expr command in Linux with examples

The expr command in Unix evaluates a given expression and displays its corresponding output. It is used for:

• 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

Options:

• Option –version : It is used to show the version information.

  Syntax:

  $expr --version
  

  Example:

  

• Option –help : It is used to show the help message and exit.

  Syntax:

  $expr --help
  

  Example:

  

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

1. Using expr for basic arithmetic operations :

Example: Addition

$expr 12 + 8 

Example: 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:

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: 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: Finding length of a string

x=geeks

len=`expr length $x`

echo $len

Output:

Example: Finding substring of a string

x=geeks

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

echo $sub

Output:

Example: Matching number of characters in two strings

$ expr geeks : geek

Output: