Linux fundamentals commands
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This document provides a quick reference for basic Linux commands oriented for beginners. It covers commands for managing files, users and permissions, the bash shell, processes, text manipulation, and the vi editor. Usage is permitted for non-commercial purposes with the option to request modifications. The document lists its sources and includes a version history and contents section.
![Getting Started
Virtual Consoles
•
In Red Hat: available through CTRL+ALT+F[1-6]
•
If X is running, it is available as CTRL+ALT+F7
Changing password
•
passwd
Logging-In
•
From Mac or LINUX
ssh -X your_username@hostname
•
From Windows: Open Putty and select ssh.
•
Use WinSCP software for file exchange.
Date and Time Commands
•
date
u
display date and time in UTC
R
display date and time in RFC822 (used in email messages)
•
chrony package maintains time by connecting to servers over the Internet.
•
cal
output a calendar for the current month
print calendar of current year
y
cal 2010
#output a calendar for the year 2010
Making Arithmetic Calculations
•
bc
•
supported operators: + - * / % ^ sqrt()
Generating Sequential Numbers
•
seq
w
make all generated numbers of same width
s 'b'
make b character as the separator between numbers
seq 7
seq -5 5
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![Hard and Symbolic (Soft) Links
•
ln
•
ls –l in case of soft link, it displays the link name and the referenced file
ln –s filename
Checking Free Space
•
df space usage by file systems
•
du disk space by directories and subdirectories
df –h
# -h prints size in readable format
du –h –s ~
# -s reports single directory summary
Searching Files By Names
•
locate [options] name(s)
•
slocate [options] name(s)
•
Only the files you own are searched
•
Some options are shown in the example below.
•
locate.db or slocate.db databases are used
•
updatedb or locate -u
to manually update the database
locate "*.png"
# wildcard characters can be used
locate "*.png" -q
# supress errors
locate -n 15 "*.html" # only 15 resultes returned
locate -i "*.HtmL"
# case-insensitive search
Searching Files By Names and Attributes
•
find <dirs> [conditions] [–exec cmd {} ;]
-atime n
File was last accessed n days ago
-ctime n
File was last changed n days ago
-user uname
File is owned by user uname (or user ID)
-group gname
File belongs to group gname (or group ID)
-size n[cwbkMG]b 512-byte blocks (default), c in bytes, w two-byte words, k kilobyte
-iname
case -insensitive version of –name
-o
logical operator between criteria (by default it is AND)
-not
negate (logical NOT)
-perm mode
permission bits are exactly mode (octal or symbolic).
-perm -mode
ALL of the permission bits mode are set for the file.
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![Any of the permission bits mode are set for the file.
-perm +mode
-regex pattern Full path filename (not only filename) matches regular expression
pattern.
-mtime n
Files was last modified Exactly n*24 hours ago.
-mtime +n
Files was last modified >= n*24 hours ago.
-mtime -n
Files was last modified <= n*24 hours ago.
-mmin n
Files was last modified n minutes ago.
−daystart
measure time in the options above from the beginning of the current
day instead of 24 hours ago.
-newer <file>
Files newer than <file> modification date
find . –name "*.html"
find -iname snow.png
find -user peter -group peter
find -user joe -not -group joe
find -user joe -o -user jane
find -not ( -user joe -o -user jane )
find -perm 755
# matches if mode is exactly 755
find -perm +222 # matches if anyone can write
find -perm -222 # matches if everyone can write
find -perm -002 # matches if other can write
find -size 1024k
# excatly 1 MB
find -size +1024k # over 1 MB
find -size -1024k # less than 1 MB
find ~ −empty
# find empty regular files or directories
find -size +102400k -ok gzip {} ; # OK prompte before acting
find . -regex '.*[124].*ms$'
find ~ −mtime 1
find ~ −mtime 1
# files modified exactly 24 hours ago
−daystart # modified yesterday
find ~ −mtime +356
# one year or longer ago
find ~ −mtime 2 −mtime −4 −daystart # two to four days ago
# files that were modified after May 4 of the current year
touch −t 05040000 /tmp/timestamp
find ~ −newer /tmp/timestamp
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![Users, Groups and Permissions
Change Password
•
passwd
Change Your Identity
•
su username
•
su - username
# start a login shell
User Information Commands
•
whoami
# who you are
•
groups, id
# what groups you belong to
•
users, who, w
# who is logged on
•
last
# login/reboot history
Changing File Ownership
•
chown user_name file|directory
•
chgrp group_name file|directory
chown john myfile
chown –R john dir
# operate on files and directories recursively
Changing Permissions
•
chmod mode file
where mode is: [u,g or o] [+ or -] [r, w or x] (Symbolic Method)
where mode is: 4:r 2:w 1:x (Numeric Method)
chmod o-rwx file1
chmod u-w,go-x file1
chmod +x file1
# the file is executable to all security levels
chomod 775 file1
Default File Permission
•
umask
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# if case of 0002, 664 permission for files, 775 for directories
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![bash Shell Basics
File Blobbing
*
matches zero of more characters
?
matches any single character
[a-z]
matches a range of characters
[^a-z]
matches all except the range
ls file*
ls ??file
ls file[1-9]
ls file[^6-0]
History Tricks
•
history
•
Use the up and down keys to scroll through previous commands.
•
Type Ctrl-r to search for a command in command history.
•
Esc+. to recall last argument from previous command.
•
!n re-execute command number n
Command Line Expansion
•
Command Expansion: $() or ``
•
Brace Expansion: { }
•
Arithmetic: $[]
•
Arithmetic Evaluations: + - * / ** % (Full list in Arithmetic Evaluation section in bash
man page)
•
backslash makes the next character literal and can be used as last character on line to
continue command on next line.
•
To pass special characters as a string: $'string'
•
Special backslash escape sequences:
a
Alert (rings the system bell).
b
Backspace.
e
Escape.
f
Form feed.
n
Newline.
r
Carriage return.
t
Horizontal tab.
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![v
Backslash.
NNN
•
Vertical tab.
Character whose ASCII code is NNN in octal (base 8).
Filename Expansion Characters: used with commands handling files and directories:
*
zero or more characters
?
exactly one character
[list]
one character in the list. Examples: [abc],[a-m], a[-b]c
[!list] except the characters in the list. For example: a[!b]c matches aac a-c adc, but
not abc.
echo "This system's name is $(hostname)"
echo $'Note the space belown'
# doesn't work if you use double quote
echo current date is `date`
echo file{1,3,5}
echo Area: $[ $X * $Y ]
# equivalent to $[$X*$Y]
echo Your cost: $8.00
find / -name myfile*
mv /usr/tmp/song[0−9].cdda ~/music
Local Shell Variables
•
VARIABLE=value
•
echo $VARIABLE
•
To see list of the local variables that configure the shell, see the Shell Variables section
of the bash man page.
