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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.

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.

$expr expression

Key Options:

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

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'.

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.

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:

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:

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.

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