How do you write an IF ELSE statement in Linux?

The if statement starts with the if keyword followed by the conditional expression and the then keyword. The statement ends with the fi keyword. If the TEST-COMMAND evaluates to True , the STATEMENTS gets executed. If TEST-COMMAND returns False , nothing happens; the STATEMENTS get ignored.

How do you write else if in Linux?

The “if’ keyword is followed by the condition you want to check. In this if-else-if conditional statement, the expressions are evaluated from top to bottom. This is followed by “then” keyword. After that, if an expression is evaluated to true, corresponding statements are executed.

How do you write if-else in shell script?

Their description with syntax is as follows:

  1. if statement. This block will process if specified condition is true. …
  2. if-else statement. …
  3. if..elif..else..fi statement (Else If ladder) …
  4. if..then..else..if..then..fi..fi..(Nested if) …
  5. Syntax: case in Pattern 1) Statement 1;; Pattern n) Statement n;; esac. …
  6. Example 2:

How do you do an if-else statement?

Use if to specify a block of code to be executed, if a specified condition is true. Use else to specify a block of code to be executed, if the same condition is false. Use else if to specify a new condition to test, if the first condition is false.

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What is the if statement?

An if statement is a programming conditional statement that, if proved true, performs a function or displays information. … In the example above, if the value of X were equal to any number less than 10, the program displays, “Hello John” when the script is run.

What is in if statement in Linux?

if is a command in Linux which is used to execute commands based on conditions. The ‘if COMMANDS’ list is executed. … Otherwise, the ‘else COMMANDS’ list is executed, if present. The exit status of the entire construct is the exit status of the last command executed, or zero if no condition tested true.

What is $1 in Bash script?

$1 is the first command-line argument passed to the shell script. Also, know as Positional parameters. … $0 is the name of the script itself (script.sh) $1 is the first argument (filename1) $2 is the second argument (dir1)

How do I run a shell script?

Steps to write and execute a script

  1. Open the terminal. Go to the directory where you want to create your script.
  2. Create a file with . sh extension.
  3. Write the script in the file using an editor.
  4. Make the script executable with command chmod +x <fileName>.
  5. Run the script using ./<fileName>.

How do you read a file in shell?

How to Read a File Line By Line in Bash. The input file ( $input ) is the name of the file you need use by the read command. The read command reads the file line by line, assigning each line to the $line bash shell variable. Once all lines are read from the file the bash while loop will stop.

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What is if in bash script?

In bash scripting, as in the real world, ‘if’ is used to ask a question. The ‘if’ command will return a yes or no style answer and you can script the appropriate response.

What is bash if statement?

In Bash, the if statement is part of the conditional constructs of the programming language. The if in a Bash script is a shell keyword that is used to test conditions based on the exit status of a test command. An exit status of zero, and only zero, is a success, i.e. a condition that is true.

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