•
Common Local Configuration Variables
PS1
the prompt
d
date
h
short hostname
t
time
u
user name
w
current working directory
!
history number of the current command
$
o
$ for superusers, # for non-privileged user
o
HISTFILESIZE
how many commands to save in history
o
COLUMNS
width of the terminal
o
LINES
height of the terminal
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![Converting Characters
•
tr converts characters in one set to corresponding characters in another set
tr 'a-z' 'A-Z' < lowercase.txt
Combining Files
•
paste combines files horizontally and separate the pasted lines by TAB by default.
paste –d: ids.txt names.txt > merged.txt
# separate the data with colon
Expanding Tabs Into Spaces
•
expand
convert the tabs in the file to spaces
expand tabfile.txt > tabfile.expanded.txt
Regular Expressions
•
Wildcard Characters
another single character
.
any single character
[abc]
any single character in the set
[a-c]
any single character in the range
[^abc] any single character not in the set
[^a-c] any single character not in the range
•
Modifiers
number of the previous character
*
zero or more of the previous char
+
one or more of the previous char
?
zero or one of pervious char
{i}
exactly i of the previous char
{i,}
i or more of the previous char
{i,j} i to j of the previous char
•
Anchors
match the beginning or end of a line or word
^
line begins with
$
word begins with
>
•
line ends with
<
word ends with
Other expressions
[:alnum:]
Alpha-numeric characters 0 to 9 OR A to Z or a to z
[:alpha:]
Control characters
[:digit:]
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Alpha character a-z A-Z
[:cntrl:]
Digits 0 to 9
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![[:graph:]
Graphics characters
[:print:]
Printable characters
[:punct:]
Punctuation " ' ? ! ; : # $ % & ( ) * + - / < > = @ [ ] ^ _ { } | ~
[:space:]
White spaces (space, tab, NL, FF, VT, CR)
[:blank:]
Space and Tab characters only
^S[^ ]* R
# the last name begins with S and first name begins with R.
^[M-Z].*[12]
# the last name begins with a letter from M to Z and where the
#
phone number ends with a 1 or 2.
'^..$'
# any word of only two characters
'^.{17}$'
#
words of exactly seventeen characters wide
[0-9]{5,10} # all number combinations between 5 and 10 number long
[a-z])$
# The is an escape characher
(.*l
# contains ls and preceeded by an open bracket
Extended Regular Expressions
•
Except word anchors, basic regular expressions requiring a preceding backslash do not
require backslash
•
Used by:
o
egrep
o
grep –E
o
awk
Extracting Text by Keyword
•
grep [OPTION]... PATTERN [FILE] ...
-i
-n
-v
-AX
-BX
to
to
to
to
to
search case-insensitively
print line numbers of matches
print lines not containing pattern
include the X lines after each match
include the X lines before each match
•
grep uses by default basic Regular Expressions
•
egrep uses Extended Regular Expressions
grep 'root' file*.doc
# this will list the file name
grep –h 'root' file*.doc
# to avoid listing the file names
grep 'ahmed' /etc/passwd
# highly advisable to use sing quote
date --help | grep year
egrep 'a{2,5}' myfile
# search for counter 2,3,4 or 5 letter a's
egrep '<bye>' myfile
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![Search and Replace
•
sed
(stream editor) uses regular expressions in search string (but not in replace)
sed 's/cat/dog/' petsfile
# makes the replacement once per line
sed 's/cat/dog/g' petsfile
# multiple changes per line
sed 's/[Cc]at/dog/g' petsfile
sed 's/<[Cc]at>/dog/g' petsfile
# search by word (not string)
sed 's/<[Cc]at>/& and dog/g' petsfile # whatever found (Cat or cat), it will
# be replaced with cat and dog
sed '10,40s/cat/dog/g' petsfile
# only lines from 10 and 40 searched
sed '/begin/,/end/s/cat/dog/' petfiel # search will start from the line
#
containing "begin" to the line
#
containing "end"
sed –e 's/cat/dog/g' –e 's/cow/goat/g' petsfile # multiple find and replaces
Editing Text by awk
•
awk
•
All extended regular expressions work except curly brace counters. To use them, use -posix or --re-interval options.
awk ' { print } ' myfile
# equivalent to cat command
awk '/bye/ { print } ' myfile
# print lines containing the pattern
awk '/[2-5]+/ { print } ' myfile
awk ' { print $2, $1 } ' myfile
awk ' { print $2 "
Page 26
# print fields 2 and 1 in a space separated
# text file.
" $1 } ' myfile
# in a tab separated file
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![Managing Processes
Listing Processes
•
top continuously updated list
•
ps shows processes from the current terminal by default
o
-a
all processes except session leaders and processes not associated with a
terminal.
o
-A
prints all processes. Identical to -e.
o
-e
prints all processes. Identical to -A.
o
-H
show process hierarchy
o
–u
prints process owner information
o
–l
show log-listing format
o
–L
show thread information
o
–a
exclude processes not associated with a terminal
o
–x
includes processes not attached to terminals
o
–f
prints process parentage
o
-- sort some
c
C
r
R
s
S
T
U
u
v
o
-o CODE prints custom information where CODE taken from the following list:
Code
%cpu
%mem
Bsdstart
bsdtime
comm.
Egid
egroup
etime
euid
euser
fgid
fname
fuid
fuser
label
lstart
lwp
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sorting options are:
cmd
simple name of executable
pcpu
cpu utilization
rss
resident set size
resident
resident pages
size
memory size in kilobytes
share
amount of shared pages
start_time
time process was started
uid
user ID number
user
user name
vsize
total VM size in kB
Header
%CPU
%MEM
START
TIME
COMMAND
EGID
EGROUP
ELAPSED
EUID
EUSER
FGID
COMMAND
FUID
FUSER
LABEL
STARTED
LWP
Description
cpu utilization of the process in "##.#" format. (alias pcpu)
physical memory in percentage. (alias pmem)
time the command started.
accumulated cpu time, user + system. "MMM:SS"
command name (only the executable name)
effective group ID number of the process (alias gid)
effective group ID of the process. (alias group)
elapsed time since the process was started, [[dd-]hh:]mm:ss.
effective user ID. (alias uid)
effective user name.
filesystem access group ID. (alias fsgid)
first 8 bytes of the base name of the proces executable file.
filesystem access user ID. (alias fsuid)
filesystem access user ID.
security label (used for SE Linux context data).
time the command started.
lwp (light weight process, or thread)
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![ps –eLf
# to show threads
ps –el
# to display long listing format
# To see every process with a user-defined format:
ps -eo pid,euser,ruser,lstart,stat,pcpu,pmem,rss,vsize --sort -rss
ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm.
ps -eo euser,ruser,suser,fuser,f,comm,label
# To get security info.
Sending Signals to Processes
•
kill [-signal] pid(s)
•
kill –l
the default signal is TERM (15)
lists the signals (for more info use man 7 signal)
# following commands send TERM signal (normal exiting)
kill 3453
kill -15 3453
kill –TERM 3453
# following commands send KILL signal (can be used if TERM failed)
kill –KILL 3453
kill -9 3453
Changing Process Scheduling Priority
•
nice [-n adj ] command where adj between -20 (highest) and 19 (lowest)
•
renice adj [[-p|-g] PID [[-u] user] for running processes
nice –n 10 myapp
renice -15 –p 201
# only superuser can increase priority
renice 15 –u john
# for all processes owned by john
Listing Background and Suspended Jobs
•
jobs
Resuming Suspended Jobs
•
bg [%job_number] or Ctl+Z brings the current process into background
•
fg [%job_number] brings the background process into foreground
You can use the following code example to test the commands:
(while true; do echo –n B >> file.log; sleep 1; done) &
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![Compound Commands
•
List of commands separated by semi-colons
•
Put the list between () to run them all in a subshell (treat it all as a one command)
date; who | wc –l >> mylogfile.txt
# only the second command will be logged
( date; who | wc –l) >> mylogfile.txt
# all output will be logged
Scheduling a Process
•
at time <commands> commands entered one per line, terminate with Ctl+D
•
atq [user] lists the current at jobs
•
atrm [user|atJobID]
removes at jobs
at 8:00pm December 7
at 7 am Thursday
at now + 5 minutes
at midnight + 23 minutes
Scheduling a Process Periodically
•
crontab used to install, deinstall or list the tables (crontabs).
