Unix Commands and Shells Scripts in OS.pptx

Darshan Institute of Engineering &
Technology, Rajkot
Unit - 9
Unix Commands
maulik.trivedi@darshan.ac.in
9998 265 805
Computer Engineering Department
Prof. Maulik D. Trivedi
Operating System (OS)
GTU # 3140702

✓ Loopin
g
Outline
• What is an Operating System (OS) ?
• Tasks of Operating System
• What is Unix?
• Unix Operating System
• Unix History
• Features of Unix
• What is shell?
• Linux Operating System
• Architecture
• Component of Linux System
• Basic Function of Kernel
• Directory Structure
• Linux Vs. Windows

Prof. Maulik D Trivedi
#3140702 (OS) ⬥ Unit 9 – Unix/Linux Operating
4
cd (Change Directory) Command
🞂 The cd command is used to change the current directory (i.e., the directory in
which the user is currently working)
🞂 Syntax :
cd [-Options] [Directory]
🞂 Example :
Option Use
cd .. Change Current directory to parent directory
cd ~ Move to users home directory from anywhere
cd lab_1 Change from current working directory to lab_1
cd ../downloads
If we are currently in /home/username/documents then we
would be placed in /home/username/downloads.

5
cd Command Example
cd .. Change Current directory to parent directory

6
cd Command Example
cd ~ Move to users home directory from anywhere

7
cd Command Example
cd
lab_1
Change from current working directory to lab_1

8
cd Command Example
cd
../downloads
If we are currently in
/home/student/documents then we would be
placed in /home/student/downloads

9
ls Command
🞂 List directory contents.
🞂 Syntax :
ls [Options] [file|dir]
🞂 Example :
Option Use
ls -l
To show long listing information about the
file/directory
ls -a List all files including hidden file starting with '.'
ls -r List in reverse order
ls -t Sort by time & date
ls -s Sort by file size

10
🞂 Directory & Files
🞂 A read, write, execute permissions for user(root), group and others respectively
🞂 A number of links for file / dir.
🞂 It specifies owner of the file / dir.
🞂 It specifies group of the file / dir.
🞂 It indicates the file / dir size in bytes.
🞂 It specifies the date and time of the last modification of the file.
🞂 It specify name of the file / dir.
ls Command
drwxr-
xr-x
own
er
grou
p
othe
rs

11
ls Command Example
ls -l
To show long listing information about the
file/directory

12
ls Command Example
ls -a
List all files including hidden file starting
with '.'

13
ls Command Example
ls -r List in reverse order

14
man Command
• It is the interface used to view the system's reference manuals.
🞂 Syntax :
man [command name]
🞂 Example

15
echo Command
🞂 Display a line of text/string on standard output or a file.
🞂 Syntax :
echo [option] [string]
🞂 Example :
Option Use
echo -n Do not output a trailing newline
echo -e
Enable interpretation of backslash escape
sequences
Option Use
b It removes all the spaces in between the text
n It creates new line from where it is used
t It create horizontal tab spaces

16
echo Command Example
echo -n Do not output a trailing newline

17
echo Command Example
b It removes all the spaces in between the text
n It creates new line from where it is used
t It create horizontal tab spaces
echo -e
Enable interpretation of backslash escape
sequences

18
cal Command
🞂 Displays a simple, formatted calendar in your terminal.
🞂 Syntax :
cal [options] [[[day] month] year]
🞂 Example :
Option Use
cal -1 Display single month output. (This is the default.)
cal -3 Display three months spanning the date.
cal -s Display Sunday as the first day of the week.
cal -m Display Monday as the first day of the week.
cal -j
Use day-of-year numbering for all calendars. These are also
called ordinal days. Ordinal days range from 1 to 366.
cal –y Display a calendar for the whole year

19
cal Command Example
Cal or cal -1 Display single month output. (This is the default.)

20
cal Command Example
cal -3 Display three months spanning the date.

21
cal Command Example
cal -s Display Sunday as the first day of the week.

22
cal Command Example
cal -m Display Monday as the first day of the week.

23
cal Command Example
cal -j
Use day-of-year numbering for all calendars. These are
also called ordinal days. Ordinal days range from 1 to
366.

24
cal Command Example
cal –y Display a calendar for the whole year

25
date Command
🞂 Print or set the system date and time.
🞂 Syntax :
date [OPTION]... [+FORMAT]
🞂 Example :
Option Use
date +%a The abbreviated weekday name (e.g., Sun)
date +%A The full weekday name (e.g., Sunday)
date +%b The abbreviated month name (e.g., Jan)
date +%B Locale's full month name (e.g., January)
date +%C
The current century; like %Y, except omit last two
digits (e.g., 20)
date +%w day of week (0..6); 0 is Sunday

26
date Command
Option Use
date +%d Display the day of the month
date +%m Displays the month of year (01 to 12)
date +%y Displays last two digits of the year(00 to 99)
date +%Y Display four-digit year.
date +%T Display the time in 24 hour format as HH:MM:SS
date +%H Display the hour
date +%M Display the minute
date +%S Display the seconds
date +%V
ISO week number, with Monday as first day of
week (01..53)
date +%P locale's equivalent of either AM or PM

27
date Command Example
date +%a The abbreviated weekday name (e.g., Sun)
date +%A The full weekday name (e.g., Sunday)

28
date +%b The abbreviated month name (e.g., Jan)
date +%B Locale's full month name (e.g., January)

29
date +%c Full date with IST timing
date +%C
The current century; like %Y, except omit last
two digits (e.g., 20)

30
date +%d Display the day of the month
date +%m Displays the month of year (01 to 12)

31
date +%Y Display four-digit year.

