CMT3321 (02/03) 
(Linux study guide 2 - basic commands)
For Lab. 2, 3


Lecturer : Mr. Lee Bo-sing (Joe)
Basic commands (1)
Basic commands (2)
Basic commands (3) - find
?	Function : search for set of files with specified characteristic in a directory 
hierarchy, starting from specified directory.
?	Syntax :  find    starting_dir_pathname   expression_for_file_characteristic
?	Expression includes :
–	-name "x"  (by filename,  x is wildcard for filename)  
–	-type  x  (by file type, x = b,c,d,f,l)
–	-user "x" (by file owner name x)
–	-group "x" (by group name  x)
–	-size  +nc (file size greater than n byte)
–	-size  -nc (file size less than n  byte)
–	-size  nc (file size equals to  n byte)
Basic commands (4) - find
–	-mtime  +x  (modified more than x days ago)
–	-mtime  -x  (modified less than x days ago)
–	-mtime  x  (modified exactly at  x days ago)
–	-printf  "%m\t%u\t%g\t%s\t%t\t%p\n" (print searched files in format of ls -ld)
?	Components of expression can be combined in logical NOT, AND, OR 
:
–	NOT :    !expr
–	AND :    expr1  -a  expr2 
–	                expr1  expr2
–	OR :  expr1  -o   expr2
?	Demo with file  find_demo.ksh
Basic commands (5) - cat
?	Function :
–	Display content of file.
–	Drawback :if  size of file is more than one page, you have to scroll up to 
view content of first page 
–	Eg. cat filename
–	Can it work for wildcard ?
–	Concatenate content of 2 or more files 
–	Eg.  cat  file1  file2   >   file3
–	Content of  file3 will be content of file1 + file2

Basic commands (6) – less
?	Function : read content of file page by page, with fast movement and pattern 
search function
?	Syntax :  less filename
?	Move to beginning of file : press g
?	Move to beginning of file : press G
?	Forward one page : press ctrl-f 
?	Backward one page :  press ctrl-b
?	Search pattern :  /pattern   (n for next downward search, N for next upward 
search)
?	Quit  : press q
?	Actually, its function key definition is similar to that of vi
?	Note that "more filename" can also read content of file page by page. Its function 
is much less than "less filename"


Basic commands (7) – head, tail
?	head   filename  : view first 10 lines of file
?	head  -30   filename  : view first  30 lines of  file
?	tail  filename  :  view last 10 lines of file
?	tail  -25  filename  :  view last 25 lines of file



Basic commands (8) - ls
?	Function : list name of filename/subdir. in a directory
?	Syntax :   ls   -options   
wildcard_for_filename_or_subdirname
?	Options :
–	-a   (show all files, including hidden files, wildcard must match if 
you want to show hidden files)
–	-l    (display long format)
–	-d   (does not list recursively)
–	-i    (list inode number)
Basic commands (9) - wc
?	Function of wc :  Count  number of lines, words and 
characters in a file
?	Syntax  :  wc  -option filename
?	Option : 
–	-l   (show number of lines only)
–	-w  (show number of words only)
–	-c   (show number of characters only)
?	Output of "wc   filename"
–	Num_of_line    num_of_word   num_of_char     filename

Basic commands (10) - file
?	Function : a quick way to find out classification of files for a 
specified set of files
?	Classification includes : ascii  text, executable binary, link,  
character special, block special, empty,  image, directory
?	How to use  :  file  wildcard   | more
Basic commands (11) – diff,  cmp
?	diff :
–	Function : compare 2 ascii text file
–	Syntax : diff   file1    file2
–	Difference will be shown line by line.
?	cmp :
–	Function : compare 2 binary files
–	Syntax : cmp  -s  file1    file2
?	-s  suppress output and return status :
–	0  ( 2 files are identical)
–	1   (2 files are different)
–	2   (some error occurs)
?	Often used in script



Basic commands (12) - grep
?	Function : search for some pattern specified in regular 
expression format in a file or standard input.
–	Working on file 
?	grep     "pattern"     filename
?	Eg.  grep    bslee    /etc/passwd
?	Very useful in working with pipeline
?	Eg.  file  *  |  grep   dir
?	Eg.  ps   –aux      | grep   root
Basic commands (13) – sort
?	Function : sort lines of ascii text file or stdin by some specified 
criteria. The ascii text file can be a database file.
?	Result is output to stdout => can be piped
?	The default sorting order is lexical order.
?	With appropriate option, it assumes each line has several fields 
separated by specified separator. 
?	Default field separator is white space (i.e. space,  tab)