-u user the user whose crontab is to be tweaked
-l
-r
remove the current crontab file
-e
•
display the current crontab file
edit. After exit from the editor, the modified crontab will be installed
Cronttab file:
o
Space delimited
o
Fields: minute, hour (0-23), day of month (0-31), month (1-12), and day of
week (0=Sun to 6).
Min
Hour
DoM
Month
DoW
3
4
*
*
1,3,5 find ~ -name core | xargs rm –f P{}
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Commands
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![Using Functions
•
functionname() { [return ...] }
•
Arguments passed to a function are accessed by its positional parameters $1, $2 … etc.
•
return keyword sets the special variable $?
•
Variables are made local in a function using local keyword.
#!/bin/bash
printname(){
local firstname=$1 lastname=$2
echo –e "Full name: $lastname $firstnamen"
return 1
}
printname Ahmed Baraka
retval=$?
echo "Returned value: $retval"
Exit Status
•
$? contains exit status of the most recently executed command.
•
It takes values 0 for success, 1-255 for failure
•
exit
sets an exist status in a script
Conditional Execution
•
<cmd1> && <cmd2>
execute cmd2 if cmd1 succeeds
•
<cmd1> || <cmd2>
execute cmd2 if cmd1 fails
ping -c1 -W2 pc1 &> /dev/null
> && echo "pc1 is up"
> || $(echo 'pc1 is unreachable'; exit 1)
Using the if Statement
if [ condition ]; then
…
elif [condition]; the
…
else
…
fi
if [ $retval != 0 ]; then
echo "There was an error running the application"
exit $retval
fi
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![Using the Case Statement
case variable in
pattern1)
<command>;;
pattern2)
<command>;;
esac
#!/bin/bash
. ~/lib/funcs
case $1 in
start)
start_func;;
stop)
stop_func;;
restart)
stop_func
start_func;;
status)
status_func;;
*)
echo "Use Command"
esac
Using the For Loop
for variable in list-of-vlaues
do
commands...
done
#!/bin/sh
echo "Please enter a list of numbers between 1 and 100. "
read NUMBERS
for NUM in $NUMBERS
do
if [ "$NUM" -lt 1 ] || [ "$NUM" -gt 100 ]; then
echo "Invalid Number ($NUM) - Must be between 1 and 100!"
else
echo "$NUM is valid."
fi
done
Using the While loop
while condition
do
commands...
done
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![#!/bin/sh
# Guess the number game.
ANSWER=5
CORRECT=false
# The correct answer
# The correct flag
while [ "$CORRECT" != "true" ]
do
# Ask the user for the number...
echo "Guess a number between 1 and 10. "
read NUM
# Validate the input...
if [ "$NUM" -lt 1 ] || [ "$NUM" -gt 10 ]; then
echo "The number must be between 1 and 10!"
elif [ "$NUM" -eq "$ANSWER" ]; then
echo "You got the answer correct!"
CORRECT=true
else
echo "Sorry, incorrect."
fi
done
(while true; do echo –n B >> file.log; sleep 1; done)
Disrupting Loops
•
continue
jump back to the initial condition
•
break
jump to the command past the done
File Tests
•
Common file tests are:
-e
-f
file exists and is a regular file
-d
file exists and is a directory
-x
file exists and is an executable
-h
file exists and is symbolic link
-r
file exists and is readable by you
-s
file exists and is not empty
-w
file exists and is writable by you
-O
file exists and is effectively owned by you
-G
•
file exists
file exists and is effectively owned by your group
help test for the complete list
if [ -f $HOME/lib/functions ]; then
...
fi
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Linux fundamentals commands
- 1. Linux Fundamentals by Commands and Examples version 1.0 Editor: Ahmed Baraka Document Purpose This document is edited to be a quick reference of Linux essential commands. It can be used by Linux beginners as a reminder of basic Linux commands usage. It cannot be used to learn Linux from scratch. The document is oriented based on the required task, the command(s) to do the task, basic syntax of the command, and examples. No explanation will be presented. Usage Terms • Anyone is authorized to copy this document to any means of storage and present it in any format to any individual or organization for non-commercial purpose free. • No individual or organization may use this document for commercial purpose without a written permission from the editor. • There is no warranty of any type for the code or information presented in this document. The editor is not responsible for any loses or damage resulted from using the information or executing the code in this document. • If any one wishes to correct a statement or a typing error or add a new piece of information, please send the request to info@ahmedbaraka.com . If the modification is acceptable, it will be added to the document, the version of the document will be incremented and the modifier name will be listed in the version history list. Page 1 Linux Fundamentals by Commands and Examples
- 2. Version History Version 1.0 Date Updates 25-June-2009 Initial document. Resources Resource Name Linux Essentials article by Thomas Girke. The Linux Cookbook: Tips and Techniques for Everyday Use by Michael Stutz Red Hat Linux Getting Started Guide, 2003 Red Hat Essentials RH033 (courseware material) Linux Reviews website The Linux Tutorial website Zytrax Info website Academic Computing And Communications Center ACCC website The Linux Information Project website UNIX & Linux Shell Scripting Tutorial website Page 2 Linux Fundamentals by Commands and Examples
- 3. Contents Introduction ___________________________________________ 7 Unix variants _______________________________________________7 GNU/Linux distributions ______________________________________7 Getting Started _________________________________________ 8 Virtual Consoles ____________________________________________8 Changing password __________________________________________8 Logging-In_________________________________________________8 Date and Time Commands _____________________________________8 Making Arithmetic Calculations _________________________________8 Generating Sequential Numbers ________________________________8 Getting Help _______________________________________________9 Handy shortcuts ____________________________________________9 Managing Files and Directories____________________________ 10 Files and Directories Commands _______________________________10 Determining File Content_____________________________________11 Viewing Files ______________________________________________11 Hard and Symbolic (Soft) Links________________________________12 Checking Free Space ________________________________________12 Searching Files By Names ____________________________________12 Searching Files By Names and Attributes ________________________12 Archiving Files _____________________________________________14 Compression Utilities _______________________________________14 Text File Processing Tools ____________________________________14 Users, Groups and Permissions ___________________________ 15 Change Password __________________________________________15 Change Your Identity _______________________________________15 User Information Commands _________________________________15 Changing File Ownership_____________________________________15 Changing Permissions _______________________________________15 Default File Permission ______________________________________15 Special Permission _________________________________________16 Page 3 Linux Fundamentals by Commands and Examples