32
date +%T
Display the time in 24 hour format as
HH:MM:SS
date +%H Display the hour
date +%M Display the minute
date +%S Display the seconds

33
date +%V
ISO week number, with Monday as first day of
week (01..53)

34
date +%P locale's equivalent of either AM or PM

35
clear Command
🞂 Clear the terminal screen.
🞂 If you take a detailed look after running the clear command, you'll find that it
doesn't really clear the terminal. The tool just shifts the text upwards, out of the
viewable area.
🞂 Syntax :
clear

36
clear Command Example

37
cat Command
• It is used to create, display and concatenate file contents.
🞂 Syntax :
cat [OPTION] [FILE]
🞂 Example :
Option Use
cat -b Omits line numbers for blank space in the output
cat -E Displays a $ (dollar sign) at the end of each line
cat -n Line numbers for all the output lines
cat -s Suppress repeated empty output lines
cat -T Displays the tab characters as ^I in the output

38
cat Command
🞂 Example :
$ cat > file1.txt
🞂 It creates file1.txt and allow us to insert content for this file.
🞂 After inserting content you can use ctrl+c to exit the file.
$cat file.txt > newfile.txt
🞂 Read the contents of file.txt and write them to newfile.txt, overwriting anything
newfile.txt previously contained. If newfile.txt does not exist, it will be created.
$cat file.txt >> newfile.txt
🞂 Read the contents of file.txt and append them to the end of newfile.txt.
If newfile.txt does not exist, it will be created.

39
cat Command
🞂 Example :
cat file1.txt file2.txt
• It will read the contents of file1.txt and file2.txt and display the result in the
terminal.
cat file1.txt file2.txt > combinedfile.txt
• It will concatenate the contents of file1.txt and file2.txt and write them to a new
file combinedfile.txt using the (>) operator.
• If the combinedfile.txt file doesn’t exist the command will create it. Otherwise it
will overwrite the file.

40
cat Command Example
🞂 $ cat > file1.txt
• It creates file1.txt and allow us to insert content for this file.
• After inserting content you can use ctrl+c to exit the file.

41
cat Command Example
cat -b Omits line numbers for blank space in the output
cat -E Displays a $ (dollar sign) at the end of each line

42
cat Command Example
🞂 $cat file.txt > newfile.txt
• Read the contents of file.txt and write them to newfile.txt, overwriting anything
newfile.txt previously contained.
• If newfile.txt does not exist, it will be created.

43
cat Command Example
🞂 $cat file.txt >> newfile.txt
• Read the contents of file.txt and append them to the end of newfile.txt.
If newfile.txt does not exist, it will be created.

44
cat Command Example
🞂 cat file1.txt file2.txt
• It will read the contents of file1.txt and file2.txt and display the result in the
terminal.

45
cat Command Example
🞂 cat file1.txt file2.txt > combinedfile.txt
• It will concatenate the contents of file1.txt and file2.txt and write them to a new
file combinedfile.txt using the (>) operator.
• If the combinedfile.txt file doesn’t exist the command will create it otherwise it
will overwrite the file.

46
pwd (Print working directory) Command
• It prints the current working directory name with the complete path starting
from root (/).
🞂 Syntax :
pwd [-OPTION]
🞂 Example :

47
who Command
• It display the users that are currently logged into your Unix computer system.
🞂 Syntax :
who [-options] [filename]
🞂 Example :
Optio
n
Use
who -b Display the time of the last system boot
who -H Print a line of column headings
who -q
Displays all login names, and a count of all logged-on
users
who -a Display all details of current logged in user

48
who Command Example
who -b Display the time of the last system boot

49
who Command Example
who -H Print a line of column headings

50
who Command Example
who -q
Displays all login names, and a count of all logged-on
users

51
who Command Example
who -a Display all details of current logged in user

52
whoami Command
• This command prints the username associated with the current effective user
ID.
🞂 Syntax :
whoami [-OPTION]
🞂 Example :
Option Use
whoami --help Display a help message, and exit
whoami --
version
Display version information, and exit

53
whoami Command Example
whoami --help Display a help message, and exit

54
whoami Command Example
whoami --
version
Display version information, and exit

