sbase/expr.1

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.Dd 2015-10-08
.Dt EXPR 1
.Os sbase
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.Sh NAME
.Nm expr
.Nd evaluate expression
.Sh SYNOPSIS
.Nm
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.Ar expression
.Sh DESCRIPTION
.Nm
evaluates
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.Ar expression
and writes the result to stdout.
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.Pp
There are two elemental expressions,
.Sy integer
and
.Sy string.
Let
.Sy expr
be a non-elemental expression and
.Sy expr1 ,
.Sy expr2
arbitrary expressions.
Then
.Sy expr
has the recursive form
.Sy expr = [(] expr1 operand expr2 [)].
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.Pp
With
.Sy operand
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being in order of increasing precedence:
.Bl -tag -width Ds
.It |
Evaluate to
.Sy expr1
if it is neither an empty string nor 0; otherwise evaluate to
.Sy expr2 .
.It &
Evaluate to
.Sy expr1
if
.Sy expr1
and
.Sy expr2
are neither empty strings nor 0; otherwise evaluate to 0.
.It = > >= < <= !=
If
.Sy expr1
and
.Sy expr2
are integers, evaluate to 1 if the relation is true and 0 if it is false.
If
.Sy expr1
and
.Sy expr2
are strings, apply the relation to the return value of
.Xr strcmp 3 .
.It + -
If
.Sy expr1
and
.Sy expr2
are integers, evaluate to their sum or subtraction.
.It * / %
If
.Sy expr1
and
.Sy expr2
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are integers, evaluate to their multiplication, division or remainder.
.It :
Evaluate to the number of characters matched in
.Sy expr1
against
.Sy expr2 . expr2
is anchored with an implicit '^'.
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.Pp
You can't directly match the empty string, since zero matched characters
resolve equally to a failed match.
To work around this limitation, use "expr X'' : 'X$' instead of "expr ''
: '$'"
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.El
.Sh EXIT STATUS
.Bl -tag -width Ds
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.It 0
.Ar expression
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is neither an empty string nor 0.
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.It 1
.Ar expression
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is an empty string or 0.
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.It 2
.Ar expression
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is invalid.
.It > 2
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An error occurred.
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.El
.Sh SEE ALSO
.Xr test 1
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.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2013
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specification.