- 4. bash Shell Basics ______________________________________ 17 File Blobbing ______________________________________________17 History Tricks _____________________________________________17 Command Line Expansion ____________________________________17 Local Shell Variables ________________________________________18 Aliases___________________________________________________19 Type ____________________________________________________19 Environment Variables ______________________________________19 Showing Path of Executable __________________________________19 Login and Non-Login Shells ___________________________________20 Startup and Logout Scripts ___________________________________20 Recording a Shell Session ____________________________________20 Standard I/O and Pipes _________________________________ 21 Redirecting Output to a File __________________________________21 Redirecting STDOUT to a Program (Piping)_______________________21 Redirecting to Multiple Targets ________________________________21 Redirecting STDIN from a File _________________________________21 Sending Multiple Lines to STDIN _______________________________21 Text Files and String Manipulation _________________________ 22 Viewing File Contents _______________________________________22 Viewing File Excerpts _______________________________________22 Extracting Text by Column ___________________________________22 Gathering Text Statistics _____________________________________22 Sorting Text_______________________________________________23 Eliminating Duplicates_______________________________________23 Comparing Files____________________________________________23 Spell Checking with aspell____________________________________23 Converting Characters_______________________________________24 Combining Files ____________________________________________24 Expanding Tabs Into Spaces __________________________________24 Regular Expressions ________________________________________24 Extended Regular Expressions ________________________________25 Extracting Text by Keyword __________________________________25 Search and Replace _________________________________________26 Page 4 Linux Fundamentals by Commands and Examples
- 5. Editing Text by Programming Language _________________________26 Using the Text Editor vi _________________________________ 27 Modes ___________________________________________________27 Search and Replace (Command Mode) __________________________27 Manipulating Text (Command Mode)____________________________27 Undoing Changes (Command Mode) ____________________________28 Visual Mode _______________________________________________28 Using Multiple "windows" ____________________________________28 Configuring vi and vim ______________________________________28 Managing Processes ____________________________________ 29 Listing Processes___________________________________________29 Sending Signals to Processes _________________________________31 Changing Process Scheduling Priority ___________________________31 Listing Background and Suspended Jobs_________________________31 Resuming Suspended Jobs ___________________________________31 Compound Commands _______________________________________32 Scheduling a Process________________________________________32 Scheduling a Process Periodically ______________________________32 bash Shell Scripting Basics _______________________________ 33 Creating Shell Scripts _______________________________________33 Handling Input ____________________________________________33 Shell Script Debugging ______________________________________33 Handling Positional Parameters (Arguments) _____________________33 Using Functions ____________________________________________34 Exit Status ________________________________________________34 Conditional Execution _______________________________________34 Using the if Statement_______________________________________34 Using the Case Statement ____________________________________35 Using the For Loop _________________________________________35 Using the While loop ________________________________________35 Disrupting Loops ___________________________________________36 File Tests _________________________________________________36 String Tests _______________________________________________37 Page 5 Linux Fundamentals by Commands and Examples
- 6. Shell Option Test ___________________________________________37 Logical Tests ______________________________________________37 Comparison _______________________________________________37 Page 6 Linux Fundamentals by Commands and Examples
- 7. Introduction Unix variants • Unix, GNU/Linux, Solaris, IRIX, HP-UX, FreeBSD, OpenBSD, NetBSD, Darwin (Mac), and more... GNU/Linux distributions • • Page 7 Ubuntu, Edubuntu, Debian, RedHat, Fedora, Slackware, SuSE, Darwin, and more... Family tree of the GNU/Linux distributions Linux Fundamentals by Commands and Examples
- 8. Getting Started Virtual Consoles • In Red Hat: available through CTRL+ALT+F[1-6] • If X is running, it is available as CTRL+ALT+F7 Changing password • passwd Logging-In • From Mac or LINUX ssh -X your_username@hostname • From Windows: Open Putty and select ssh. • Use WinSCP software for file exchange. Date and Time Commands • date u display date and time in UTC R display date and time in RFC822 (used in email messages) • chrony package maintains time by connecting to servers over the Internet. • cal output a calendar for the current month print calendar of current year y cal 2010 #output a calendar for the year 2010 Making Arithmetic Calculations • bc • supported operators: + - * / % ^ sqrt() Generating Sequential Numbers • seq w make all generated numbers of same width s 'b' make b character as the separator between numbers seq 7 seq -5 5 Page 8 Linux Fundamentals by Commands and Examples
- 9. seq 1 2 10 # from 1 to 10 increment by 2 seq −s ' ' 1 23 # separated by spaces Getting Help • man • info • apropos search for only • whatis to list a one−line description of a program • Software packages may store its help files in /usr/share/doc • Online help: SuperMan Pages, Linux Documentation Project (LDP) • LinuxQuestions.org exact matches man ls man –k copy # search for "copy" in the whatis database apropos copy # search for "copy" (not "xcopy") in the whatis database man –f copy # restrict search for the whole word ls -- help # brief help usage info cp # information is organized into sections whatis who Handy shortcuts # up(down)_key scrolls through command history # <something-incomplete> TAB completes path/file_name # Ctrl+a # cursor to beginning of command line # Ctrl+e # cursor to end of command line # Ctrl+d # delete character under cursor # Ctrl+k # cut line from cursor into kill buffer # Ctrl+y # paste content from Ctrl k Page 9 Linux Fundamentals by Commands and Examples
- 10. Managing Files and Directories Files and Directories Commands • pwd • cd • ls • File types that may be listed by ls –l : (see the options in the example below) - regular file d directory l symbolic link b block special file c character special file p named pipe s socket • cp • rm • mv • mkdir • rmdir • touch create empty files or update file timestamps • File Name Expansion characters can be used with these commands. # for copying between hosts, see next section cd .. # one level up cd # home directory cd - # previous directory ls –a # include hidden files ls –l # long listing ls –R # recurses through subdirectories with contents ls –d # directory names without their contents ls –lh # print sizes in human readable format ls –ld # avoid listing directory contents ls –i # print index number ls –S # sort by file size ls –t # sort by modification time (newest first) ls –r # reverse order while sorting ls –l --time-style=STYLE # STYLE: full-iso, long-iso, iso, locale, +FORMAT cp file1 file2 # timestamp changes for the new file Page 10 Linux Fundamentals by Commands and Examples