55
uname (unix name) Command
• Print information about the current system.
🞂 Syntax :
uname [-OPTION]
🞂 Example :
Option Use
uname -s Print the kernel name
uname -
n
Print the network node hostname
uname -v Print the kernel version
uname -
m
Print the machine hardware name
uname -
o
Print the operating system

56
uname Command Example
uname -
s
Print the kernel name

57
uname -
n
Print the network node hostname

58
uname -
v
Print the kernel version

59
uname -
m
Print the machine hardware name

60
uname -
o
Print the operating system

61
passwd Command
• The passwd command is used to change the password of a user account.
🞂 Syntax :
passwd [-options] [username]
🞂 Example :

62
mkdir Command
• This command is used to make Directories.
🞂 Syntax :
mkdir [-OPTION] DIRECTORY
🞂 Example :
Option Use
mkdir -v Print a message for each created directory
mkdir -p No error if existing, make parent directories as needed
mkdir -
m
To control the permissions of new directories

63
mkdir Command Example
mkdir -v Print a message for each created directory

64
mkdir -p No error if existing, make parent directories as needed

65
mkdir -m To control the permissions of new directories

66
rmdir Command
• This command removes empty directories from your filesystem.
🞂 Syntax :
rmdir [-OPTION] DIRECTORY
🞂 Example :
Option Use
rmdir -p
Remove directory and its ancestors… e.g., ‘rmdir -p
a/b/c’ is similar to ‘rmdir a/b/c a/b a’

67
rmdir Command Example
rmdir -
p
Remove directory and its ancestors…
e.g., ‘rmdir -p a/b/c’ is similar to ‘rmdir a/b/c a/b a’

68
cp(copy) Command
• This command is used to copy files and directories.
🞂 Syntax :
cp [option] source destination/directory
🞂 Example :
Option Use
cp -i Interactive - ask before overwrite
cp -f Force copy by removing the destination file if needed
cp -n Do not overwrite an existing file
cp -u Update - copy when source is newer than destination
cp -s Make symbolic links instead of copying
cp -R Copy directories recursively
cp -v Print informative messages

69
cp Command Example

70
cp Command Example
cp -i Interactive - ask before overwrite

71
cp Command Example
cp -v Print informative messages

72
cp Command Example
cp -s Make symbolic links instead of copying

73
mv(move) Command
• mv command is used to move files and directories.
🞂 Syntax :
mv [-options] source dest
🞂 Example :
Optio
n
Use
mv -i Interactive prompt before overwrite
mv -f Force move by overwriting destination file without prompt
mv -n Never overwrite any existing file
mv -u Update - move when source is newer than destination
mv -v Print informative messages

74
mv Command Example

75
rm(remove) Command
• The ‘rm’ command is used to delete files and directories.
🞂 Syntax :
rm [-OPTION] Filename
🞂 Example :
Optio
n
Use
rm -i Prompt before every removal
rm -d Delete a empty directory
rm -r Remove directories and their contents recursively
rm -f To remove the file forcefully

76
rm Command Example
rm -i Prompt before every removal

77
cut Command
• The cut command extracts a given number of characters or columns from a file.
🞂 Syntax :
cut [-options] [file]
🞂 Example :
Optio
n
Use
cut -c
Select only the characters from each line as specified in
LIST
cut -b Select only the bytes from each line as specified in LIST
cut -f
Cuts the input file using list of field. The default field to be
used TAB. The default behavior can be overwritten by
use of -d option
cut -d
Specifies a delimiter to by used as a field. Default field is
TAB and this option overwrites this default behavior

78
cut Command Example
cut -c
Select only the characters from each line as specified
in LIST

79
cut Command Example
cut -b Select only the bytes from each line as specified in LIST

80
cut Command Example
cut -f
Cuts the input file using list of field. The default field to be used TAB. The
default behavior can be overwritten by use of -d option
cut -d
Specifies a delimiter to by used as a field. Default field is TAB and this
option overwrites this default behavior

81
paste Command
• The paste command displays the corresponding lines of multiple files side-by-
side.
🞂 Syntax :
paste [-options] [file]
🞂 Example :
Optio
n
Use
paste -
d
Reuse characters from LIST instead of tabs
paste -
s
Paste one file at a time instead of in parallel

82
paste Command Example
paste -
d
Reuse characters from LIST instead
of tabs

83
paste Command Example
paste
-s
Paste one file at a time instead of in
parallel

84
more Command
• The more command is a command line utility for viewing the contents of a file
or files once screen at a time.
🞂 Syntax :
more [-options] [file]
🞂 Example :
Option Use
more -c Clear screen before displaying
more -
number
To Specify how many lines are printed in the screen
for a given file
more -s Doesn’t display extra blank lines

85
more Command Example

86
more -
number
To Specify how many lines are printed in the
screen for a given file

87
more -c Clear screen before displaying

88
cmp Command
• cmp command in Linux/UNIX is used to compare the two files byte by byte and
helps you to find out whether the two files are identical or not.
• If a difference is found, it reports the byte and line number where the first
difference is found.
• If no differences are found, by default, cmp returns no output.
🞂 Syntax :
• cmp [OPTION]... FILE1 [FILE2 [SKIP1 [SKIP2]]]

