263 lines
7.3 KiB
Groff
263 lines
7.3 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1993 Winning Strategies, Inc.
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.\" All rights reserved.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Winning Strategies, Inc.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 10, 2002
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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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.Op Fl e
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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 and operands must be passed as separate arguments.
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Several of the operators have special meaning to command interpreters
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and must therefore be quoted appropriately.
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All integer operands are interpreted in base 10.
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.Pp
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Arithmetic operations are performed using signed integer math.
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If the
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.Fl e
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flag is specified, arithmetic uses the C
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.Ql intmax_t
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data type (the largest integral type available), and
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.Nm
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will detect arithmetic overflow and return an error indication.
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If a numeric operand is specified which is so large as to overflow
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conversion to an integer, it is parsed as a string instead.
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If
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.Fl e
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is not specified, arithmetic operations and parsing of integer
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arguments will overflow silently according to the rules of the C
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standard, using the
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.Ql long
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data type.
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.Pp
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Operators are listed below in order of increasing precedence; all
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are left-associative.
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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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Return 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 & Ar expr2
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Return 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 "{=, >, >=, <, <=, !=}" Ar expr2
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Return 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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Return the results of addition or subtraction of integer-valued arguments.
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.It Ar expr1 Li "{*, /, %}" Ar expr2
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Return 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 basic 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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.El
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.Pp
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Parentheses are used for grouping in the usual manner.
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.Pp
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Unless the
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.Ev EXPR_COMPAT
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variable is defined in the process environment, this version of
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.Nm
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adheres to the
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.Tn POSIX
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Utility Syntax Guidelines, which require that a leading argument beginning
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with a minus sign be considered an option to the program.
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The standard
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.Ql \&--
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syntax may be used to prevent this interpretation.
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However, many historic implementations of
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.Nm ,
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including the one in previous versions of
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.Fx ,
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will not permit this syntax.
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See the examples below for portable ways to guarantee the correct
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interpretation.
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The
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.Ev EXPR_COMPAT
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variable is intended for use as a transition and debugging aid, when
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.Nm
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is used in complex scripts which cannot easily be recast to avoid the
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non-portable usage.
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Defining
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.Ev EXPR_COMPAT
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also implicitly enables the
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.Fl e
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option, since this matches the historic behavior of
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.Nm
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in
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.Fx .
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.Pp
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The
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.Nm
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utility makes no lexical distinction between arguments which may be
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operators and arguments which may be operands.
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An operand which is lexically identical to an operator will be considered a
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syntax error.
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See the examples below for a work-around.
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.Pp
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The syntax of the
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.Nm
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command in general is historic and inconvenient.
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New applications are advised to use shell arithmetic rather than
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.Nm .
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.Sh ENVIRONMENT
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.Bl -tag -compact -width EXPR_COMPAT
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.It Ev EXPR_COMPAT
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If set,
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.Nm
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will emulate historic
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.Nm
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implementations which did not obey the Utility Syntax Guidelines.
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Implies
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.Fl e .
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.El
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.Sh EXAMPLES
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.Bl -bullet
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.It
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The following example (in
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.Xr sh 1
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syntax) adds one to the variable
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.Va a :
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.Dl a=$(expr $a + 1)
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.It
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This will fail if the value of
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.Va a
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is a negative number.
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To protect negative values of
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.Va a
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from being interpreted as options to the
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.Nm
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command, one might rearrange the expression:
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.Dl a=$(expr 1 + $a)
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.It
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More generally, parenthesize possibly-negative values:
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.Dl a=$(expr \e( $a \e) + 1)
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.It
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This example prints the filename portion of a pathname stored
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in variable
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.Va a .
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Since
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.Va a
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might represent the path
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.Pa / ,
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it is necessary to prevent it from being interpreted as the division operator.
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The
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.Li //
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characters resolve this ambiguity.
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.Dl expr \*q//$a\*q \&: '.*/\e(.*\e)'
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.El
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.Pp
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The following examples output the number of characters in variable
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.Va a .
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Again, if
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.Va a
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might begin with a hyphen, it is necessary to prevent it from being
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interpreted as an option to
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.Nm .
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.Bl -bullet
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.It
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If the
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.Nm
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command conforms to
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.St -p1003.1-2001 ,
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this is simple:
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.Dl expr -- \*q$a\*q \&: \*q.*\*q
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.It
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For portability to older systems, however, a more complicated command
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is required:
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.Dl expr \e( \*qX$a\*q \&: \*q.*\*q \e) - 1
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.El
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.Sh DIAGNOSTICS
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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 indent -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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.El
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr test 1
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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 -p1003.1-2001 ,
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provided that the
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.Ev EXPR_COMPAT
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environment variable is not defined.
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The
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.Fl e
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flag is an extension.
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