Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original documentation from The Open Group can be obtained online at
http://www.opengroup.org/bookstore/.
The Institute of Electrical and Electronics Engineers and The Open
Group, have given us permission to reprint portions of their
documentation.
In the following statement, the phrase ``this text'' refers to portions
of the system documentation.
Portions of this text are reprinted and reproduced in electronic form
in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,
Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6,
Copyright (C) 2001-2004 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy
between these versions and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html.
This notice shall appear on any product containing this material.
The contents of this file are subject to the terms of the
Common Development and Distribution License (the "License").
You may not use this file except in compliance with the License.
You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
or http://www.opensolaris.org/os/licensing.
See the License for the specific language governing permissions
and limitations under the License.
When distributing Covered Code, include this CDDL HEADER in each
file and include the License file at usr/src/OPENSOLARIS.LICENSE.
If applicable, add the following below this CDDL HEADER, with the
fields enclosed by brackets "[]" replaced with your own identifying
information: Portions Copyright [yyyy] [name of copyright owner]
Copyright 1989 AT&T
Portions Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.
Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved
/usr/bin/expr argument...
/usr/xpg4/bin/expr argument...
/usr/xpg6/bin/expr argument...
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 \e| 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.
Returns the first expr if neither expr is NULL or 0, otherwise returns 0.
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.
Addition or subtraction of integer-valued arguments.
Multiplication, division, or remainder of the integer-valued arguments.
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(5) 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 [\e(...\e)], the matching operator returns the string corresponding to \e1.
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 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.
Return the length (that is, the number of bytes) of string.
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 : '.*/\e(.*\e)' \e| $a
Example 3 Using // characters to simplify the expression
Here is a better version of the previous example. The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression.
example$ expr //$a : '.*/\e(.*\e)'
Example 4 Returning the number of bytes in a variable
example$ expr "$VAR" : '.*'
Example 5 Returning the number of characters in a variable
example$ expr "$VAR" : '.*'
See environ(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.
As a side effect of expression evaluation, expr returns the following exit values: 0
If the expression is neither NULL nor 0.
If the expression is either NULL or 0.
For invalid expressions.
An error occurred.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| CSI enabled |
| Interface Stability Standard |
basename(1), ed(1), sh(1), Intro(3), attributes(5), environ(5), regex(5), standards(5)
Operator and operand errors.
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=
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.