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fc Command in Linux with Examples

expr command in Linux with examples

Last Updated : 30 Aug, 2024

The expr command in Unix is a versatile tool used for evaluating expressions in the shell environment. It performs a wide range of functions, including arithmetic calculations, string operations, and comparisons based on regular expressions.

What is the ‘expr’ Command?

expr stands for “expression” and allows for the evaluation of values and returns the result to standard output. It is particularly useful in scripts for handling both numerical and string data efficiently. In short, it helps in:

Basic operations like addition, subtraction, multiplication, division, and modulus on integers.
Evaluating regular expressions, string operations like substring, length of strings etc.

Syntax:

$expr expression

Key Options:

‘–version’: It is used to show the version information. Syntax:
```
$expr --version 
```
Example:
‘–help’: It is used to show the help message and exit. Syntax:
```
$expr --help 
```
Example:

‘expr’ Command Examples

Below are some examples to demonstrate the use of “expr” command:

1. Using expr for basic arithmetic operations :

Example 1: Addition

$expr 12 + 8

Example 2: Multiplication

$expr 12 \* 2

Output

Note: The multiplication operator * must be escaped when used in an arithmetic expression with ‘expr’.

2. Performing operations on variables inside a shell script

Example: Adding two numbers in a script

echo "Enter two numbers" read x  read y sum=`expr $x + $y` echo "Sum = $sum"

Output:

Note: ‘expr’ is an external program used by Bourne shell. It uses ‘expr’ external program with the help of backtick. The backtick(`) is actually called command substitution.

3. Comparing two expressions

Example 1: Equality Check

x=10 y=20  # matching numbers with '=' res=`expr $x = $y` echo $res  # displays 1 when arg1 is less than arg2 res=`expr $x \< $y` echo $res  # display 1 when arg1 is not equal to arg2 res=`expr $x \!= $y` echo $res

Output:

Example 2: Evaluating boolean expressions

# OR operation $expr length  "geekss"  "<"  5  "|"  19  -  6  ">"  10

Output:

# AND operation $expr length  "geekss"  "<"  5  "&"  19  -  6  ">"  10

Output:

4. For String operations

Example 1: Finding length of a string

x=geeks len=`expr length $x` echo $len

Output:

Example 2: Finding substring of a string

x=geeks  sub=`expr substr $x 2 3`  #extract 3 characters starting from index 2  echo $sub

Output:

Example 3: Matching number of characters in two strings

$ expr geeks : geek

Output:

Conclusion

The ‘expr’ command is an indispensable tool for scripting in Unix-like systems, offering a broad array of functionalities from mathematical calculations to complex string manipulations. By mastering ‘expr’, users can enhance their scripts’ capabilities and perform sophisticated data processing tasks efficiently.

fc Command in Linux with Examples

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