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EXPR(1)			  BSD 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.

     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
     symbols ‘{’ and ‘}’.

     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
	     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 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
     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 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.

ENVIRONMENT
     EXPR_COMPAT  If set, enables 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
     ·	 The following example (in sh(1) syntax) adds one to the variable a:
	       a=$(expr $a + 1)

     ·	 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)

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

     ·	 With shell arithmetic, no escaping is required:
	       a=$((a + 1))

     ·	 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" : '.*/\(.*\)'

     ·	 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.

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

     ·	 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 1003.1-2001 (“POSIX.1”), provided
     that compatibility mode is not enabled.  The -e flag is an extension.

BSD			       September 9, 2010			   BSD
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