freebsd-dev/bin/expr/expr.1

.\" -*- nroff -*-
.\"
.\" Copyright (c) 1993 Winning Strategies, Inc.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"      This product includes software developed by Winning Strategies, Inc.
.\" 4. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\"	$Id: expr.1,v 1.6 1997/02/22 14:03:37 peter Exp $
.\"
.Dd July 3, 1993
.Dt EXPR 1
.Os
.Sh NAME
.Nm expr
.Nd evaluate expression
.Sh SYNOPSIS
.Nm expr
.Ar expression
.Sh DESCRIPTION
The
.Nm
utility evaluates 
.Ar expression
and writes the result on standard output.
.Pp
All operators are separate arguments to the
.Nm
utility.
Characters special to the command interpreter must be escaped.
.Pp
Operators are listed below in order of increasing precedence.
Operators with equal precedence are grouped within { } symbols.
.Bl -tag -width indent
.It Ar expr1 Li | Ar expr2
Return the evaluation of 
.Ar expr1 
if it is neither an empty string nor zero;
otherwise, returns the evaluation of
.Ar expr2 .
.It Ar expr1 Li & Ar expr2
Return the evaluation of
.Ar expr1
if neither expression evaluates to an empty string or zero;
otherwise, returns zero.
.It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
Return the results of integer comparison if both arguments are integers; 
otherwise, returns the results of string comparison using the locale-specific
collation sequence.
The result of each comparison is 1 if the specified relation is true,
or 0 if the relation is false.
.It Ar expr1 Li "{+, -}" Ar expr2
Return the results of addition or subtraction of integer-valued arguments.
.It Ar expr1 Li "{*, /, %}" Ar expr2
Return the results of multiplication, integer division, or remainder of integer-valued arguments.
.It Ar expr1 Li : Ar expr2
The 
.Dq \:
operator matches 
.Ar expr1 
against 
.Ar expr2 ,
which must be a regular expression.  The regular expression is anchored
to the beginning of  the string with an implicit 
.Dq ^ .
.Pp
If the match succeeds and the pattern contains at least one regular
expression subexpression 
.Dq "\e(...\e)" , 
the string corresponding to 
.Dq "\e1"
is returned;
otherwise the matching operator returns the number of characters matched. 
If the match fails and the pattern contains a regular expression subexpression
the null string is returned;
otherwise 0.
.El
.Pp
Parentheses are used for grouping in the usual manner.
.Sh EXAMPLES
.Bl -enum
.It 
The following example adds one to the variable a.
.Dl a=`expr $a + 1`
.It
The following example returns the filename portion of a pathname stored
in variable a.  The // characters act to eliminate ambiguity with the
division operator.
.Dl expr "//$a" Li : '.*/\e(.*\e)'
.It
The following example returns the number of characters in variable a.
.Dl expr $a Li : '.*'
.El
.Sh DIAGNOSTICS
The
.Nm
utility exits with one of the following values:
.Bl -tag -width indent -compact
.It 0
the expression is neither an empty string nor 0.
.It 1
the expression is an empty string or 0.
.It 2
the expression is invalid.
.El
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.2 .