268 lines
6.8 KiB
Groff
268 lines
6.8 KiB
Groff
.\" $NetBSD: expr.1,v 1.33 2012/08/12 17:27:04 wiz Exp $
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.\"
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.\" Copyright (c) 2000,2003 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by J.T. Conklin <jtc@NetBSD.org> and Jaromir Dolecek <jdolecek@NetBSD.org>.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd April 20, 2004
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.Dt EXPR 1
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.Os
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.Sh NAME
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.Nm expr
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.Nd evaluate expression
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.Sh SYNOPSIS
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.Nm
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.Ar expression
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.Sh DESCRIPTION
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The
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.Nm
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utility evaluates
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.Ar expression
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and writes the result on standard output.
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.Pp
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All operators are separate arguments to the
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.Nm
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utility.
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Characters special to the command interpreter must be escaped.
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.Pp
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Operators are listed below in order of increasing precedence.
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Operators with equal precedence are grouped within { } symbols.
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.Bl -tag -width indent
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.It Ar expr1 Li \&| Ar expr2
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Returns the evaluation of
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.Ar expr1
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if it is neither an empty string nor zero;
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otherwise, returns the evaluation of
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.Ar expr2 .
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.It Ar expr1 Li \*[Am] Ar expr2
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Returns the evaluation of
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.Ar expr1
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if neither expression evaluates to an empty string or zero;
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otherwise, returns zero.
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.It Ar expr1 Li "{=, \*[Gt], \*[Ge], \*[Lt], \*[Le], !=}" Ar expr2
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Returns the results of integer comparison if both arguments are integers;
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otherwise, returns the results of string comparison using the locale-specific
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collation sequence.
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The result of each comparison is 1 if the specified relation is true,
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or 0 if the relation is false.
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.It Ar expr1 Li "{+, -}" Ar expr2
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Returns the results of addition or subtraction of integer-valued arguments.
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.It Ar expr1 Li "{*, /, %}" Ar expr2
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Returns the results of multiplication, integer division, or remainder of integer-valued arguments.
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.It Ar expr1 Li \&: Ar expr2
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The
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.Dq \&:
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operator matches
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.Ar expr1
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against
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.Ar expr2 ,
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which must be a regular expression.
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The regular expression is anchored
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to the beginning of the string with an implicit
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.Dq ^ .
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.Pp
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If the match succeeds and the pattern contains at least one regular
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expression subexpression
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.Dq "\e(...\e)" ,
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the string corresponding to
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.Dq "\e1"
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is returned;
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otherwise the matching operator returns the number of characters matched.
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If the match fails and the pattern contains a regular expression subexpression
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the null string is returned;
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otherwise 0.
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.It "( " Ar expr No " )"
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Parentheses are used for grouping in the usual manner.
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.El
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.Pp
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Additionally, the following keywords are recognized:
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.Bl -tag -width indent
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.It length Ar expr
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Returns the length of the specified string in bytes.
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.El
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.Pp
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Operator precedence (from highest to lowest):
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.Bl -enum -compact -offset indent
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.It
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parentheses
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.It
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length
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.It
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.Dq \&:
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.It
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.Dq "*" ,
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.Dq "/" ,
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and
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.Dq "%"
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.It
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.Dq "+"
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and
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.Dq "-"
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.It
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compare operators
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.It
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.Dq \*[Am]
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.It
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.Dq \&|
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.El
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.Sh EXIT STATUS
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The
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.Nm
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utility exits with one of the following values:
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.Bl -tag -width Ds -compact
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.It 0
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the expression is neither an empty string nor 0.
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.It 1
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the expression is an empty string or 0.
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.It 2
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the expression is invalid.
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.It \*[Gt]2
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an error occurred (such as memory allocation failure).
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.El
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.Sh EXAMPLES
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.Bl -enum
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.It
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The following example adds one to variable
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.Dq a :
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.Dl a=`expr $a + 1`
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.It
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The following example returns zero, due to subtraction having higher precedence
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than the
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.Dq \*[Am]
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operator:
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.Dl expr 1 '\*[Am]' 1 - 1
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.It
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The following example returns the filename portion of a pathname stored
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in variable
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.Dq a :
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.Dl expr "/$a" Li : '.*/\e(.*\e)'
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.It
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The following example returns the number of characters in variable
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.Dq a :
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.Dl expr $a Li : '.*'
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.El
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.Sh COMPATIBILITY
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This implementation of
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.Nm
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internally uses 64 bit representation of integers and checks for
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over- and underflows.
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It also treats
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.Dq /
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(the division mark) and option
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.Dq --
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correctly depending upon context.
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.Pp
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.Nm
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on other systems (including
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.Nx
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up to and including
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.Nx 1.5 )
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might not be so graceful.
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Arithmetic results might be arbitrarily
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limited on such systems, most commonly to 32 bit quantities.
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This means such
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.Nm
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can only process values between -2147483648 and +2147483647.
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.Pp
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On other systems,
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.Nm
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might also not work correctly for regular expressions where
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either side contains
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.Dq /
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(a single forward slash), like this:
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.Bd -literal -offset indent
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expr / : '.*/\e(.*\e)'
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.Ed
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.Pp
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If this is the case, you might use
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.Dq //
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(a double forward slash)
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to avoid confusion with the division operator:
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.Bd -literal -offset indent
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expr "//$a" : '.*/\e(.*\e)'
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.Ed
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.Pp
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According to
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.St -p1003.2 ,
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.Nm
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has to recognize special option
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.Dq -- ,
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treat it as a delimiter to mark the end of command
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line options, and ignore it.
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Some
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.Nm
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implementations don't recognize it at all; others
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might ignore it even in cases where doing so results in syntax
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error.
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There should be same result for both following examples,
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but it might not always be:
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.Bl -enum -compact -offset indent
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.It
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expr -- : .
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.It
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expr -- -- : .
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.El
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Although
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.Nx
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.Nm
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handles both cases correctly, you should not depend on this behavior
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for portability reasons and avoid passing a bare
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.Dq --
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as the first
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argument.
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.Sh STANDARDS
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The
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.Nm
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utility conforms to
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.St -p1003.2 .
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The
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.Ar length
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keyword is an extension for compatibility with GNU
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.Nm .
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.Sh AUTHORS
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Original implementation was written by
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.An J.T. Conklin
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.Aq jtc@NetBSD.org .
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It was rewritten for
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.Nx 1.6
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by
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.An Jaromir Dolecek
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.Aq jdolecek@NetBSD.org .
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.Sh NOTES
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The empty string
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.Do Dc
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cannot be matched with the intuitive:
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.Bd -literal -offset indent
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expr '' : '$'
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.Ed
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.Pp
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The reason is that the returned number of matched characters (zero)
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is indistinguishable from a failed match, so this returns failure.
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To match the empty string, use something like:
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.Bd -literal -offset indent
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expr x'' : 'x$'
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.Ed
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