bash compare variables

1. How do I compare two variables in bash?
2. What is == in bash?
3. How do you check if a variable is equal to a string in Shell?
4. What is the difference between the $@ and $* variables?
5. How do I increment a variable in bash?
6. How do you set a variable in bash?
7. What is $1 in bash script?
8. What is option in bash?
9. Which variable contains shell process?
10. How do you check a variable in bash?
11. Is variable empty bash?
12. Is equal in bash?

How do I compare two variables in bash?

Comparison Operators

When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. Use the = operator with the test [ command. Use the == operator with the [[ command for pattern matching.

What is == in bash?

It's the other way around: = and == are for string comparisons, -eq is for numeric ones. -eq is in the same family as -lt , -le , -gt , -ge , and -ne , if that helps you remember which is which. == is a bash-ism, by the way. ... In bash the two are equivalent, and in plain sh = is the only one guaranteed to work.

How do you check if a variable is equal to a string in Shell?

Details

1. Use == operator with bash if statement to check if two strings are equal.
2. You can also use != to check if two string are not equal.
3. You must use single space before and after the == and != operators.

What is the difference between the $@ and $* variables?

The $@ holds list of all arguments passed to the script. The $* holds list of all arguments passed to the script. ... They appear to work the same in my scripts.

How do I increment a variable in bash?

Using + and - Operators

The most simple way to increment/decrement a variable is by using the + and - operators. This method allows you increment/decrement the variable by any value you want.

How do you set a variable in bash?

To create a variable, you just provide a name and value for it. Your variable names should be descriptive and remind you of the value they hold. A variable name cannot start with a number, nor can it contain spaces. It can, however, start with an underscore.

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 option in bash?

Options are settings that change shell and/or script behavior. The set command enables options within a script. At the point in the script where you want the options to take effect, use set -o option-name or, in short form, set -option-abbrev. ... #!/bin/bash set -o verbose # Echoes all commands before executing.

Which variable contains shell process?

There is a special variable called "$" and "$BASHPID" which stores the process ID of the current shell. Go ahead and run the below command to see what is the process ID of your current shell. Both "$" and "$BASHPID" is going to return the same value.

How do you check a variable in bash?

To check if a variable is set in Bash Scripting, use -v var or -z $var as an expression with if command. This checking of whether a variable is already set or not, is helpful when you have multiple script files, and the functionality of a script file depends on the variables set in the previously run scripts, etc.

Is variable empty bash?

To find out if a bash variable is empty:

Return true if a bash variable is unset or set to the empty string: if [ -z "$var" ]; Another option: [ -z "$var" ] && echo "Empty" Determine if a bash variable is empty: [[ ! -z "$var" ]] && echo "Not empty" || echo "Empty"

Is equal in bash?

You can check the equality and inequality of two strings in bash by using if statement. “==” is used to check equality and “!= ” is used to check inequality of the strings. You can partially compare the values of two strings also in bash.