Fundamental of Shell Programming
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This document provides an overview of the fundamentals of Linux shell programming. It begins with an introduction and roadmap. It then covers topics like creating shell programs, variables, pipes, command line parameters, control structures like if/else and loops, functions, and arrays. Specific examples are given to demonstrate how to use variables, pipes, math expressions, test conditions, loops, functions, and pass parameters and return values. The document is intended to teach the basic concepts of shell programming and scripting.
![Basic of Shell Programming
●
Evaluating expression
–
Two ways to evaluate
●
●
●
Using expr expression
Using $[ expression]
They work differently for multiplication ( * )
|
#!/bin/bash
|
b=5
c=6
|
c=6
a=`expr $b + $c`
|
a=$[$b +$c]
echo “Sum =$a”
18/12/13
#!/bin/bash
b=5
–
|
echo “Sum=$a”
OpenLab
7](https://image.slidesharecdn.com/flsp-131218225247-phpapp01/85/Fundamental-of-Shell-Programming-7-320.jpg)
![Control Structure
●
If-then-else
testing of if condition using test & [ ]
Structure
Example
if command
| #!/bin/bash
then
| if test $1 -gt $2
command
fi
| then
| echo “First CL is greater”
| else
| echo “Second CL is greater”
18/12/13
OpenLab
12](https://image.slidesharecdn.com/flsp-131218225247-phpapp01/85/Fundamental-of-Shell-Programming-12-320.jpg)
![Creation of Function
●
Passing array in function
●
Decleration of array
Ex:- myarray = (1 2 3 4 5)
access values of array -- ${myarray[$1]} index 1
${myarray[*]} all array
–
18/12/13
Example FunArrVar.sh
OpenLab
23](https://image.slidesharecdn.com/flsp-131218225247-phpapp01/85/Fundamental-of-Shell-Programming-23-320.jpg)
Fundamental of Shell Programming
- 1. Fundamental of Linux & Shell Programming Presented By:-Rahul Hada hada.rahul@gmail.com Mob:- 9001806370
- 2. RoadMap ● Basic of shell programming – – Using variables – Pipes – Performing math – ● Creation of shell program Handling user input Control Structure – – if-then-else Loops ● ● For , while , until Creating Function 18/12/13 OpenLab 2
- 3. Basic of Shell Programming ● Creating a shell program – Specify the shell you are using in the first line – #!/bin/bash , #!/bin/ksh etc. – Ex: Shell program to print something #!/bin/bash echo “Welcome to the world of Shell Programming” ● Execution of program – Shell script never compile – First change mode then execute – cs@poornima$ chmod 775 hello.sh or chmod u+x – cs@poornima$ ./hello.sh 18/12/13 OpenLab 3
- 4. Basic of Shell Programming ● Variables – we can access the value of variable using $ sign. – Types of variables ● ● ● 18/12/13 Environment Variables – stores specific system information. ex. $HOME,$SHELL,$LANGUAGE, $HOSTNAME,$HOSTTYPE etc User Variables – stores our own values in a variable. Ex: #!/bin/bash | #!/bin/bash a=5 | read a echo “Value of a=$a” | echo “Value of a=$a” OpenLab 4
- 5. Basic of Shell Programming ● Backtick (` `) – It allow you to assign the output of a shell command to a variable – Ex:#!/bin/bash 18/12/13 | #!/bin/bash | d=`date` | echo date | echo $d date | #!/bin/bash | OpenLab 5
- 6. Basic of Shell Programming ● Pipes (|) – The output of one command is the input of the other command. – Command1 | command2 – grep poornima history.txt | wc -l – Ex: #!/bin/bash a=`grep poornima history | wc -l` echo “Number of Lines Containing Pattern=$a” 18/12/13 OpenLab 6
- 7. Basic of Shell Programming ● Evaluating expression – Two ways to evaluate ● ● ● Using expr expression Using $[ expression] They work differently for multiplication ( * ) | #!/bin/bash | b=5 c=6 | c=6 a=`expr $b + $c` | a=$[$b +$c] echo “Sum =$a” 18/12/13 #!/bin/bash b=5 – | echo “Sum=$a” OpenLab 7
- 8. Basic of Shell Programming ● Exiting the script Every command runs in the shell uses an exit status. ● Whose value vary from 0-255 ● Value stores on ? Or $? ● Explicit exit status from script ● cs@poornima$ echo $? #!/bin/bash #!/bin/bash | #!/bin/bash hello | ls -ytr | ls -l echo $? 18/12/13 | | echo $? | echo $? OpenLab 8
