157 lines
3.7 KiB
Groff
157 lines
3.7 KiB
Groff
.\" $OpenBSD: src/bin/expr/expr.1,v 1.22 2014/02/23 18:13:27 schwarze Exp $
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.\" $NetBSD: expr.1,v 1.9 1995/04/28 23:27:13 jtc 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 $Mdocdate: September 3 2010 $
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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 expr
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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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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 | 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
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integer-valued arguments.
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.It Ar expr1 Li : Ar expr2
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The
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.Ql \&:
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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 basic regular expression.
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The regular expression is anchored
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to the beginning of the string with an implicit
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.Ql ^ .
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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, returns 0.
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.Pp
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Note: the empty string cannot be matched using
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.Bd -literal -offset indent
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expr '' : '$'
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.Ed
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.Pp
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This is because the returned number of matched characters
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.Pq zero
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is indistinguishable from a failed match, so
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.Nm
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returns failure
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.Pq 0 .
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To match the empty string, use a structure such as:
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.Bd -literal -offset indent
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expr X'' : 'X$'
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.Ed
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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 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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.Pp
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.Bl -tag -width Ds -offset indent -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 \*(Gt2
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An error occurred (such as memory allocation failure).
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.El
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.Sh EXAMPLES
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Add 1 to the variable
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.Va a :
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.Bd -literal -offset indent
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$ a=`expr $a + 1`
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.Ed
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.Pp
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Return the filename portion of a pathname stored
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in variable
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.Va a .
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The
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.Ql //
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characters act to eliminate ambiguity with the division operator:
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.Bd -literal -offset indent
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$ expr "//$a" \&: '.*/\e(.*\e)'
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.Ed
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.Pp
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Return the number of characters in variable
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.Va a :
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.Bd -literal -offset indent
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$ expr $a \&: '.*'
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.Ed
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.Sh SEE ALSO
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.Xr test 1 ,
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.Xr re_format 7
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.Sh STANDARDS
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The
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.Nm
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utility is compliant with the
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.St -p1003.1-2008
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specification.
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.Sh HISTORY
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The
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.Nm
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utility first appeared in the Programmer's Workbench (PWB/UNIX)
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and has supported regular expressions since
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.At v7 .
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It was rewritten from scratch for
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.Bx 386 0.1
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and again for
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.Nx 1.1 .
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.Sh AUTHORS
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.An -nosplit
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The first free version was written by
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.An Pace Willisson
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in 1992.
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This version was written by
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.An John T. Conklin
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in 1994.
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