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EXPR(1)			     BSD Reference 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. Charac-
     ters 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 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
	     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 be-
	     ginning 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, returns 0.

	     Note: the empty string cannot be matched using

		   expr '' : '$'

	     This is because the returned number of matched characters (zero)
	     is indistinguishable from a failed match, so expr returns failure
	     (0). To match the empty string, use a structure such as:

		   expr X'' : 'X$'

     Parentheses are used for grouping in the usual manner.

EXAMPLES
     $ a=`expr $a + 1`

     Add 1 to the variable a.

     $ expr //$a : '.*/\(.*\)'

     Return the filename portion of a pathname stored in variable a. The '//'
     characters act to eliminate ambiguity with the division operator.

     $ expr $a : '.*'

     Return the number of characters in variable 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.
     >2	     An error occurred (such as memory allocation failure).

SEE ALSO
     test(1)

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

MirOS BSD #10-current		 July 3, 1993				     1
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