expr man page on OpenDarwin

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

NAME
     expr — evaluate expression

SYNOPSIS
     expr expression

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

     All operators are separate arguments to the expr utility.	Characters
     special to the command interpreter must be escaped.

     Operators are listed below in order of increasing precedence.  Operators
     with equal precedence are grouped within { } symbols.

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

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

     expr1 {=, >, >=, <, <=, !=} expr2
	     Returns 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
	     Returns the results of addition or subtraction of integer-valued
	     arguments.

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

     expr1 : expr2
	     The “:” operator matches expr1 against expr2, which must be a
	     regular expression.  The regular expression is anchored to the
	     beginning of  the string with an implicit “^”.  expr expects
	     "basic" regular expressions, see re_format(7) for more informa‐
	     tion on regular expressions.

	     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.

EXAMPLES
     1.	  The following example adds one to the variable a.
		a=`expr $a + 1`

     2.	  The following example returns the filename portion of a pathname
	  stored in variable a.	 The // characters act to eliminate ambiguity
	  with the division operator.
		expr //$a : '.*/\(.*\)'

     3.	  The following example returns the number of characters in variable
	  a.
		expr $a : '.*'

DIAGNOSTICS
     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.

STANDARDS
     The expr utility conforms to IEEE Std 1003.2 (“POSIX.2”).

BSD				 July 3, 1993				   BSD
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