.\" -*- nroff -*-
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.\" Copyright (c) 1993 Winning Strategies, Inc.
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.\" $FreeBSD: src/bin/expr/expr.1,v 1.9.2.4 2003/05/16 22:55:19 keramida Exp $
.\" $DragonFly: src/bin/expr/expr.1,v 1.2 2003/06/17 04:22:50 dillon Exp $
.\"
.Dd May 10, 2002
.Dt EXPR 1
.Os
.Sh NAME
.Nm expr
.Nd evaluate expression
.Sh SYNOPSIS
.Nm
.Ar expression
.Sh DESCRIPTION
The
.Nm
utility evaluates
.Ar expression
and writes the result on standard output.
.Pp
All operators and operands must be passed as separate arguments.
Several of the operators have special meaning to command interpreters
and must therefore be quoted appropriately.
All integer operands are interpreted in base 10.
.Pp
Arithmetic operations are performed using signed integer math.
.Pp
Operators are listed below in order of increasing precedence; all
are left-associative.
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 SEE ALSO
.Xr sh 1 ,
.Xr test 1
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.2 .