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EXPR(1)			FreeBSD	General	Commands Manual		       EXPR(1)

NAME
     expr -- evaluate expression

SYNOPSIS
     expr [-e] expression

DESCRIPTION
     The expr utility evaluates	expression and writes the result on standard
     output.

     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	and must consist of only an optional leading minus sign	fol-
     lowed by one or more digits (unless less strict parsing has been enabled
     for backwards compatibility with prior versions of	expr in	FreeBSD).

     Arithmetic	operations are performed using signed integer math with	a
     range according to	the C intmax_t data type (the largest signed integral
     type available).  All conversions and operations are checked for over-
     flow.  Overflow results in	program	termination with an error message on
     stdout and	with an	error status.

     The -e option enables backwards compatible	behaviour as detailed below.

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

     expr1 | expr2
	     Return the	evaluation of expr1 if it is neither an	empty string
	     nor zero; otherwise, returns the evaluation of expr2 if it	is not
	     an	empty string; otherwise, returns zero.

     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
	     using 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
	     arguments.

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

     expr1 : expr2
	     The ``:'' operator	matches	expr1 against expr2, which must	be a
	     basic 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 correspond-
	     ing 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
     argument 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 backwards 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 backwards compatibility mode also
     implicitly	enables	the -e option, since this matches the historic behav-
     ior of expr in FreeBSD. This option makes number parsing less strict and
     permits leading white space and an	optional leading plus sign.  In	addi-
     tion, empty operands have an implied value	of zero	in numeric context.
     For historical reasons, defining the environment variable EXPR_COMPAT
     also enables backwards compatibility mode.

ENVIRONMENT
     EXPR_COMPAT  If set, enables backwards compatibility mode.

EXIT STATUS
     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.

EXAMPLES
     +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	 With shell arithmetic,	no escaping is required:
	       a=$((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" : '.*/\(.*\)'

     +o	 With modern sh(1) syntax,
	       "${a##*/}"
	 expands to the	same value.

     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, and a might be interpreted	as an
     operator.

     +o	 To deal with all of this, a complicated command is required:
	       expr \( "X$a" : ".*" \) - 1

     +o	 With modern sh(1) syntax, this	can be done much more easily:
	       ${#a}
	 expands to the	required number.

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

STANDARDS
     The expr utility conforms to IEEE Std 1003.1-2008 (``POSIX.1''), provided
     that backwards compatibility mode is not enabled.

     Backwards compatibility mode performs less	strict checks of numeric argu-
     ments:

     +o	 An empty operand string is interpreted	as 0.

     +o	 Leading white space and/or a plus sign	before an otherwise valid pos-
	 itive numeric operand are allowed and will be ignored.

     The extended arithmetic range and overflow	checks do not conflict with
     POSIX's requirement that arithmetic be done using signed longs, since
     they only make a difference to the	result in cases	where using signed
     longs would give undefined	behavior.

     According to the POSIX standard, the use of string	arguments length,
     substr, index, or match produces undefined	results.  In this version of
     expr, these arguments are treated just as their respective	string values.

     The -e flag is an extension.

FreeBSD	9.2		       February	25, 2012		   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | EXIT STATUS | EXAMPLES | SEE ALSO | STANDARDS

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