How do I run 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.
How use if in Linux?
if is a command in Linux which is used to execute commands based on conditions. The ‘if COMMANDS’ list is executed. If its status is zero, then the ‘then COMMANDS’ list is executed.
How do I write an if in a .sh file?
Their description with syntax is as follows:
- if statement. This block will process if specified condition is true. …
- if-else statement. …
- if..elif..else..fi statement (Else If ladder) …
- if..then..else..if..then..fi..fi..(Nested if) …
- Syntax: case in Pattern 1) Statement 1;; Pattern n) Statement n;; esac. …
- Example 2:
How do I write an if statement in bash?
The syntax of an bash if statement
A short explanation of the example: first we check if the file somefile is readable (“if [ -r somefile ]”). If so, we read it into a variable. If not, we check if it actually exists (“elif [ -f somefile ]”).
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 $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)
What is in if condition in Linux?
Syntax. This code is just a series of if statements, where each if is part of the else clause of the previous statement. Here statement(s) are executed based on the true condition, if none of the condition is true then else block is executed.
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.
How do I run a shell script?
Steps to write and execute a script
- Open the terminal. Go to the directory where you want to create your script.
- Create a file with . sh extension.
- Write the script in the file using an editor.
- Make the script executable with command chmod +x <fileName>.
- Run the script using ./<fileName>.
What is =~?
The =~ operator is a regular expression match operator. This operator is inspired by Perl’s use of the same operator for regular expression matching.
What is if Z in shell script?
The -z flag causes test to check whether a string is empty. Returns true if the string is empty, false if it contains something. NOTE: The -z flag doesn’t directly have anything to do with the “if” statement. The if statement is used to check the value returned by test.
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.
How do I get input in Bash?
To read the Bash user input, we use the built-in Bash command called read.
…
Program:
- #!/bin/bash.
- # Read the user input.
- echo “Enter the user name: “
- read first_name.
- echo “The Current User Name is $first_name”
- echo.
- echo “Enter other users’names: “
- read name1 name2 name3.
How do I compare two numbers in Bash?
Example: Comparing numbers in bash
Find out if 5 greater than 10, enter (type command at terminal): x=5 y=10 [ $x -gt $y ] echo $?
How do you call a function in Bash?
To invoke a bash function, simply use the function name. Commands between the curly braces are executed whenever the function is called in the shell script. The function definition must be placed before any calls to the function.