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EXPR(1)			  BSD General Commands Manual		       EXPR(1)

     expr -- evaluate expression

     expr [-e] expression

     The expr utility evaluates	expression and writes the result on standard

     All operators and operands	must be	passed as separate arguments.  Several
     of	the operators have special meaning to command interpreters and must
     therefore be quoted appropriately.	 All integer operands are interpreted
     in	base 10.

     Arithmetic	operations are performed using signed integer math.  If	the -e
     flag is specified,	arithmetic uses	the C intmax_t data type (the largest
     integral type available), and expr	will detect arithmetic overflow	and
     return an error indication.  If a numeric operand is specified which is
     so	large as to overflow conversion	to an integer, it is parsed as a
     string instead.  If -e is not specified, arithmetic operations and	pars-
     ing of integer arguments will overflow silently according to the rules of
     the C standard, using the long data type.

     Operators are listed below	in order of increasing precedence; all are
     left-associative.	Operators with equal precedence	are grouped within { }

     expr1 | expr2
	     Return the	evaluation of expr1 if it is neither an	empty string
	     nor zero; otherwise, returns the evaluation of expr2.

     expr1 & expr2
	     Return the	evaluation of expr1 if neither expression evaluates to
	     an	empty string or	zero; otherwise, returns zero.

     expr1 {=, >, >=, <, <=, !=} expr2
	     Return the	results	of integer comparison if both arguments	are
	     integers; otherwise, returns the results of string	comparison us-
	     ing the locale-specific collation sequence.  The result of	each
	     comparison	is 1 if	the specified relation is true,	or 0 if	the
	     relation is false.

     expr1 {+, -} expr2
	     Return the	results	of addition or subtraction of integer-valued

     expr1 {*, /, %} expr2
	     Return the	results	of multiplication, integer division, or	re-
	     mainder of	integer-valued arguments.

     expr1 : expr2
	     The ":" operator matches expr1 against expr2, which must be a ba-
	     sic regular expression.  The regular expression is	anchored to
	     the beginning of the string with an implicit "^".

	     If	the match succeeds and the pattern contains at least one regu-
	     lar expression subexpression "\(...\)", the string	corresponding
	     to	"\1" is	returned; otherwise the	matching operator returns the
	     number of characters matched.  If the match fails and the pattern
	     contains a	regular	expression subexpression the null string is
	     returned; otherwise 0.

     Parentheses are used for grouping in the usual manner.

     The expr utility makes no lexical distinction between arguments which may
     be	operators and arguments	which may be operands.	An operand which is
     lexically identical to an operator	will be	considered a syntax error.
     See the examples below for	a work-around.

     The syntax	of the expr command in general is historic and inconvenient.
     New applications are advised to use shell arithmetic rather than expr.

   Compatibility with previous implementations
     Unless FreeBSD 4.x	compatibility is enabled, this version of expr adheres
     to	the POSIX Utility Syntax Guidelines, which require that	a leading ar-
     gument beginning with a minus sign	be considered an option	to the pro-
     gram.  The	standard -- syntax may be used to prevent this interpretation.
     However, many historic implementations of expr, including the one in pre-
     vious versions of FreeBSD,	will not permit	this syntax.  See the examples
     below for portable	ways to	guarantee the correct interpretation.  The
     check_utility_compat(3) function (with a utility argument of "expr") is
     used to determine whether compatibility mode should be enabled.  This
     feature is	intended for use as a transition and debugging aid, when expr
     is	used in	complex	scripts	which cannot easily be recast to avoid the
     non-portable usage.  Enabling compatibility mode also implicitly enables
     the -e option, since this matches the historic behavior of	expr in
     FreeBSD.  For historical reasons, defining	the environment	variable
     EXPR_COMPAT also enables compatibility mode.

     EXPR_COMPAT  If set, enables compatibility	mode.

     The expr utility exits with one of	the following values:
     0	     the expression is neither an empty	string nor 0.
     1	     the expression is an empty	string or 0.
     2	     the expression is invalid.

     o	 The following example (in sh(1) syntax) adds one to the variable a:
	       a=$(expr	$a + 1)

     o	 This will fail	if the value of	a is a negative	number.	 To protect
	 negative values of a from being interpreted as	options	to the expr
	 command, one might rearrange the expression:
	       a=$(expr	1 + $a)

     o	 More generally, parenthesize possibly-negative	values:
	       a=$(expr	\( $a \) + 1)

     o	 This example prints the filename portion of a pathname	stored in
	 variable a.  Since a might represent the path /, it is	necessary to
	 prevent it from being interpreted as the division operator.  The //
	 characters resolve this ambiguity.
	       expr "//$a" : '.*/\(.*\)'

     The following examples output the number of characters in variable	a.
     Again, if a might begin with a hyphen, it is necessary to prevent it from
     being interpreted as an option to expr.

     o	 If the	expr command conforms to IEEE Std 1003.1-2001 ("POSIX.1"),
	 this is simple:
	       expr -- "$a" : ".*"

     o	 For portability to older systems, however, a more complicated command
	 is required:
	       expr \( "X$a" : ".*" \) - 1

     sh(1), test(1), check_utility_compat(3)

     The expr utility conforms to IEEE Std 1003.1-2001 ("POSIX.1"), provided
     that compatibility	mode is	not enabled.  The -e flag is an	extension.

BSD				 July 12, 2004				   BSD


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