- 11. cp –p file1 file2 # all of the attributes are preserved cp file1 dir1 cp file1 file2 dir1 cp ./dir1/* dir2 cp –r dir1 dir2 # -r (same as -R) copy entire directory tree # links aren't copied, permissions aren't preserved cp –a dir1 dir2 # copy the entire tree including permissions and links mv file1 file2 # renames directories or files mv file1 ./dir1 # moves file/directory as specified in path rm file1 # removes file name rm -r dir1 # removes directory including its content, rm -rf dir # 'f' argument turns confirmation off rm -- -myfile # the fielename containes hyphen touch {doc,sheet}_{jan,feb,mar} touch file{0..6}.txt Determining File Content • file file myfile Viewing Files • cat • less • less navigation commands: space ahead one full screen ENTER ahead one line b back one full screen k back one line g top of the file G bottom of the file /text search forward for text (Regular Expressions can be used) n repeat last search N repeat backward last search q quit Page 11 Linux Fundamentals by Commands and Examples
- 12. Hard and Symbolic (Soft) Links • ln • ls –l in case of soft link, it displays the link name and the referenced file ln –s filename Checking Free Space • df space usage by file systems • du disk space by directories and subdirectories df –h # -h prints size in readable format du –h –s ~ # -s reports single directory summary Searching Files By Names • locate [options] name(s) • slocate [options] name(s) • Only the files you own are searched • Some options are shown in the example below. • locate.db or slocate.db databases are used • updatedb or locate -u to manually update the database locate "*.png" # wildcard characters can be used locate "*.png" -q # supress errors locate -n 15 "*.html" # only 15 resultes returned locate -i "*.HtmL" # case-insensitive search Searching Files By Names and Attributes • find <dirs> [conditions] [–exec cmd {} ;] -atime n File was last accessed n days ago -ctime n File was last changed n days ago -user uname File is owned by user uname (or user ID) -group gname File belongs to group gname (or group ID) -size n[cwbkMG]b 512-byte blocks (default), c in bytes, w two-byte words, k kilobyte -iname case -insensitive version of –name -o logical operator between criteria (by default it is AND) -not negate (logical NOT) -perm mode permission bits are exactly mode (octal or symbolic). -perm -mode ALL of the permission bits mode are set for the file. Page 12 Linux Fundamentals by Commands and Examples
- 13. Any of the permission bits mode are set for the file. -perm +mode -regex pattern Full path filename (not only filename) matches regular expression pattern. -mtime n Files was last modified Exactly n*24 hours ago. -mtime +n Files was last modified >= n*24 hours ago. -mtime -n Files was last modified <= n*24 hours ago. -mmin n Files was last modified n minutes ago. −daystart measure time in the options above from the beginning of the current day instead of 24 hours ago. -newer <file> Files newer than <file> modification date find . –name "*.html" find -iname snow.png find -user peter -group peter find -user joe -not -group joe find -user joe -o -user jane find -not ( -user joe -o -user jane ) find -perm 755 # matches if mode is exactly 755 find -perm +222 # matches if anyone can write find -perm -222 # matches if everyone can write find -perm -002 # matches if other can write find -size 1024k # excatly 1 MB find -size +1024k # over 1 MB find -size -1024k # less than 1 MB find ~ −empty # find empty regular files or directories find -size +102400k -ok gzip {} ; # OK prompte before acting find . -regex '.*[124].*ms$' find ~ −mtime 1 find ~ −mtime 1 # files modified exactly 24 hours ago −daystart # modified yesterday find ~ −mtime +356 # one year or longer ago find ~ −mtime 2 −mtime −4 −daystart # two to four days ago # files that were modified after May 4 of the current year touch −t 05040000 /tmp/timestamp find ~ −newer /tmp/timestamp Page 13 Linux Fundamentals by Commands and Examples
- 14. Archiving Files • tar cvf archive_name files … to create an archive file c create a new archivd v produces verbose messages f archive file name j use bzip2 compression z use gzip compression • tar tf archive_name to inspect files in an archive, if v option is used, long file list • tar xvf archive_name to extract an archive file (always to current directory) tar cvf mywork.tar .bas_profile /tmp tar cvf myHome.tar ~ Compression Utilities • gzip –v file(s) v option displays compression percentage, original file replaced only regular files are compressed • bzip2 –v file better compression • gunzip filename.gz uncompress the file • gzip –d filename.gz uncompress the file • gunzip –c filename.gz list contents of the compressed file in STDOUT, the file unchanged • bunzip2 –v file Text File Processing Tools • Check the section Text File Processing Tools Page 14 Linux Fundamentals by Commands and Examples
- 15. Users, Groups and Permissions Change Password • passwd Change Your Identity • su username • su - username # start a login shell User Information Commands • whoami # who you are • groups, id # what groups you belong to • users, who, w # who is logged on • last # login/reboot history Changing File Ownership • chown user_name file|directory • chgrp group_name file|directory chown john myfile chown –R john dir # operate on files and directories recursively Changing Permissions • chmod mode file where mode is: [u,g or o] [+ or -] [r, w or x] (Symbolic Method) where mode is: 4:r 2:w 1:x (Numeric Method) chmod o-rwx file1 chmod u-w,go-x file1 chmod +x file1 # the file is executable to all security levels chomod 775 file1 Default File Permission • umask Page 15 # if case of 0002, 664 permission for files, 775 for directories Linux Fundamentals by Commands and Examples
- 16. Special Permission • chmod Xnnn # X: 4 for suid, 2 for sgid, 1 for sticky bit • suid and sgid are effective on executable files: the program runs with permissions of the owner, not the executor. • sgid and sticky bit are effective on directories: o sticky bit: files in the directory can be deleted by the owner or the root, regardless of the directory write permission. o Sgid: files created in the directory will inherit its group affiliation from the directory, rather than the user. ls -l /usr/bin/passwd -r-s--x--x 1 root root ls -ld /tmp/ drwxrwxrwt 10 root root chmod 2770 GroupDir Page 16 Linux Fundamentals by Commands and Examples
- 17. bash Shell Basics File Blobbing * matches zero of more characters ? matches any single character [a-z] matches a range of characters [^a-z] matches all except the range ls file* ls ??file ls file[1-9] ls file[^6-0] History Tricks • history • Use the up and down keys to scroll through previous commands. • Type Ctrl-r to search for a command in command history. • Esc+. to recall last argument from previous command. • !n re-execute command number n Command Line Expansion • Command Expansion: $() or `` • Brace Expansion: { } • Arithmetic: $[] • Arithmetic Evaluations: + - * / ** % (Full list in Arithmetic Evaluation section in bash man page) • backslash makes the next character literal and can be used as last character on line to continue command on next line. • To pass special characters as a string: $'string' • Special backslash escape sequences: a Alert (rings the system bell). b Backspace. e Escape. f Form feed. n Newline. r Carriage return. t Horizontal tab. Page 17 Linux Fundamentals by Commands and Examples