Basic commands (14) - sort
?	Syntax  :  sort  -option   text_filename
?	Option :
–	-n   (numeric order)
–	-d  (consider only blank & alphanumeric characters)
–	-f   (ignore case)
–	-r   (reverse output order)
–	-t?   (specify field separator as ? )
–	+n    (specify field n as starting sorting key)
–	-m    (specify field m as ending sorting key)
–	(n, m is numbered starting at 0)
?	Demo with  file sort_demo.ksh

Basic commands (15) - uniq
?	Function :  remove duplicate lines from a sorted ascii text file or stdin
?	Assume field separator is  white space
?	Syntax :  uniq  -option  text_filename
?	Option : 
?	-c   (prefix lines by number of occurrence)
?	-i    (ignore case)
?	-d   (display duplicated lines only)
?	-u   (display unique  lines only)
?	-n   (ignore  first  n fields)
?	+n   (ignore first n characters)
?	Drawback : cannot specify field separator, particular field(s)  to ignore
?	How to solve it ?
?	Demo with file  uniq_demo.ksh  , uniq_target
Basic commands (16) – cut & paste
?	Cut :
–	Function : split a text file or stdin vertically
–	Syntax :  cut  -options  text_filename
–	Options :
?	-d"?"     (specify field separator as ?)
?	-fn1,n2    (select field n1, n2.   Field number starts as 1)
?	-fn1-n3    (select from field n1 to n3)
?	-f-n1        (select from first field to field n1)
?	-fn1-        (select from field n1 to last field)

Basic commands (17) – cut & paste
?	Paste :
?	Function : merge 2 or more files vertically
?	Syntax :  paste  -options  file1    file2  …..
?	Options :
?	-d"?"       (specify field separator as ?)
?	Think about 2 methods of changing the field separator of a 
file
?	Demo with file cut_demo.ksh
Basic commands (18) – split
?	Function : cut a text file horizontally into several files
?	Syntax : split  -option  original_file   prefix_of_result_file
?	Option :  -ln    (each output file contains n line(s) of original file)
?	Several files will be output and named as  prefixaa, prefixab,  
prefixac, …..
?	Demo with file split_demo.ksh,  split_target
?	How to paste 2 or more files horizontally?
Basic commands (19) - gzip
?	Function : losslessly compress or decompress one or more files (ordinary or 
directory only).
?	Keep access mode, ownership, time-stamp (create, access & modify time) on 
compression and decompression
?	Each target file will be compressed and "filename" changes to "filename.gz"
?	Syntax :  gzip  -option  wildcard_for_target_files
?	Option :
–	-r   (recursively down a directory)
–	-d    (decompress) 
?	bzip2 is getting popular because of better compression ratio

Basic commands (20) - tar
?	Function : archive one or more file into another tar file 
either for transfer or tape archive
?	Ordinary, directory, link file can be tared. For link file, it 
only tar the link file but the target point to by link file
?	Extension of tar file  is usually .tar  , for human recognition
?	Demo with file tar_demo.ksh
Basic commands (21) - tar
?	Syntax : tar  -options   tar_filename      
wildcard_for_target_files
?	Options :
–	-c   (create new archive or tar file)
–	-f    (specify name of tar file)
–	-r    (append file to end of tar file)
–	-v    (verbosely)
–	-x    (extract  a tar file)
–	-t    (list content of a tar file, can only work on uncompressed tar 
file)
–	-z    (compress after tar)

Basic commands (22) – at
?	at : schedule a job/script/program to run at a later time/date
?	Syntax :  at  -options  time
–	-l    (list  scheduled jobs at queue)
–	-d    job_id   (remove job of job_id  from at queue)
–	-f   pathname_of_script_or_command_to_run
?	Time can  now+1minute, now+2hour, now+3day,  
now+1month, now+1year, 1300, 2330, etc… 
?	Demo with file at_demo.ksh




Basic commands (23) – at
?	Daemon /etc/rc.d/init.d/atd must be started
?	Not everyone can run above commands. Controlled by 2 
configuration file : /etc/at.deny,   /etc/at.allow
–	If the file /etc/at.allow exists,  only  usernames  mentioned  in  it  are  allowed 
to use at.
–	If  /etc/at.allow  does not exist, /etc/at.deny is checked, every username not 
mentioned in it is then allowed to use at.
–	If neither exists, only the superuser is allowed use of at.
–	An empty /etc/at.deny means that every user is allowed use these commands, 
this is the default configuration.


