How do you write an IF condition in Unix shell script?

How do you write an if statement 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:

What is in if condition in shell script?

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.

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.

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.

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How do you compare two variables in Unix?

Compare Numbers in Linux Shell Script

  1. num1 -eq num2 check if 1st number is equal to 2nd number.
  2. num1 -ge num2 checks if 1st number is greater than or equal to 2nd number.
  3. num1 -gt num2 checks if 1st number is greater than 2nd number.
  4. num1 -le num2 checks if 1st number is less than or equal to 2nd number.

What is in 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. … The exit status of the entire construct is the exit status of the last command executed, or zero if no condition tested true.

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>.

What is S in shell script?

The syntax of the s command is ‘ s/ regexp / replacement / flags ‘. Its basic concept is simple: the s command attempts to match the pattern space against the supplied regular expression regexp ; if the match is successful, then that portion of the pattern space which was matched is replaced with replacement .

What is E in shell script?

The -e option means “if any pipeline ever ends with a non-zero (‘error’) exit status, terminate the script immediately”. Since grep returns an exit status of 1 when it doesn’t find any match, it can cause -e to terminate the script even when there wasn’t a real “error”.

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What is $# in shell script?

$# is a special variable in bash , that expands to the number of arguments (positional parameters) i.e. $1, $2 … passed to the script in question or the shell in case of argument directly passed to the shell e.g. in bash -c ‘…’ …. .

How do I create a Bash file?

How to create a file in Linux from terminal window?

  1. Create an empty text file named foo.txt: touch foo.bar. …
  2. Make a text file on Linux: cat > filename.txt.
  3. Add data and press CTRL + D to save the filename.txt when using cat on Linux.
  4. Run shell command: echo ‘This is a test’ > data.txt.
  5. Append text to existing file in Linux:

How do you set a variable in Bash?

The easiest way to set environment variables in Bash is to use the “export” keyword followed by the variable name, an equal sign and the value to be assigned to the environment variable.

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