- 18. v Backslash. NNN • Vertical tab. Character whose ASCII code is NNN in octal (base 8). Filename Expansion Characters: used with commands handling files and directories: * zero or more characters ? exactly one character [list] one character in the list. Examples: [abc],[a-m], a[-b]c [!list] except the characters in the list. For example: a[!b]c matches aac a-c adc, but not abc. echo "This system's name is $(hostname)" echo $'Note the space belown' # doesn't work if you use double quote echo current date is `date` echo file{1,3,5} echo Area: $[ $X * $Y ] # equivalent to $[$X*$Y] echo Your cost: $8.00 find / -name myfile* mv /usr/tmp/song[0−9].cdda ~/music Local Shell Variables • VARIABLE=value • echo $VARIABLE • To see list of the local variables that configure the shell, see the Shell Variables section of the bash man page. • Common Local Configuration Variables PS1 the prompt d date h short hostname t time u user name w current working directory ! history number of the current command $ o $ for superusers, # for non-privileged user o HISTFILESIZE how many commands to save in history o COLUMNS width of the terminal o LINES height of the terminal Page 18 Linux Fundamentals by Commands and Examples
- 19. • Common Local Information Variables o HOME user's home directory o EUID user's effective UID PS1="uw$" Aliases • alias alias lf="ls –Fca" alias rm="rm –i" rm –r myfile #to run the command, not the alias Type • to ask the shell what it is using to fulfill the command type type rm tyupe cate Environment Variables • export VARIABLE=value • Common Environment Variables: o user home directory path o LANG default language (like en_US.UTF-8) o PWD current working directory o EDITOR default editor used by programs o • HOME LESS options to pass to the less command reset when the screen become corrupted EDITOR=/usr/bin/vim; export EDITOR export EDITOR=/usr/bin/pico EDITOR= # once exported, no need to export it again to change its value Showing Path of Executable • which which xboard Page 19 Linux Fundamentals by Commands and Examples
- 20. Login and Non-Login Shells • Login shells are: o • Any shell created at login (includes X login) o su - Non-login shells are: o su o graphical terminals o executed scripts o any other bash instances Startup and Logout Scripts • Login Sells /etc/profile /etc/profile.d ~/.bash_profile ~/.bashrc /etc/bashrc • Non-Login Shells ~/.bashrc /etc/bashrc /etc/profile.d • Logout Script ~/.bash_logout Recording a Shell Session • script <filename> • exit Page 20 record session typescript records in filename end session recording Linux Fundamentals by Commands and Examples
- 21. Standard I/O and Pipes Redirecting Output to a File • > Redirect STDOUT to file (overwrite) • >> Redirect STDOUT to file (append) • 2> Redirect STDERR to file • &> Redirect all output to file • 2>&1: Redirects STDERR to STDOUT • (): Combines STDOUTs of multiple programs find /etc -name passwd > find.out 2> find.err find /etc -name passwd &> find.all ( cal 2007 ; cal 2008 ) Redirecting STDOUT to a Program (Piping) • Pipes (the | character) can connect commands ls -l /etc | less Redirecting to Multiple Targets • tee - read from standard input and write to standard output and files • command1 | tee filename | command2 store STDOUT of command1 in filename, then pipes to command2 find /etc -name "r*" | tee foundlist.txt | less Redirecting STDIN from a File • Redirect standard input with < $ tr 'A-Z' 'a-z' < myfile # equivalent to cat myfile | tr 'A-Z' 'a-z' Sending Multiple Lines to STDIN • Redirect multiple lines from keyboard to STDIN with <<WORD • All text until WORD is sent to STDIN $ mail -s "Please Call" test@mydomain.com <<END Page 21 Linux Fundamentals by Commands and Examples
- 22. Text Files and String Manipulation Viewing File Contents • cat dump one or more files to STDOUT • less view file or STDIN one page at a time • less navigation commands: space ahead one full screen ENTER ahead one line b back one full screen k back one line g top of the file G bottom of the file /text search forward for text n repeat last search N repeat backward last search q quit Viewing File Excerpts • head • tail head -n 5 .bash_profile tail -n 5 .bash_profile tail -n 5 -f mylogfile # follow subsequent additions to the file # useful for monitoring log files! Extracting Text by Column • cut -d -f -c to specify the column delimiter (default is TAB) to specify the column to print to cut by characters cut -d: -f1 /etc/passwd grep root /etc/passwd | cut -d: -f7 cut -c2-5 /usr/share/dict/words Gathering Text Statistics • wc -l for only line count -w for only word count Page 22 Linux Fundamentals by Commands and Examples
- 23. -c for only byte count -m for character count wc story.txt # words, lines, bytes 39 237 1901 story.txt Sorting Text • sort -r -n -f -u -t c -k X performs a reverse (descending) sort performs a numeric sort ignores (folds) case of characters in strings (unique) removes duplicate lines in output uses c as a field separator sorts by c-delimited field X grep bash /etc/passwd | sort sort –t : -k 3 –n /etc/passwd # sort by uid Eliminating Duplicates • sort -u: removes duplicate lines from input • uniq: removes duplicate adjacent lines -c prefix lines by the number of occurrences -d only print duplicate lines -u only print unique lines cut –d: -f7 /etc/passwd | sort | uniq Comparing Files • diff diff file1 file2 Spell Checking with aspell • aspell aspell check letter.txt aspell list < letter.txt aspell list < letter.txt | wc -l Page 23 Linux Fundamentals by Commands and Examples
- 24. Converting Characters • tr converts characters in one set to corresponding characters in another set tr 'a-z' 'A-Z' < lowercase.txt Combining Files • paste combines files horizontally and separate the pasted lines by TAB by default. paste –d: ids.txt names.txt > merged.txt # separate the data with colon Expanding Tabs Into Spaces • expand convert the tabs in the file to spaces expand tabfile.txt > tabfile.expanded.txt Regular Expressions • Wildcard Characters another single character . any single character [abc] any single character in the set [a-c] any single character in the range [^abc] any single character not in the set [^a-c] any single character not in the range • Modifiers number of the previous character * zero or more of the previous char + one or more of the previous char ? zero or one of pervious char {i} exactly i of the previous char {i,} i or more of the previous char {i,j} i to j of the previous char • Anchors match the beginning or end of a line or word ^ line begins with $ word begins with > • line ends with < word ends with Other expressions [:alnum:] Alpha-numeric characters 0 to 9 OR A to Z or a to z [:alpha:] Control characters [:digit:] Page 24 Alpha character a-z A-Z [:cntrl:] Digits 0 to 9 Linux Fundamentals by Commands and Examples
- 25. [:graph:] Graphics characters [:print:] Printable characters [:punct:] Punctuation " ' ? ! ; : # $ % & ( ) * + - / < > = @ [ ] ^ _ { } | ~ [:space:] White spaces (space, tab, NL, FF, VT, CR) [:blank:] Space and Tab characters only ^S[^ ]* R # the last name begins with S and first name begins with R. ^[M-Z].*[12] # the last name begins with a letter from M to Z and where the # phone number ends with a 1 or 2. '^..$' # any word of only two characters '^.{17}$' # words of exactly seventeen characters wide [0-9]{5,10} # all number combinations between 5 and 10 number long [a-z])$ # The is an escape characher (.*l # contains ls and preceeded by an open bracket Extended Regular Expressions • Except word anchors, basic regular expressions requiring a preceding backslash do not require backslash • Used by: o egrep o grep –E o awk Extracting Text by Keyword • grep [OPTION]... PATTERN [FILE] ... -i -n -v -AX -BX to to to to to search case-insensitively print line numbers of matches print lines not containing pattern include the X lines after each match include the X lines before each match • grep uses by default basic Regular Expressions • egrep uses Extended Regular Expressions grep 'root' file*.doc # this will list the file name grep –h 'root' file*.doc # to avoid listing the file names grep 'ahmed' /etc/passwd # highly advisable to use sing quote date --help | grep year egrep 'a{2,5}' myfile # search for counter 2,3,4 or 5 letter a's egrep '<bye>' myfile Page 25 Linux Fundamentals by Commands and Examples