89
cmp Command Example
Option Use
cmp -b Print differing bytes
cmp -i Skip a particular number of initial bytes from both the files
cmp -s
Do not print anything; only return an exit status indicating
whether the files differ
cmp -n Compare at most LIMIT bytes
cmp -l Print byte position and byte value for all differing bytes

90
cmp Command Example
cmp -b Print differing bytes

91
cmp Command Example
cmp -i
Skip a particular number of initial bytes from both the
files

92
cmp Command Example
cmp -s
Do not print anything; only return an exit status
indicating whether the files differ

93
cmp Command Example
cmp -n Compare at most LIMIT bytes

94
cmp Command Example
cmp -l
Print byte position and byte value for all differing
bytes

95
comm Command
• Compare two sorted files line by line.
🞂 Syntax :
comm [OPTION]... FILE1 FILE2
🞂 Example :

96
comm Command Example
Option Use
comm -
1
Suppress column 1 (lines unique to FILE1)
comm -
2
Suppress column 2 (lines unique to FILE2)
comm -
3
Suppress column 3 (lines that appear in both files)

97
diff(difference) Command
• This command is used to display the differences in the files by comparing the
files line by line
• diff analyzes two files and prints the lines that are different. Essentially, it
outputs a set of instructions for how to change one file to make it identical to
the second file.
🞂 Syntax :
diff [options] File1 File2
🞂 Example :
Option Use
diff -b Ignores spacing differences
diff -i Ignores case

98
diff Command Example
Special symbols are:
• a : add
• c : change
• d : delete

99
chmod(change mode) Command
• chmod is used to change the permissions of files or directories.
🞂 Syntax :
chmod [reference][operator][mode] file...
🞂 Example :
Referenc
e
Clas
s
Description
u owner file's owner
g group users who are members of the file's group
o
other
s
users who are neither the file's owner nor
members of the file's group
a all All three of the above

100
chmod(change mode) Command
Operator Description
+ Adds the specified modes to the specified classes
-
Removes the specified modes from the specified
classes
=
The modes specified are to be made the exact modes
for the specified classes
Permissi
on
Description
r Permission to read the file
w Permission to write (or delete) the file
x
Permission to execute the file, or, in the case of a
directory, search it

101
chmod Command Example
u owner
g group
o others
a all
r (read) 4
w (write) 2
x (execute) 1
no
permissions
0
• Each write, read, and execute permissions have following number
value:

102
chmod Command Example

103
chown(change owner) Command
• The chown command changes ownership of files and directories in a Linux
filesystem.
🞂 Syntax :
chown [OPTIONS] USER[:GROUP] FILE(s)

104
chown Command Example

105
chgrp(change group) Command
• The chgrp command is used to change group ownership of a file/directory.
🞂 Syntax :
chgrp [OPTION]… GROUP FILE/DIR…

106
chgrp Command Example

107
chgrp Command Example

108
file Command
• The file command is used to determine a file's type.
🞂 Syntax :
file [OPTIONS] file1 file2 …
🞂 Example :

109
file Command Example
file -i
To view the mime type of a file rather than the human
readable format

110
finger Command
• finger looks up and displays information about system users.
🞂 Syntax :
finger [-option] [username]
🞂 Example :

111
finger Command Example
finger -
m
Match arguments only on user name (not first or last
name)

112
finger Command Example
finger -l Force long output format

113
sleep Command
• The sleep command is used to delay for a specified amount of time.
🞂 Syntax :
sleep NUMBER[SUFFIX]...
🞂 Example :

114
sleep Command Example
• s for seconds; this is a default one if you don’t specify any letter after the
integer.
• m for minutes.
• h for hours.
• d for days.

115
ps Command
• Reports a snapshot of the status of currently running processes.
🞂 Syntax :
ps [option]
🞂 Example :
Optio
n
Use
ps -e
Display every active process on a Linux system in
generic (Unix/Linux) format
ps -x View all processes owned by you
ps -f To provide more information on processes
ps -u Filter processes by its user

116
ps Command Example
ps -e
Display every active process on a Linux system in
generic (Unix/Linux) format

117
ps Command Example
ps -x View all processes owned by you

118
ps Command Example
ps -f To provide more information on processes

119
kill Command
• It is used to terminate processes manually.
• kill command sends a signal to a process which terminates the process.
• If the user doesn’t specify any signal which is to be sent along with kill
command then default TERM signal is sent that terminates the process..
🞂 Syntax :
kill [option] PID

120
kill Command Example

121
kill Command Example
Kill -l To display all the available signals

122
wc Command
• It s used to find out number of newline count, word count, byte and characters
count in a files specified by the file arguments.
🞂 Syntax :
wc [options] filenames
Optio
n
Use
wc -l Prints the number of lines in a file
wc -w Prints the number of words in a file
wc -c Displays the count of bytes in a file
wc -L Prints only the length of the longest line in a file

