f769c2402f
- sort references in SEE ALSO section to section number, name. - cols.1: proper order of sections. - wrap lines to max 79 column length.
104 lines
1.7 KiB
Groff
104 lines
1.7 KiB
Groff
.Dd January 25, 2015
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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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.Nm
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evaluates
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.Ar expression
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and writes the result to stdout.
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.Pp
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There are two elemental expressions,
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.Sy integer
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and
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.Sy string.
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Let
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.Sy expr
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be a non-elemental expression and
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.Sy expr1 ,
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.Sy expr2
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arbitrary expressions. Then
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.Sy expr
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has the recursive form
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.Sy expr = [(] expr1 operand expr2 [)].
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.Pp
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With
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.Sy operand
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being in oder of increasing precedence:
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.Bl -tag -width Ds
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.It |
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Evaluate to
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.Sy expr1
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if it is neither an empty string nor 0; otherwise evaluate to
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.Sy expr2 .
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.It &
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Evaluate to
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.Sy expr1
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if
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.Sy expr1
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and
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.Sy expr2
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are neither empty strings nor 0; otherwise evaluate to 0.
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.It = > >= < <= !=
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If
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.Sy expr1
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and
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.Sy expr2
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are integers, evaluate to 1 if the relation is true and 0 if it is false.
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If
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.Sy expr1
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and
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.Sy expr2
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are strings, apply the relation to the return value of
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.Xr strcmp 3 .
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.It + -
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If
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.Sy expr1
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and
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.Sy expr2
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are integers, evaluate to their sum or subtraction.
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.It * / %
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If
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.Sy expr1
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and
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.Sy expr2
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are integers, evaluate to their mulitplication, division or remainder.
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.It :
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Evaluate to the number of characters matched in
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.Sy expr1
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against
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.Sy expr2 . expr2
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is anchored with an implicit '^'.
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.Pp
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You can't directly match the empty string, since zero matched characters
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resolve equally to a failed match. To work around this limitation, use
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"expr X'' : 'X$' instead of "expr '' : '$'"
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.El
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.Sh EXIT STATUS
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.Bl -tag -width Ds
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.It 0
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.Ar expression
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is neither an empty string nor 0
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.It 1
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.Ar expression
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is an empty string or 0
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.It 2
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.Ar expression
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is invalid
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.It > 2
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An error occured
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.El
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.Sh SEE ALSO
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.Xr test 1
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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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