Shell Script

A shell provides us with an interface to the Unix system. It gathers input and executes based on the input and provides output. Shell is an environment in which we can run our commands, programs, and shell scripts

Shells could be one of the following :

• The Bourne Shell
• The C Shell
• The Korn Shell
• The GNU Bourne-Again Shell

A shell script is a computer program designed to be run by the Unix/Linux shell.

A Bash script is a plain text file which contains a series of commands

Creating Script File and Steps to run

• Create empty file and save the file with .sh extension to make the file as script file.
• To check the file is executable. run ls -l command.
• drwr-r--rw the file has only read and write access.
• drwxr-xr-x the file has read, write and execution access.
• To make file to execute: run chmod -x <file name> command
• To run script add #!/path to shelle.g: #!/bin/sh as first line in the script file
• #! is called shebang and echo : is for printing the line
• variables are declared as <variable name>=<value>

Variable declaration and printing variable value

IF Condition, while, for loop and switch case: (we can use single or double brace for condition)

Function in shell scripts

There are 4 type of functions.

1. function with parameter
2. function without parameter
3. function with return type
4. function without return type

Calling a function from different files

Exit Statements in shell script

1. If function executes successfully it returns 0 : exit status is 0
2. If function executes fails it returns nonZero : exit status might be 1 or any non zero value

Break and Continue Condition

• break: which breaks the execution of loop
• syntax: break or break nth
• break nth : it breaks nth closing loop
• In nested loop break will stops execution of inner loop

break nth: example — break 2 : it breaks nested loops upto level 2

• Continue: If condition is success, which breaks the execution of loop and continues the next execution
• syntax: continue or continue nth
• continue nth : it breaks nth closing loop and continues next execution

continue nth: example — continue 2 : it breaks nested loops upto level 2 and continues the execution

Note:

• To get more detail please check my GitHub account for more details on syntax and live examples.
• To know more about shell command like grep, awk, cut, sed and pipe, please check the blog here

LAST REMARKS

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