expr(1)
NAME
expr - evaluate arguments as an expression
SYNOPSIS
/usr/bin/expr argument...
/usr/xpg4/bin/expr argument...
DESCRIPTION
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.
OPERANDS
The argument operand is evaluated as an expression. Terms of
the expression must be separated by blanks. Characters spe-
cial to the shell must be escaped (see sh(1)). Strings con-
taining 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 opera-
tors grouped within {} symbols. All of the operators are
left-associative.
expr \| expr
Returns the evaluation of the first expr if it is nei-
ther 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 coal-
ition 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 arguments.
expr : expr
The matching operator : (colon) compares the first
argument with the second argument, which must be an
internationalized basic regular expression (BRE). See
regex(5) and NOTES. Normally, the /usr/bin/expr match-
ing 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.
integer
An argument consisting only of an (optional) unary
minus followed by digits.
string
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.
EXAMPLES
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 $a equal to either
/usr/abc/file or just file, the example returns file. (Watch
out for / alone as an argument: expr takes it as the divi-
sion operator. See NOTES below.)
example$ expr $a : '.*/\(.*\)' \| $a
Example 3: Using // characters to simplify the expression
Here is a better version of the previous example. The addi-
tion of the // characters eliminates any ambiguity about the
division operator and simplifies the whole expression.
example$ expr //$a : '.*/\(.*\)'
/usr/bin/expr
Example 4: Returning the number of bytes in a variable
example$ expr "$VAR" : '.*'
/usr/xpg4/bin/expr
Example 5: Returning the number of characters in a variable
example$ expr "$VAR" : '.*'
ENVIRONMENT VARIABLES
See environ(5) 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:
0 If the expression is neither NULL nor 0.
1 If the expression is either NULL or 0.
2 For invalid expressions.
>2 An error occurred.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
| CSI | enabled |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
SEE ALSO
basename(1), ed(1), sh(1), Intro(3), attributes(5),
environ(5), regex(5), standards(5)
DIAGNOSTICS
syntax error
Operator and operand errors.
non-numeric argument
Arithmetic is attempted on such a string.
NOTES
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(5) manual page.
Man(1) output converted with
man2html