- 9. Basic of Shell Programming ● Exit Status Codes – 0 -------- successful completion of the command – 2 -------- misuse of shell commands – 127 -------- command not found – 130 -------- command terminated with Clt-C example using program 18/12/13 OpenLab 9
- 10. Basic of Shell Programming ● Command line Parameters – It allow you to add data values to the command line when you execute the script. – Ex : cs@poornima$./sum.sh 23 56 – Shell uses special variable, called positional parameters. – Represented from 0 – 9 i.e $0 - $9 #!/bin/bash s=`expr $1 + $2` echo “Sum=$s” 18/12/13 OpenLab 10
- 11. Basic of Shell Programming ● Some special variables releated to the command line parameters – $* , $@ , $# #!/bin/bash #!/bin/bash | #!/bin/bash echo $# – | | echo $* | echo $@ Shift command – it downgrades each parameter variable one position by default. #!/bin/bash ./cli1.sh 3 4 5 shift shift 18/12/13 echo $1 OpenLab 11
- 12. Control Structure ● If-then-else testing of if condition using test & [ ] Structure Example if command | #!/bin/bash then | if test $1 -gt $2 command fi | then | echo “First CL is greater” | else | echo “Second CL is greater” 18/12/13 OpenLab 12
- 13. Control Structure ● Test of numeric comparisons – n1 -gt n2 – n1 -eq n2 -- check if n1 is equal to n2 – n1 -lt n2 -- check if n1 is lesser then n2 – n1 -le n2 -- check if n1 is lesser or equal to n2 – n1 -ge n2 -- check if n1 is greater or equal to n2 – n1 -ne n2 -- check if n1 is not equal to n2 18/12/13 -- check if n1 is greater then n2 OpenLab 13
- 14. Control Structure ● Test of string comparisons – str1 = srt2 -- check if str1 is the same as str2 – str1 != str2 – check if str1 is not equal to str2 – str1 > str2 – check if str1 is greater then str2 – str1 < str2 – check is str1 is lesser then str2 – -n str1--check if str1 has a length greater then zero – -z str1-- check if str1 has length is zero Note : Must use escape () symbol while using > or < 18/12/13 OpenLab 14
- 15. Control Structure ● Test file comparisons – -d file -- check if file exist and is a directory – -e file -- check if file exist – -f file -- check if file exist and is a file – -r file -- check if file exist and is readable – -w file – check if file exist and is writable – -x file – check if file exist and is executable – and, few more 18/12/13 OpenLab 15
- 16. Control Structure ● Case Statement case variable in | | pattern3) command ;; case $ch in | command;; read ch | pattern1 | pattern2) #!/bin/bash a|e|i|o|u) | | *) command;; echo “char. is vowel” ;; | esac *) echo ”char is not vowel” | 18/12/13 | ;; | esac OpenLab 16
- 17. Control Structure ● Loops types in shell for , while , until for var in list do command done ● Different ways to represent for loop ● Can redirect the output of for loop in file ● For loop can take input from file 18/12/13 OpenLab 17
- 18. Control Structure ● While Loop while test condition do commands done 18/12/13 OpenLab 18
- 19. Control Structure ● Untile loop – works opposite way of while loop until test commands do commands done 18/12/13 OpenLab 19
- 20. Guess output ? #!/bin/bash | #!/bin/bash for var in” $*” | for var in “$@” do | do echo “Output=$var” | echo “Output=$var” done 18/12/13 |done OpenLab 20
- 21. Creation of function ● Function – reuse of same shell code ● In shell function is a mini-script ● Creation of function by two ways function name { commands } | name () { | commands | } | 18/12/13 OpenLab 21
- 22. Creation of Function ● ● Passing parameters in function Returing values from function can be three types :– By Default it return exit status of the last executed command in the function – We can also use return to modify the exit status as per our own requirement – Using echo to return values 18/12/13 OpenLab 22
- 23. Creation of Function ● Passing array in function ● Decleration of array Ex:- myarray = (1 2 3 4 5) access values of array -- ${myarray[$1]} index 1 ${myarray[*]} all array – 18/12/13 Example FunArrVar.sh OpenLab 23