NAME
     expr - simple expression evaluator

SYNOPSIS
     expr expression

DESCRIPTION
     Expr parses an expression provided as arguments and prints the result on
     the standard output.

     Expr recognizes three types of operators, relational operators, arith-
     metic operators and string operators.  The following left-associative bi-
     nary operators are listed from lowest to highest precedence:

     |               If the left operand is 0 or the empty string, produce the
                     right operand, otherwise produce the left operand.
     &               If both operands are nonzero and nonempty, produce the
                     left operand; otherwise produce 0.
     <,<=,=,!=,>=,>  If both operands are numbers, produce 1 if the relation
                     holds between the left and right operands, otherwise pro-
                     duce 0.  If one or both operands is not a number, compare
                     operands as ASCII strings and produce 1 if the relation
                     holds, otherwise produce 0.
     +,-             Produce the sum (respectively, difference) of the
                     operands.  Both operands must be numbers.
     *,/,%           Produce the product (respectively, quotient, remainder)
                     of the operands.  Both operands must be numbers.
     :               Match a string (left operand) against a pattern (right
                     operand).  Patterns are ed(1)-style  regular expressions,
                     implicitly anchored to the start of the string.  If the
                     pattern contains matching quoted parentheses, \( and \),
                     then if the string matches the pattern, expr produces the
                     substring which matches the part of the pattern between
                     the parentheses, otherwise it produces the empty string.
                     If the pattern contains no quoted parentheses, expr pro-
                     duces a count of the characters in the string that the
                     pattern matches.

     Expr also permits expressions in parentheses.  Parentheses permit the us-
     er to override precedence.

EXAMPLES
     $ expr 1 + 2
     3
     $ expr 9 / 3 '&' 9 % 2
     3
     $ expr 9 / 3 '&' 9 % 3
     0
     $ expr abcdefg : '[a-e]*'
     5
     $ expr abcdefg : 'a\([a-e]*\)'
     bcde
     $

DIAGNOSTICS
     first operand `%s' to `%s' is not a number
     second operand `%s' to `%s' is not a number
     second operand to `%s' is 0
     out of memory
     error in regular expression: %s
     internal inconsistency in RE prep
     syntax error, last argument was `%s'

SEE ALSO
     bc(1),  sed(1),  test(1)

BUGS
     Many of the operators are special to the shells and have to be quoted.

     Operators can't be used as (string) operands.

     The diagnostic complaints about syntax errors are sometimes quite opaque.