	displays full-path name of your current working directory on screen (stands for “present working directory”)
cd dirname	changes directory to dirname
cd ..	changes directory to one above the current directory
cd	with no argument, takes you to your home directory
mkdir dirname	creates new directory dirname
rmdir dirname	removes empty directory dirname
cp filename newname	makes a copy of filename with the name newname
cp ../filename .	copies filename in directory one tier above to current directory giving it the same name
mv filename newname	renames filename to newname (mv stands for “move”)
cat filename	displays contents of filename on screen
more filename	displays filename contents one screen at a time (Enter key scrolls through file by line; space bar scrolls through by screen)
head filename	displays first 10 lines of filename on screen
tail filename	displays last 10 lines of filename on screen
rm filename	deletes filename without double check (rm stands for “remove”)
grep string filename	displays lines from filename containing string on screen
./ filename &	runs job filename in the background
qsub filename	sends job filename to queue (where qsub is a submission script file in your bin directory)
qstat	lists jobs running on queue
qstat -a	lists only your jobs
qdel job#	deletes job with number job# from queue
ps	lists processes you have running
ps -ef	lists all processes
kill pid#	kills process with ID number pid#
kill -9 pid#	kills (with the “sure kill” signal) process with ID number pid#
kill -kill 0	kills all processes you have running and logs you off
man commandname	displays manual page for command commandname
man -k keyword	lists manual pages for commands related to keyword
lp filename	prints filename on printer in room 4241
chmod ### filename	changes “read, write, execute” mode of filename Example: to set the privileges for filename so that the owner has the ability to read, overwrite and execute the file, the group has the ability to read and execute the file, and everyone else has no access to the file, use the command chmod 750 filename.
	owner	group	all
	rwx	rwx	rwx
	4 2 1	4 2 1	4 2 1
	sum numbers for each of the three categories of user
Ctrl+c	kills current operation
Ctrl+h	delete (always works even when delete key doesn’t)
Ctrl+d	logout

Frequently used Vi Editor commands

Command	Result
vi filename	opens file (vi with no argument opens new file)
Two modes in vi editor: insert and command (default is command mode when file is opened)
i	change to insert mode - in this mode you can add text
Esc	return to command mode
in command mode →
	:q	quit file
	:q!	quit file without saving any changes
	:w	save file (write)
	:wq	save and quit file (write and quit)
	x	delete character
	/string	search forward for string (n key finds next)
	?string	search backwards for string (n key finds previous)
	:g/string/s//string2/g	substitute string with string2 globally
	:line#	jump to line# in file
	:$	jump to last line of file
	:.,$d	delete from current line to end of file
	:.,.+20d	delete from current line through next 20