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man pages section 1: User Commands

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Updated: Wednesday, February 9, 2022



expr - evaluate arguments as an expression


/usr/bin/expr argument...
/usr/xpg4/bin/expr argument...
/usr/xpg6/bin/expr argument...


/usr/bin/expr, /usr/xpg4/bin/expr

The expr utility evaluates the expression and writes the result to standard output. The character 0 is written to indicate a zero value and nothing is written to indicate a null string.


The expr utility evaluates the expression and writes the result to standard output followed by a NEWLINE. If there is no result from expr processing, a NEWLINE is written to standard output.


The argument operand is evaluated as an expression. Terms of the expression must be separated by blanks. Characters special to the shell must be escaped (see sh(1)). Strings containing blanks or other special characters should be quoted. The length of the expression is limited to LINE_MAX (2048 characters).

The operators and keywords are listed below. The list is in order of increasing precedence, with equal precedence operators grouped within { } symbols. All of the operators are left-associative.

expr | expr

Returns the evaluation of the first expr if it is neither NULL nor 0; otherwise, returns the evaluation of the second expr if it is not NULL; otherwise, 0.

expr & expr

Returns the first expr if neither expr is NULL or 0, otherwise returns 0.

expr { =, >, >=, <, <=, != } expr

Returns the result of an integer comparison if both arguments are integers, otherwise returns the result of a string comparison using the locale-specific coalition sequence. The result of each comparison is 1 if the specified relationship is TRUE, 0 if the relationship is FALSE.

expr { +, } expr

Addition or subtraction of integer-valued arguments.

expr { *, /, % } expr

Multiplication, division, or remainder of the integer-valued arguments.

expr : expr

The matching operator : (colon) compares the first argument with the second argument, which must be an internationalized basic regular expression (BRE), except that all patterns are anchored to the beginning of the string. That is, only sequences starting at the first character of a string are matched by the regular expression. See regex(7) and NOTES. Normally, the /usr/bin/expr matching operator returns the number of bytes matched and the /usr/xpg4/bin/expr matching operator returns the number of characters matched (0 on failure). If the second argument contains at least one BRE sub-expression [\(...\)], the matching operator returns the string corresponding to \1.


An argument consisting only of an (optional) unary minus followed by digits.


A string argument that cannot be identified as an integer argument or as one of the expression operator symbols.

The following four operators: index, length, match, and substr, are all at the same precedence:

index string character-list

Report the first byte in string (counting from one) where a byte from character-list matches a byte from string. If no bytes in character-list appear in string, a 0 is returned.

length string

Return the length (that is, the number of bytes) of string. The terminating nul character is not included in that count.

match string regular-expression

Synonymous with the expr : expr matching operator.

substr string integer-1 integer-2

Extract the sequence of bytes from string (counting from one) starting at position integer-1 and of length integer-2 bytes. If integer-1 has a value greater than the number of bytes in string, expr returns a null string. If you try to extract more bytes than there are in string, expr returns all the remaining bytes from string. Results are unspecified if either integer-1 or integer-2 is a negative value.


Example 1 Adding an integer to a shell variable

Add 1 to the shell variable a:

example$ a=`expr  $a  +  1`
Example 2 Returning a path name segment

The following example emulates basename(1), returning the last segment of the path name $a. For $a equal to either /usr/abc/file or just file, the example returns file. (Watch out for / alone as an argument: expr takes it as the division operator. See NOTES below.)

example$ expr $a : '.*/\(.*\)' \| $a
Example 3 Using // characters to simplify the expression

Here is a better version of the previous example. The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression.

example$ expr //$a : '.*/\(.*\)'


Example 4 Returning the number of bytes in a variable
example$ expr "$VAR" : '.*'


Example 5 Returning the number of characters in a variable
example$ expr "$VAR" : '.*'

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of expr: LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, and NLSPATH.

Exit Status

As a side effect of expression evaluation, expr returns the following exit values:


If the expression is neither NULL nor 0.


If the expression is either NULL or 0.


For invalid expressions.

> 2

An error occurred.


See attributes(7) for descriptions of the following attributes:

Enabled. See Notes.
Interface Stability
See below.

The match, substr, length, and index operators are Uncommitted. Everything else is Committed.

See Also

basename(1), echo(1), ed(1), sh(1), Intro(3), attributes(7), environ(7), regex(7), standards(7)


syntax error

Operator and operand errors.

non-numeric argument

Arithmetic is attempted on such a string.


Operators Not CSI-Enabled

The following three operators are not CSI enabled. They are also not available in /usr/xpg4/bin/expr and /usr/xpg6/bin/expr:

index string character-list

length string

substr string integer-1 integer-2

After argument processing by the shell, expr cannot tell the difference between an operator and an operand except by the value. If $a is an =, the command:

example$ expr $a = '='

looks like:

example$ expr = = =

as the arguments are passed to expr (and they are all taken as the = operator). The following works:

example$ expr X$a = X=

Regular Expressions

Unlike some previous versions, expr uses Internationalized Basic Regular Expressions for all system-provided locales. Internationalized Regular Expressions are explained on the regex(7) manual page.

Operator Precedence Order in Other Versions

In previous releases of Solaris, there was a /usr/ucb/expr command that had a different operator precedence order than the expr command described here. Also, the /usr/gnu/bin/expr command has its own unique operator precedence order.