123
wc Command Example
wc -L Prints only the length of the longest line in a file

124
wc Command Example
wc -l Prints the number of lines in a file
wc -w Prints the number of words in a file
wc -c Displays the count of bytes in a file

125
ln Command
• ln creates links between files.
• ln creates hard links by default, or symbolic links if the -s (--symbolic) option is
specified. When creating hard links, each TARGET must exist.
🞂 Syntax :
ln [OPTION]… [-T] TARGET LINK_NAME
Optio
n
Use
ln -f If the destination file or files already exist, overwrite them
ln -i Prompt the user before overwriting destination files
ln -s Make symbolic links instead of hard links

126
ln Command Example

127
ln Command Example
f2.txt
(hello good morning)
f6.txt
(hello good
morning)
ln -s Make symbolic links instead of hard links

128
nl Command
• nl command numbers the lines in a file.
🞂 Syntax :
nl [OPTION]... [FILE]...
🞂 Example :
Optio
n
Use
nl -i Line number increment at each line
nl -s Add STRING after (possible) line number
nl -w Use NUMBER columns for line numbers

129
nl Command Example

130
nl Command Example
nl -i Line number increment at each line

131
nl Command Example
nl -s Add STRING after (possible) line number

132
nl Command Example
nl -w Use NUMBER columns for line numbers

133
head Command
• head makes it easy to output the first part (10 lines by default) of files.
🞂 Syntax :
head [OPTION]... [FILE]...
🞂 Example :
Optio
n
Use
head -
n
Print the first n lines instead of the first 10; with the
leading '-', print all but the last n lines of each file
head -c
Print the first n bytes of each file; with a leading '-', print
all but the last n bytes of each file
head -
q
Never print headers identifying file names

134
head Command Example

135
head -
n
Print the first n lines instead of the first 10; with the
leading '-', print all but the last n lines of each file

136
head -
c
Print the first n bytes of each file; with a leading '-',
print all but the last n bytes of each file

137
head -
q
Never print headers identifying file names

138
tail Command
• tail is a command which prints the last few number of lines (10 lines by default)
of a certain file, then terminates.
🞂 Syntax :
tail [OPTION]... [FILE]...
Optio
n
Use
tail -n Output the last num lines, instead of the default (10)
tail -c Output the last num bytes of each file
tail -q Never output headers

139
tail Command Example

140
tail -n Output the last num lines, instead of the default (10)

141
tail -c Output the last num bytes of each file

142
sort Command
• sort command is used to sort a file, arranging the records in a particular order.
• By default, the sort command sorts file assuming the contents are ASCII. Using
options in sort command, it can also be used to sort numerically.
🞂 Syntax : sort [OPTION]... [FILE]...
Option Use
sort -c To check if the file given is already sorted or not
sort -r Reverse the result of comparisons
sort -n Compare according to string numerical value
sort -nr To sort a file with numeric data in reverse order
sort -k Sorting a table on the basis of any column
sort -b Ignore leading blanks

143
sort Command Example

144
sort -c To check if the file given is already sorted or not

145
sort -r Reverse the result of comparisons

146
sort -n Compare according to string numerical value
sort -nr To sort a file with numeric data in reverse order

147
sort -k Sorting a table on the basis of any column

148
find Command
• find command searches for files in a directory hierarchy.
🞂 Syntax :
find [option] [path...] [expression]
Option Use
find -name
filename
Search for files that are specified by
‘filename’
find -newer
filename
Search for files that were modified/created
after ‘filename’
find -user name
Search for files owned by user name or ID
‘name’
find -size +N/-N
Search for files of ‘N’ blocks; ‘N’ followed by
‘c’ can be used to measure size in characters
find -empty Search for empty files and directories
find -perm octal Search for the file if permission is ‘octal’

149
find Command Example

150
find -newer
filename
Search for files that were
modified/created after ‘filename’

151
find -user name
Search for files owned by user name or ID
‘name’

152
find -size +N/-N
Search for files of ‘N’ blocks; ‘N’ followed
by ‘c’ can be used to measure size in
characters

153
find -
empty
Search for empty files and directories

154
uniq Command
• uniq reports or filters out repeated lines in a file.
• It can remove duplicates, show a count of occurrences, show only repeated
lines, ignore certain characters and compare on specific fields.
🞂 Syntax :
uniq [OPTION]... [INPUT [OUTPUT]]
Optio
n
Use
uniq -u Prints only unique lines
uniq -d Only print duplicated lines
uniq -D Print all duplicate lines
uniq -c
Prefix lines with a number representing how many times
they occurred
uniq -i Ignore case when comparing

155
uniq Command Example

156
uniq -u Prints only unique lines

157
uniq -d Only print duplicated lines

158
grep Command
• The grep filter searches a file for a particular pattern of characters, and displays
all lines that contain that pattern.
• The pattern that is searched in the file is referred to as the regular expression.
• grep stands for globally search for regular expression and print out.
🞂 Syntax :
grep [options] pattern [files]
Optio
n
Use
grep -c Prints only a count of the lines that match a pattern
grep -h
Display the matched lines, but do not display the
filenames
grep -l Displays list of a filenames only

159
grep Command Example

160
grep -c
Prints only a count of the lines that match a
pattern
grep -h
Display the matched lines, but do not display the
filenames
grep -l Displays list of a filenames only

161
grep -n Display the matched lines and their line numbers

162
grep -v
This prints out all the lines that do not matches
the pattern

163
grep -w Match whole word

164
grep -o Print only the matched parts of a matching line

165

166
pipe (|) Command
• It redirects the command STDOUT or standard output into the given next
command STDIN or standard input.
• In short, the output of each process directly as input to the next one like a
pipeline.
• The symbol '|' denotes a pipe.
• Pipes help you mash-up two or more commands at the same time and run them
consecutively.
🞂 Syntax :
command_1 | command_2 | command_3 | .... | command_N…

167
pipe Command Example

168

169

170
tr(translate) Command
• The tr command in UNIX is a command line utility for translating or deleting
characters.
• It supports a range of transformations including uppercase to lowercase,
squeezing repeating characters, deleting specific characters and basic find and
replace.
• It can be used with UNIX pipes to support more complex translation.
• tr stands for translate.
🞂 Syntax :
tr [OPTION] SET1 [SET2]

171
tr(translate) Command
🞂 POSIX Character set supported by tr command :
• [:digit:] Only the digits 0 to 9.
• [:alnum:] Any alphanumeric character.
• [:alpha:] Any alpha character A to Z or a to z.
• [:blank:] Space and TAB characters only.
• [:xdigit:] Hexadecimal notation 0-9, A-F, a-f.
• [:upper:] Any alpha character A to Z.
• [:lower:] Any alpha character a to z..
Option Use
tr -s
Replaces repeated characters listed in the set1 with single
occurrence
tr -d Delete characters in string1 from the input
tr -c
complements the set of characters in string. i.e., operations apply
to characters not in the given set
tr -cd Remove all characters except digits

172
tr Command Example

173
tr Command Example

174
tr Command Example
tr -s
Replaces repeated characters listed in the set1 with single
occurrence

175
tr Command Example
tr -d Delete characters in string1 from the input

176
tr Command Example
tr -c
complements the set of characters in string.
i.e., operations apply to characters not in the given set

177
tr Command Example
tr -cd Remove all characters except digits

178
history Command
• history command is used to view the previously executed command.
🞂 Syntax :
history
🞂 Example :

179
history Command Example

180
write Command
• write sends a message to another user.
🞂 Syntax :
write user [ttyname]
🞂 Example
Optio
n
Use
user The user to write to
tty
The specific terminal to write to, if the user is logged in to
more than one session

181
write Command Example
• Open first
terminal.
• Open Second terminal then execute command on
first terminal.

182
wall Command
• wall send a message to everybody’s terminal.
• wall sends a message to everybody logged in with their mesg permission set to
yes.
🞂 Syntax :
wall [-n] [-t TIMEOUT] [file]
🞂 Example
Optio
n
Use
wall -n --nobanner Suppress banner
wall -t
--timeout TIMEOUT Write timeout to terminals in
seconds. TIMEOUT must be positive integer. Default
value is 300 seconds, which is a legacy from time when
people ran terminals over modem lines.

183
wall Command Example
• Open four different terminal, execute command on first terminal, message
will display on everybody’s terminal.

184

185
Shell Script
🞂 Script is a sequence of commands written as plain text and run by an
interpreter (shell).
🞂 A shell script is a computer program designed to be run by the Unix/Linux shell
which could be one of the following:
⮩ The Bourne Shell
⮩ The C Shell
⮩ The Korn Shell
⮩ The GNU Bourne-Again Shell

186
Shell Script - Cont.…
🞂 The prompt, $, which is called the command prompt, is issued by the shell.
While the prompt is displayed, you can type a command.
🞂 The shell interprets commands the user types and manages their execution.
🞂 A shell is a command-line interpreter and typical operations performed by shell
scripts include file manipulation, program execution, and printing text.