- 26. Search and Replace • sed (stream editor) uses regular expressions in search string (but not in replace) sed 's/cat/dog/' petsfile # makes the replacement once per line sed 's/cat/dog/g' petsfile # multiple changes per line sed 's/[Cc]at/dog/g' petsfile sed 's/<[Cc]at>/dog/g' petsfile # search by word (not string) sed 's/<[Cc]at>/& and dog/g' petsfile # whatever found (Cat or cat), it will # be replaced with cat and dog sed '10,40s/cat/dog/g' petsfile # only lines from 10 and 40 searched sed '/begin/,/end/s/cat/dog/' petfiel # search will start from the line # containing "begin" to the line # containing "end" sed –e 's/cat/dog/g' –e 's/cow/goat/g' petsfile # multiple find and replaces Editing Text by awk • awk • All extended regular expressions work except curly brace counters. To use them, use -posix or --re-interval options. awk ' { print } ' myfile # equivalent to cat command awk '/bye/ { print } ' myfile # print lines containing the pattern awk '/[2-5]+/ { print } ' myfile awk ' { print $2, $1 } ' myfile awk ' { print $2 " Page 26 # print fields 2 and 1 in a space separated # text file. " $1 } ' myfile # in a tab separated file Linux Fundamentals by Commands and Examples
- 27. Using the Text Editor vi Modes Command Mode o Default mode of vim o Move by character: Arrow Keys, h, j, k, l o Move by word: w, b o Move by sentence: ), ( o Move by paragraph: }, { o Jump to line x: xG o Jump to end: G Insert mode o i begins insert mode at the cursor o A append to end of line o I insert at beginning of line o o insert new a line (below) o O insert new line (above Ex Mode o :w writes (saves) the file to disk o :wq writes and quits o :q! quits, even if changes are lost Search and Replace (Command Mode) • /, n, N Search • <>/<>/<> Search/Replace (as in sed command) :1,5s/cat/dog/g # search in lines 1 to 5 and replace all words in any line :%s/cat/dog/gi # the whole file Manipulating Text (Command Mode) Action followed by Target Possible actions: • change (c) • cut (d) • yank (y) • paste (p) without target Page 27 Linux Fundamentals by Commands and Examples
- 28. Possible target: • Line as in action • Letter l • Word w • Sentence ahead ) • Sentence behind ( • Paragraph above { • Paragraph below } Undoing Changes (Command Mode) • u undo most recent change. • U undo all changes to the current line since the cursor landed on the line. • Ctrl-r redo last "undone" change Visual Mode • Allows selection of blocks of text • v starts character-oriented highlighting • V starts line-oriented highlighting • Highlighted text can be deleted, yanked, changed, filtered, search/replaced, etc. Using Multiple "windows" • Multiple documents can be viewed in a single vim screen. • Ctrl-w, s splits the screen horizontally • Ctrl-w, v splits the screen vertically • Ctrl-w, Arrow moves between windows • :q • Ex-mode instructions always affect the current window close the current window Configuring vi and vim • :set or :set all Configuring on the fly • ~/.vimrc or ~/.exrc Configuring permanently • :set showmode show when you are in insert mode • :set ic ignore case when searching • :set noic turn ignore case off • :set nu turn on line numbering • :set nonu turn line numbering off Page 28 Linux Fundamentals by Commands and Examples
- 29. Managing Processes Listing Processes • top continuously updated list • ps shows processes from the current terminal by default o -a all processes except session leaders and processes not associated with a terminal. o -A prints all processes. Identical to -e. o -e prints all processes. Identical to -A. o -H show process hierarchy o –u prints process owner information o –l show log-listing format o –L show thread information o –a exclude processes not associated with a terminal o –x includes processes not attached to terminals o –f prints process parentage o -- sort some c C r R s S T U u v o -o CODE prints custom information where CODE taken from the following list: Code %cpu %mem Bsdstart bsdtime comm. Egid egroup etime euid euser fgid fname fuid fuser label lstart lwp Page 29 sorting options are: cmd simple name of executable pcpu cpu utilization rss resident set size resident resident pages size memory size in kilobytes share amount of shared pages start_time time process was started uid user ID number user user name vsize total VM size in kB Header %CPU %MEM START TIME COMMAND EGID EGROUP ELAPSED EUID EUSER FGID COMMAND FUID FUSER LABEL STARTED LWP Description cpu utilization of the process in "##.#" format. (alias pcpu) physical memory in percentage. (alias pmem) time the command started. accumulated cpu time, user + system. "MMM:SS" command name (only the executable name) effective group ID number of the process (alias gid) effective group ID of the process. (alias group) elapsed time since the process was started, [[dd-]hh:]mm:ss. effective user ID. (alias uid) effective user name. filesystem access group ID. (alias fsgid) first 8 bytes of the base name of the proces executable file. filesystem access user ID. (alias fsuid) filesystem access user ID. security label (used for SE Linux context data). time the command started. lwp (light weight process, or thread) Linux Fundamentals by Commands and Examples
- 30. ni NI nlwp pgid PGID NLWP process pid ppid psr rgid rss PID process PPID PSR RGID RSS ruid ruser s RUID RUSER S sched sess sig sigcatch sigignore sigmask start_time stat suid suser time tname tt tty vsize vsz SCH SESS PENDING CAUGHT IGNORED BLOCKED START STAT SUID SUSER TIME TTY TT TT VSZ VSZ ID of the lwp being reported. (alias spid, tid) nice value. This ranges from 19 (nicest) to -20 (not nice to others) (alias nice) number of lwps (threads) in the process. (alias thcount) group ID or, equivalently, the process ID of the process group leader. (alias pgrp) ID number of the process. parent process ID. processor that process is currently assigned to. real group ID. resident set size, the non-swapped physical memory that a task has used (in kiloBytes). (alias rssize, rsz). real user ID. real user ID ( textual, if possible) minimal state display (one character). See sub-section below (alias state ) scheduling policy of the process (0,1,2) session ID (alias session, sid). pending. (alias pending, sig_pend). caught. (alias caught, sig_catch). ignored. (alias ignored, sig_ignore). blocked. (alias blocked, sig_block). starting time or date of the process. multi-character process state. saved user ID. (alias svuid). saved user name ( textual, if possible) (alias svuser). cumulative CPU time controlling tty (terminal). (alias tt, tty). controlling tty (terminal). (alias tname, tty). controlling tty (terminal). (alias tname, tt). virtual memory usage of entire process. see vsize. (alias vsize). Process statuses: R Runnable: executing S Sleeping: waiting for an event to occur to wake up T Stopped: not executing D Uninterruptible sleep Z Zombie: just before a process dies. It no notification acknowledgment received from parent, all resources except PID are released. When the stat keyword is used, additional characters may be displayed: < high-priority (not nice to other users) N low-priority (nice to other users) L has pages locked into memory (for real-time and custom IO) s is a session leader l is multi-threaded + is in the foreground process group ps aux # commonly used and equivalent to -aux ps –e # to see every process on the system ps –ef # to see every process on the system ps –eH # to print a process tree Page 30 Linux Fundamentals by Commands and Examples