Basic commands (24) – crontab
?	Jobs scheduled by "at" only run once. To periodically run jobs at 
scheduled time, you can use crontab. 
?	You only need to configure one time.
?	crontab  –e
–	Content to input : refer to file cron_example
?	To edit : crontab –e 
?	To list : crontab –l
?	To remove  : crontab –r
?	Demo with file cron_example,  incre.ksh



Basic commands (25) – crontab
?	Daemon /etc/rc.d/init.d/crond must be started 
?	Not everyone can run above commands. Controlled by 2 
configuration file : /etc/cron.deny,   /etc/cron.allow 
–	If the cron.allow file exists, then you must be listed there in order  to  be 
allowed  to  use  this  command.  
–	If the cron.allow file does not exist but the       deny file does exist, then you 
must not be listed  in  the  cron.deny  file  in order to use this command. 
–	If neither of these files exists, then depending on site-dependent configuration 
parameters




Basic commands (26) - tr
?	Function : translate ascii characters into different ascii 
characters of same length. 
?	Works on stdin 
?	Work with pipeline
?	Syntax :  tr   'src_string'   'dest_string'
?	Eg.  cat  file1  | tr   'abc'     'ABC'  >  file2
?	Eg.  cat  file1  | tr   'abc'     '123'   > file3
?	  application is limited as length of src_string and dest_string 
must be the same



Basic commands (27) 
?	which 
?	uname –a
?	hostname
?	date  
?	date +%Y%m%d%H%M%S
?	df –k
?	du   –sk    dir_pathname
?	who
?	whoami
?	su
 

Open 
Discussions
Exercise (1)
?	a. Name the command to find out linux kernel version?
?	b. How to find out used % of your root partition. Please name the 
command and options used.
?	c. login as root, find out & list, with format similar to "ls –ld ", all 
the files under dir.  /etc with following criteria :
–	Filename starting with ta
–	Filename starting with ta and filesize smaller than 100byte
–	Filename starting with a and file type is link
–	Filename starting with a and file owner is "news"


Exercise (2) -1
?	a. Find out the detailed file type (more than the 4 types) of following files : 
–	/bin/vi,   /bin/view, /etc/passwd,  /dev/fd0, /dev/had,  /dev/isdn1,   /bin/, 
/etc/rc.d/init.d/crond,  /boot/vmlinuz-2.4.18-3, /boot/initrd-2.4.18-3.img  
?	b. Create a subdirectory , named "lab2_3", under your home directory. Ftp 
download script $HOME/student_cp.ksh & $HOME/at_cron.ksh from 
158.182.111.18 into $HOME/lab2_3/. Username & password is anonymous and 
any respectively. Run script student_cp.ksh. This script will copy all files 
(except /bin/,  /dev/fd0, /dev/had, /dev/isdn1) in part a to dir. "lab2_3"
?	c. after copying,  how to use one command to know sum of filesize of all files in 
$HOME/lab2_3/ ?

Exercise (2) - 2
?	$HOME/lab2_3/passwd is a file containing information of each user account 
with following format :
Username:password:usid:gid:comment:home-dir:shell-type 

?	d. How to check for existence of username of  "root", "bin", "daemon" and find out their usid 
and home-dir?
?	e.  What command can easily find out total number of accounts in file $HOME/lab2_3/passwd ?
?	f. copy $HOME/lab2_3/passwd   to $HOME/lab2_3/passwd.new   and compare these 2 files
?	g. modify first and second lines of file $HOME/lab2_3/passwd.new with any editor and 
compare these 2 files again.
?	h. how to generate a new file $HOME/lab2_3/passwd_2 which contains only username, usid, 
home-dir fields, separated by "|", for each account.
?	i. how to generate another file $HOME/lab2_3/passwd_3 which is sorted by value of usid of file 
in part g.





Exercise (3)
?	a. archive all files in dir. $HOME/lab2_3/ into a single file, named 
"tarfile.tar", without compression.
?	b. how to list what files are archived in "tarfile.tar"
?	c. create a dir. $HOME/lab2_3/ extract/ and extract all files in 
"tarfile.tar" into this new dir.
?	d. compress all files $HOME/lab2_3/ extract/ 
Exercise (4)
?	What is done by script at_cron.ksh : 
–	create a new file $HOME/lab2_3/filesize if this file does not exist. 
–	Then append "Hello….\n" to this file.
?	a. schedule script $HOME/lab2_3/at_cron.ksh to run at one minute 
later once. What is the result?
?	b. redo part a but schedule to run at 9:10 p.m. What is the value of 
job id?
?	c. schedule script $HOME/lab2_3/at_cron.ksh to run at every 1 
minute & observe the result 2 minutes later.
?	d. un-schedule what you done in part c.