187
Steps to write and execute a shell script
1. Create a file using a vi editor(or any other editor like gedit).
2. Name script file with extension .sh
3. Write some code.
4. Save the script file as filename.sh
5. For executing the script type bash filename.sh

188
Shell Variables
🞂 The user variable name can be any sequence of letters, digits, and the
underscore character, but the first character must be a letter.
🞂 To assign a value to a variable:
number=25
name=“abc"
🞂 There cannot be any space before or after the “=“
🞂 Internally, all values are stored as strings.
🞂 To use a variable, precede the name with a “$”.
num=3
a=$num

189
User input in Shell Script
🞂 The read command allows a user to provide the runtime input.
🞂 Shell allows to prompt for user input.
🞂 Syntax:
read varname [more vars]
• Value entered by user is assigned to varname
🞂 Run shell script :
bash filename.sh

190
Operators
Arithmetic Operators
Bash Operator Operator Description
+ + Addition
- - Subtraction
* * Multiplication
/ / Division
% % Modulus
Assignment Operators
= =
Assigns right operand
in left operand i.e. a=$b

191
Operators
Relational Operators – for Numeric
-eq == Equal
-ne != Not equal
-gt > Greater than
-ge >= Greater than or equal
-lt < Less than
-le <= Less than or equal
-z == null Is null

192
Operators
Relational Operators – for String
= or == == Equal
!= != Not equal
str1 < str2 < str1 is less than str2
str1 > str2 > str1 is greater str2

193
Operators
Boolean Operators
! ! This is logical negation.
-o OR This is logical OR.
-a AND This is logical AND.
String Operators
= =
Checks if the value of two
operands are equal or not
!= !=
If values are not equal then the
condition becomes true.

194
Arithmetic Operator Example (e.g. a=10, b=20)
Operator Description Example
+ (Addition) Adds values on either side of the operator èxpr $a + $b` will give 30
- (Subtraction) Subtracts right hand operand from left hand operand èxpr $a - $b` will give -10
* (Multiplication) Multiplies values on either side of the operator èxpr $a * $b` will give 200
/ (Division) Divides left hand operand by right hand operand èxpr $b / $a` will give 2
% (Modulus) Divides left hand operand by right hand operand and
returns remainder
èxpr $b % $a` will give 0
= (Assignment) Assigns right operand in left operand a = $b assign value of b into a
== (Equality) Compares two numbers, if both are same then
returns true.
[ $a == $b ] would return false.
!= (Not Equality) Compares two numbers, if both are different then
returns true.
[ $a != $b ] would return true.

195
Relational Operator Example (e.g. a=10, b=20)
-eq Checks if the value of two operands are equal or not; if yes, then the
[ $a -eq $b ] is
not true.
-ne Checks if the value of two operands are equal or not; if values are not
equal, then the condition becomes true.
[ $a -ne $b ] is
true.
-gt Checks if the value of left operand is greater than the value of right
operand; if yes, then the condition becomes true.
[ $a -gt $b ] is
not true.
-lt Checks if the value of left operand is less than the value of right operand; if
yes, then the condition becomes true.
[ $a -lt $b ] is
true.
-ge Checks if the value of left operand is greater than or equal to the value of
right operand; if yes, then the condition becomes true. [ $a -ge $b ] is
not true.
-le Checks if the value of left operand is less than or equal to the value of right
operand; if yes, then the condition becomes true. [ $a -le $b ] is
true.

196
Boolean Operator Example (e.g. a=10, b=20)
! This is logical negation. This inverts a true condition into
false and vice versa.
[ ! false ] is true.
-o This is logical OR. If one of the operands is true, then the
[ $a -lt 20 -o $b -gt 100 ] is
true.
-a This is logical AND. If both the operands are true, then
the condition becomes true otherwise false.
[ $a -lt 20 -a $b -gt 100 ] is
false.

197
String Operator Example (e.g. a=“abc”, b=“efg”)
= Checks if the value of two operands are equal or not; if yes, then the
[ $a = $b ]
is not true.
!= Checks if the value of two operands are equal or not; if values are not
equal then the condition becomes true.
[ $a != $b ] is
true.
-z Checks if the given string operand size is zero; if it is zero length, then it
returns true.
[ -z $a ]
is not true.
-n Checks if the given string operand size is non-zero; if it is nonzero length,
then it returns true.
[ -n $a ]
is not false.
str Checks if str is not the empty string; if it is empty, then it returns false. [ $a ]
is not false.

198
expr Command
• The expr command in Unix evaluates a given expression and displays its
corresponding output.
• It is used for:
• Basic operations like addition, subtraction, multiplication, division, and
modulus on integers.
• Evaluating regular expressions, string operations like substring, length of
strings etc.
• Syntax : expr EXPRESSION
$ expr 3 + 5
output:
8
$ expr 3 *
5
output:
15
num1=10
num2=20
sum=`expr $num1 +
$num2`
echo $sum
output: 30
Backtic
k
sum=`expr $num1 +
$num2`

199
if Statement
• If statements use the if, then, else, and fi keywords.
• The condition goes in square brackets.
🞂 Syntax :
if [ <some test> ]
then
<commands>
fi
if [ $no -gt 100 ]
then
echo "Greater than
100"
fi
The spaces
before and after
the square
brackets
[ ] are required.