- 31. ps –eLf # to show threads ps –el # to display long listing format # To see every process with a user-defined format: ps -eo pid,euser,ruser,lstart,stat,pcpu,pmem,rss,vsize --sort -rss ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm. ps -eo euser,ruser,suser,fuser,f,comm,label # To get security info. Sending Signals to Processes • kill [-signal] pid(s) • kill –l the default signal is TERM (15) lists the signals (for more info use man 7 signal) # following commands send TERM signal (normal exiting) kill 3453 kill -15 3453 kill –TERM 3453 # following commands send KILL signal (can be used if TERM failed) kill –KILL 3453 kill -9 3453 Changing Process Scheduling Priority • nice [-n adj ] command where adj between -20 (highest) and 19 (lowest) • renice adj [[-p|-g] PID [[-u] user] for running processes nice –n 10 myapp renice -15 –p 201 # only superuser can increase priority renice 15 –u john # for all processes owned by john Listing Background and Suspended Jobs • jobs Resuming Suspended Jobs • bg [%job_number] or Ctl+Z brings the current process into background • fg [%job_number] brings the background process into foreground You can use the following code example to test the commands: (while true; do echo –n B >> file.log; sleep 1; done) & Page 31 Linux Fundamentals by Commands and Examples
- 32. Compound Commands • List of commands separated by semi-colons • Put the list between () to run them all in a subshell (treat it all as a one command) date; who | wc –l >> mylogfile.txt # only the second command will be logged ( date; who | wc –l) >> mylogfile.txt # all output will be logged Scheduling a Process • at time <commands> commands entered one per line, terminate with Ctl+D • atq [user] lists the current at jobs • atrm [user|atJobID] removes at jobs at 8:00pm December 7 at 7 am Thursday at now + 5 minutes at midnight + 23 minutes Scheduling a Process Periodically • crontab used to install, deinstall or list the tables (crontabs). -u user the user whose crontab is to be tweaked -l -r remove the current crontab file -e • display the current crontab file edit. After exit from the editor, the modified crontab will be installed Cronttab file: o Space delimited o Fields: minute, hour (0-23), day of month (0-31), month (1-12), and day of week (0=Sun to 6). Min Hour DoM Month DoW 3 4 * * 1,3,5 find ~ -name core | xargs rm –f P{} Page 32 Commands Linux Fundamentals by Commands and Examples
- 33. bash Shell Scripting Basics Creating Shell Scripts • First line contains the magic "shbang" #!/bin/bash • Comments start with # • One command spans multiple lines with • By convenient, they have sh extension Handling Input • read assigns an input word(s) to a shell variable • words are separated by default with space. IFS variable controls the separator. #!/bin/bash read –p "Enter the words:" word1 word2 word3 echo "Word1 : $word1" echo "Word2 : $word2" echo "Word3 : $word3" Shell Script Debugging • Modify the shebang as follows #!/bin/bash –x #!/bin/bash -v • Alternatively, Invoke the shell interpreter with debug options bash –x scriptname bash –v scriptname Handling Positional Parameters (Arguments) • accessed by $1, $2, …, $9, ${10},${11},… • $0 reserved for the program name • $* holds all command line parameters • $# holds number of command line parameters #!/bin/bash printf "First Parameter :%sn" $1 printf "Second Parameter :%sn" $2 echo –e "nAll Page 33 Parameters: $*n" # -e option enables interpretation of the # backslash-escaped characters Linux Fundamentals by Commands and Examples
- 34. Using Functions • functionname() { [return ...] } • Arguments passed to a function are accessed by its positional parameters $1, $2 … etc. • return keyword sets the special variable $? • Variables are made local in a function using local keyword. #!/bin/bash printname(){ local firstname=$1 lastname=$2 echo –e "Full name: $lastname $firstnamen" return 1 } printname Ahmed Baraka retval=$? echo "Returned value: $retval" Exit Status • $? contains exit status of the most recently executed command. • It takes values 0 for success, 1-255 for failure • exit sets an exist status in a script Conditional Execution • <cmd1> && <cmd2> execute cmd2 if cmd1 succeeds • <cmd1> || <cmd2> execute cmd2 if cmd1 fails ping -c1 -W2 pc1 &> /dev/null > && echo "pc1 is up" > || $(echo 'pc1 is unreachable'; exit 1) Using the if Statement if [ condition ]; then … elif [condition]; the … else … fi if [ $retval != 0 ]; then echo "There was an error running the application" exit $retval fi Page 34 Linux Fundamentals by Commands and Examples
- 35. Using the Case Statement case variable in pattern1) <command>;; pattern2) <command>;; esac #!/bin/bash . ~/lib/funcs case $1 in start) start_func;; stop) stop_func;; restart) stop_func start_func;; status) status_func;; *) echo "Use Command" esac Using the For Loop for variable in list-of-vlaues do commands... done #!/bin/sh echo "Please enter a list of numbers between 1 and 100. " read NUMBERS for NUM in $NUMBERS do if [ "$NUM" -lt 1 ] || [ "$NUM" -gt 100 ]; then echo "Invalid Number ($NUM) - Must be between 1 and 100!" else echo "$NUM is valid." fi done Using the While loop while condition do commands... done Page 35 Linux Fundamentals by Commands and Examples
- 36. #!/bin/sh # Guess the number game. ANSWER=5 CORRECT=false # The correct answer # The correct flag while [ "$CORRECT" != "true" ] do # Ask the user for the number... echo "Guess a number between 1 and 10. " read NUM # Validate the input... if [ "$NUM" -lt 1 ] || [ "$NUM" -gt 10 ]; then echo "The number must be between 1 and 10!" elif [ "$NUM" -eq "$ANSWER" ]; then echo "You got the answer correct!" CORRECT=true else echo "Sorry, incorrect." fi done (while true; do echo –n B >> file.log; sleep 1; done) Disrupting Loops • continue jump back to the initial condition • break jump to the command past the done File Tests • Common file tests are: -e -f file exists and is a regular file -d file exists and is a directory -x file exists and is an executable -h file exists and is symbolic link -r file exists and is readable by you -s file exists and is not empty -w file exists and is writable by you -O file exists and is effectively owned by you -G • file exists file exists and is effectively owned by your group help test for the complete list if [ -f $HOME/lib/functions ]; then ... fi Page 36 Linux Fundamentals by Commands and Examples
- 37. String Tests • String operators: -z STRING True if string is empty. -n STRING True if string is not empty. STRING1 = STRING2 True if the strings are equal. STRING1 != STRING2 True if the strings are not equal. STRING1 < STRING2 True if STRING1 sorts before STRING2 lexicographically. STRING1 > STRING2 True if STRING1 sorts after STRING2 lexicographically. Shell Option Test • Shell option operator True if the shell option OPTION is enabled. -o OPTION Logical Tests • Logical Operators ! EXPR True if expr is false. EXPR1 -a EXPR2 True if both expr1 AND expr2 are true. EXPR1 -o EXPR2 True if either expr1 OR expr2 is true. Comparison • Comparison Operators arg1 OP arg2 Page 37 OP is one of: -eq, -ne, -lt, -le, -gt, or -ge. Linux Fundamentals by Commands and Examples