145 lines
3.7 KiB
Groff
145 lines
3.7 KiB
Groff
.\" $NetBSD: expr.1,v 1.14 2000/09/19 17:20:00 jdolecek 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 September 18, 2000
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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 $a + 1`
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.It
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The following example returns the filename portion of a pathname stored
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in variable a.
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.Dl expr "/$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 EXIT STATUS
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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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.It >2
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an error occurred (such as memory allocation failure).
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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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.Sh AUTHOR
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Original implementation was written by
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.An J.T. Conklin Aq jtc@netbsd.org .
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It was rewritten in
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.Nx 1.6
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by
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.An Jaromir Dolecek Aq jdolecek@netbsd.org .
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.Sh BUGS
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This implementation of
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.Nm
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internally uses 64 bit represenation of integers and checks for
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over- and underflows. It also treats / (division mark)
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correctly depending upon context.
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.Pp
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.Nm
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on other systems (including
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.Nx
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up to and including
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.Nx 1.5 )
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might be not so graceful. Arithmetic results might be arbitrarily
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limited on such systems, most commonly to 32 bit quantities.
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This means such
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.Nm
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can only process values between -2147483648 and +2147483647.
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.Pp
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On other systems,
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.Nm
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might also not work correctly for regular expressions where
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either side contains single forward slash, like this:
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.Bd -literal -offset indent
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expr / : '.*/\e(.*\e)'
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.Ed
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.Pp
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If this is the case, you might use // (double forward slash)
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to avoid abiquity with the division operator:
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.Bd -literal -offset indent
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expr "//$a" : '.*/\e(.*\e)'
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.Ed
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