106 lines
2.8 KiB
Groff
106 lines
2.8 KiB
Groff
.\" $NetBSD: expr.1,v 1.10 1997/10/20 08:51:56 enami Exp $
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.\"
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.\" Written by J.T. Conklin <jtc@netbsd.org>.
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.\" Public domain.
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.\"
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.Dd July 3, 1993
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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 & 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 "{=, >, >=, <, <=, !=}" 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. 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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.Sh EXAMPLES
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.Bl -enum
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.It
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The following example adds one to the variable a.
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.Dl a=`expr $a + 1`
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.It
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The following example returns the filename portion of a pathname stored
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in variable a. The // characters act to eliminate ambiguity with the
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division operator.
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.Dl expr "//$a" Li : '.*/\e(.*\e)'
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.It
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The following example returns the number of characters in variable a.
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.Dl expr $a Li : '.*'
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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 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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.El
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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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