How do you write an IF condition in shell?

How do you write an IF condition in shell?

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:

What does =~ mean in bash?

It’s a regular expression match operator. From the bash man page: An additional binary operator, =~, is available, with the same precedence as == and != . When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex(3)).

What does $_ mean in shell?

$_ :- Is a Special variable set to last argument of previous command executed. Examples:- #!/bin/bash echo $_ # /bin/bash # Just called /bin/bash to run the script.

How do I write an if 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.

What is $# in shell script?

$# : This variable contains the number of arguments supplied to the script. $? : The exit status of the last command executed. Most commands return 0 if they were successful and 1 if they were unsuccessful. Comments in shell scripting start with # symbol.

How do you end an if statement in shell script?

2 Answers. Try replacing the last line ( endif ) with fi , which is the correct token to close an if statement. Also, replace ($2 == “both”) with the correct [ $2 == “both” ] . Note the quotes around $2 , the spaces after [ and before ] and the ; before the then .

What does << do in Linux?

A command with the << operator will do the following things :

1. Launch the program specified in the left of the operator, cat for instance.
2. Grab user input, including newlines, until what is specified on the right of the operator is met on one line, EOF for instance.

What does 1 & 2 mean in shell script?

0. 8. File descriptor 1 is stdout and File descriptor 2 is stderr . Using > to redirect output is the same as using 1> .

What does $_ mean in Linux?

$_ means the last argument to the previous command. Example: echo “FOO” “BAR” FOO BAR echo $_ BAR. Read more here. https://unix.stackexchange.com/questions/320046/what-is-mean/320052#320052. Copy link CC BY-SA 3.0.

What is the shell in Linux?

The shell is the Linux command line interpreter. It provides an interface between the user and the kernel and executes programs called commands. For example, if a user enters ls then the shell executes the ls command.

What does $# mean in Linux?

number of arguments
$# is the number of arguments, but remember it will be different in a function. $# is the number of positional parameters passed to the script, shell, or shell function. This is because, while a shell function is running, the positional parameters are temporarily replaced with the arguments to the function.

What is exit code in Linux?

What is an exit code in the UNIX or Linux shell? An exit code, or sometimes known as a return code, is the code returned to a parent process by an executable. On POSIX systems the standard exit code is 0 for success and any number from 1 to 255 for anything else.

How does the if statement in shell work?

If the first condition is false, then subsequent elif statements are checked. When an elif condition is found to be true, the statements following the associated then statement are executed. Algorithm for if condition in unix shell script. The if statement uses the exit status of the given condition.

What does if.else.fi mean in Linux?

If..else..fi. if..else..fi allows to make choice based on the success or failure of a command. For example, find out if file exists (true condition) or not (false condition) and take action based on a condition result.

What happens if if else is true in shell script?

If the “if-else “condition is “true” then the first group of statements will execute. If the condition is “false” then the second group of statements will execute. As per the above flow, the interpreter will execute the “if condition”.

How to validate if then Fi Fi in shell scripting?

Working of if_then_else_if_then_fi_fi (Nested if) in Shell Scripting: In nested if condition, we can validate the multiple “if-else” conditions. The interpreter will validate the first condition of the “if_else”. If the condition is true then the further “if_else” condition will validate.