200
if Statement
if [ $a -gt $b ]
then
echo “A is Greater than
B"
fi
if [ $a -ne $b ]
then
echo “A is not eqal to
B"
fi
if [ `expr $mid1_total + $mid2_total` -gt
50 ]
then
echo “Total Marks is Greater than 50"
fi

201
if…else Statement
if [control
command]
then
<statements-1>
else
<statements-2>
fi
if [ $a -eq $b ]
then
echo "a is equal to b"
else
echo "a is not equal to
b"
fi
• executes statements-1 if condition is
true
• executes statements-2 if condition is
false

202
Nested if-else-fi Statement
if [control command]
then
then
<statements>
else
<statements>
fi
else
<statements>
fi

203
if-else-if ladder
then
<statements>
elif [control command]
then
<statements>
elif [control command]
then
<statements>
else
<statements>
fi
• The word elif stands for “else if”
• It is part of the if statement and cannot be used by
itself

204
if-else-if ladder Example
if [ $i -eq 5 ]
then
echo "Value of i is 5"
elif [ $i -eq 10 ]
then
elif [ $i -eq 20 ]
then
elif [ $i -eq 30 ]
then
else
echo "Value of i is not equal to 5,10,20 or
30"
fi

205
case Structure
case $word in
pattern1) c
ommand-list1
;;
pattern2)
command-list2
;;
patternN)
command-listN
;;
*)
;;
esac
echo "Enter number:"
read num
case $num in
1)
echo "It's one!"
;;
2)
echo "It's two!"
;;
3)
echo "It's three!"
;;
*)
echo "It's something else!"
;;
esac
• Use the case statement for a decision that is based on
multiple choices.

206
Repetition Constructs
206

207
while loop
Syntax:
while [ condition
]
do
command1
command2
…..
.....
done
i=1
while [ $i -le 10 ]
do
echo “$i”
i=`expr $i + 1`
done
The while construct tests for a
condition, and if true, executes
commands.
It keeps looping as long as the
condition is true.

208
until loop
Syntax:
until [ condition ]
do
command1
command2
…..
.....
done
COUNT=1
until [ $COUNT -gt 5 ];
do
echo "Value of count is:
$COUNT"
COUNT=$(($COUNT + 1))
done
The until construct tests for a
condition, and if false, executes
commands.
It keeps looping as long as the
condition is false (opposite of while
construct)

209
for loop using “in” and list of values
for i in 1 2 3 4 5
do
echo "Looping ...
number $i"
done
for arg in list
do
command(s)
...
done
• Where the value of the variable arg is set to the values
provided in the list one at a time and the block of statements
executed.
• This is repeated until the list is exhausted.

210
for loop using C like Syntax
for((i=1; i<=5; i++))
do
echo $i
done
for ((initialization; condition test; increment or
decrement))
do
//statements to be executed repeatedly
done

211
select loop
select variableName in choice1 choice2 ...
choiceN
do
-- Block of Commands –
done
• Select command use PS3 variable to print its prompt.
• Each word in list is printed on screen preceded by a number.
• If the line consists of the number corresponding to one of the
displayed words (from the list), then varName is set to that
word. You can use if..else.fi or case..in..esac to make a decision.
• If the line is empty, WORDS and the prompt are redisplayed.
• If EOF (end of file) is read, the command completes.
• The loop continues until a break (CTRL+C) is encountered.

212
select loop Example
echo "Enter space shuttle to get more information : "
# set shuttle list
select shuttle in Columbia Endeavour Challenger Discovery
do
echo "$shuttle selected"
done
Output:
Enter the space shuttle to get more information :
1) Columbia
2) Endeavor
3) Challenger
4) Discovery
#? 1
Columbia selected
#?

213
Break and Continue Statement
• All statement inside the loop executed as long as some condition are true.
• If break placed inside the loop, when loop reach the break statement it will
terminated out from the loop.
• If continue placed inside the loop, when loop reach the continue statement it
will not execute next lines of the loop and it will go to the next iteration.

214
Break and Continue Statement
while [ condition ]
do
cmd-1
break
cmd-n
done
echo "done"
break statement continue statement
This iteration is over and
there are no more
iterations
This iteration is over, do
the next iteration
while [ condition ]
do
cmd-1
continue
cmd-n
done
echo "done"

215
echo and printf Command
echo Command printf Command
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1234
5
1234
5
Decimal:
100
Octal: 144
Hex: 64

216
Average of 4 numbers using bc Command
a=10
b=2
c=12
d=5
sum=$(( a + b + c + d))
avg=`echo $sum / 4 | bc –l`
printf %0.3f “$avg”
OUTPUT :
7.250

217
Division using bc Command
# get the first number
printf "Enter first integer number: "
read a
# get the second number
printf "Enter second integer number: "
read b
# if b is 0
if [ $b == 0 ]
then
printf "Division by 0 not allowed.n"
exit # exit the script
fi
# perform division
result=`expr "$a / $b" | bc -l`
printf "%d / %d = %.5fn" "$a" "$b"
"$result"

218

Darshan Institute of Engineering &
Technology, Rajkot
Than
k
You
Operating System (OS)
GTU # 3140702
maulik.trivedi@darshan.ac.in
9998 265 805
Computer Engineering Department

Unix Commands and Shells Scripts in OS.pptx

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