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	expr.1 - sbase - suckless unix tools
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	expr.1 (1768B)
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	1 .Dd October 8, 2015
	2 .Dt EXPR 1
	3 .Os sbase
	4 .Sh NAME
	5 .Nm expr
	6 .Nd evaluate expression
	7 .Sh SYNOPSIS
	8 .Nm
	9 .Ar expression
	10 .Sh DESCRIPTION
	11 .Nm
	12 evaluates
	13 .Ar expression
	14 and writes the result to stdout.
	15 .Pp
	16 There are two elemental expressions,
	17 .Sy integer
	18 and
	19 .Sy string.
	20 Let
	21 .Sy expr
	22 be a non-elemental expression and
	23 .Sy expr1 ,
	24 .Sy expr2
	25 arbitrary expressions.
	26 Then
	27 .Sy expr
	28 has the recursive form
	29 .Sy expr = [(] expr1 operand expr2 [)].
	30 .Pp
	31 With
	32 .Sy operand
	33 being in order of increasing precedence:
	34 .Bl -tag -width Ds
	35 .It \|
	36 Evaluate to
	37 .Sy expr1
	38 if it is neither an empty string nor 0; otherwise evaluate to
	39 .Sy expr2 .
	40 .It &
	41 Evaluate to
	42 .Sy expr1
	43 if
	44 .Sy expr1
	45 and
	46 .Sy expr2
	47 are neither empty strings nor 0; otherwise evaluate to 0.
	48 .It = > >= < <= !=
	49 If
	50 .Sy expr1
	51 and
	52 .Sy expr2
	53 are integers, evaluate to 1 if the relation is true and 0 if it is false.
	54 If
	55 .Sy expr1
	56 and
	57 .Sy expr2
	58 are strings, apply the relation to the return value of
	59 .Xr strcmp 3 .
	60 .It + -
	61 If
	62 .Sy expr1
	63 and
	64 .Sy expr2
	65 are integers, evaluate to their sum or subtraction.
	66 .It * / %
	67 If
	68 .Sy expr1
	69 and
	70 .Sy expr2
	71 are integers, evaluate to their multiplication, division or remainder.
	72 .It :
	73 Evaluate to the number of characters matched in
	74 .Sy expr1
	75 against
	76 .Sy expr2 . expr2
	77 is anchored with an implicit '^'.
	78 .Pp
	79 You can't directly match the empty string, since zero matched characters
	80 resolve equally to a failed match.
	81 To work around this limitation, use "expr X'' : 'X$' instead of "expr ''
	82 : '$'"
	83 .El
	84 .Sh EXIT STATUS
	85 .Bl -tag -width Ds
	86 .It 0
	87 .Ar expression
	88 is neither an empty string nor 0.
	89 .It 1
	90 .Ar expression
	91 is an empty string or 0.
	92 .It 2
	93 .Ar expression
	94 is invalid.
	95 .It > 2
	96 An error occurred.
	97 .El
	98 .Sh SEE ALSO
	99 .Xr test 1
	100 .Sh STANDARDS
	101 The
	102 .Nm
	103 utility is compliant with the
	104 .St -p1003.1-2013
	105 specification.