EXPR(1) User Commands EXPR(1)


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
will be 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

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


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

Compatibility Operators (x86 only)
The following operators are included for compatibility with INTERACTIVE
UNIX System only and are not intended to be used by non- INTERACTIVE UNIX
System scripts:

index string character-list

Report the first position in which any one of the bytes in character-
list matches a byte in string.

length string

Return the length (that is, the number of bytes) of string.

substr string integer-1 integer-2

Extract the substring of string 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" : '.*'


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


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.

An error occurred.


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

|CSI | enabled |
|Interface Stability | Standard |


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


syntax error
Operator and operand errors.

non-numeric argument
Arithmetic is attempted on such a string.


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.

August 29, 2003 EXPR(1)