.\" Copyright (c) 1993 Winning Strategies, Inc.
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.\" $Header: /b/source/CVS/src/bin/expr/expr.1,v 1.1 1993/07/20 20:16:26 jtc 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 expr
utility evaluates 
.Ar expression
and writes the result on standard output.
.Pp
All operators are separate arguments to the
.Nm expr
utility.
Characters special to the command interpreter must be escaped.
.Pp
Operators are listed below in order of increasing precidence.
Operators with equal precidence are grouped within { } symbols.
.Bl -tag -width indent
.It Ar expr1 Li | Ar expr2
Returns 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
Returns the evaluation of
.Ar expr1
if neither expression evaluates to an empty string or zero;
otherwise, returns zero.
.It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
Returns the results of integer comparision if both arguments are integers; 
otherwise, returns the results of lexical comparison.
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
Returns the results of addition or subtraction of integer-valued arguments.
.It Ar expr1 Li "{*, /, %}" Ar expr2
Returns 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 begining of  the string with an invisible 
.Dq ^ ,
therefore
.Dq ^
is not a special character.
.Pp
If the pattern contains at lest 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. 
.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 expr 
utility exits with one of the following values:
.Bl -tag -width Ds
.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 expr
utility
is expected to be 
.St -p1003.2
compatible.