SH-EXPR(1)                                             SH-EXPR(1)

     NAME
          expr, ntest, mpexpr - shell module for simple arithmetic.

     SYNOPSIS
          load expr OR load mpexpr

          ${expr [ -r radix ] [ arg... ] }
          ntest num

     DESCRIPTION
          Expr and mpexpr are loadable modules for sh(1) that provide
          support for integer arithmetic.  Expr uses 64-bit signed
          integers; mpexpr uses arbitrary-precision signed integers.
          They each provide the same interface: a command ntest, which
          performs a simple boolean test on its integer argument, and
          the substitution operator expr, which takes an expression in
          Reverse Polish notation, and yields its result.

          Ntest returns true if its argument num is non-zero, and
          false otherwise.

          Expr evaluates each arg in turn; if it is an integer it gets
          pushed onto the stack; otherwise it should name one of the
          operators below, whereupon the appropriate number of
          operands are popped off the stack, evaluated as arguments to
          the operator, and the result pushed back onto the stack.
          Arguments are passed to the operator first-pushed first, so,
          for instance, ${expr 2 1 -} yields 1, not -1.  Alternative
          names are given for some operators; this is to avoid the
          necessity of quoting operators that contain sh(1) metachar-
          acters. Integers are given in the same form acceptable to
          Limbo. The relational operators yield either 1 (true) or 0
          (false). If the -r option is given, radix specifies an out-
          put base for printed numbers.  It may be from 2 to 36;
          mpexpr also allows 64 to specify base64 notation.  Numbers
          are printed in a form suitable for re-interpretation by
          expr.

          When all its arguments have been evaluated, expr yields all
          the values remaining on its stack, first pushed first. Note
          that bitwise operators treat their operands as if they were
          stored in two's complement form. The operators supported by
          expr are as follows (the number of operands required in is
          given parentheses).

          + (2)          Addition

          - (2)          Subtraction

          x, * (2)       Multiplication

     SH-EXPR(1)                                             SH-EXPR(1)

          / (2)          Division. Division by zero raises a divide by
                         zero exception.

          % (2)          Modulus. A zero modulus will cause a divide
                         by zero exception to be raised.

          and (2)        Bitwise-and.

          or (2)         Bitwise-or.

          xor (2)        Bitwise-xor.

          ~ (1)          Bitwise-complement..

          _ (1)          Unary minus.

          <<, shl (2)    Shift left.

          >>, shr (2)    Shift right.

          =, ==, eq (2)  Equality.

          !=, neq (2)    Inequality.

          >, gt (2)      Greater than.

          <, lt (2)      Less than.

          <=, le (2)     Less than or equal to.

          >=, ge (2)     Greater than or equal to.

          !, not (1)     Logical negation.

          rep (n)        Rep repeats the last operation (which must
                         have been a two-operand operation other than
                         seq) until the values in the stack are
                         exhausted.

          seq (2)        Seq pushes on the stack a sequence of numbers
                         ranging numerically from its first argument
                         up to and including its second argument. If
                         its second argument is less than its first,
                         the sequence will descend.

          rand (1)       (mpexpr only). Push a secure random number;
                         the argument value gives the size of the num-
                         ber, in bits.

          bits (1)       (mpexpr only). Push the size, in bits, of the
                         argument.

     SH-EXPR(1)                                             SH-EXPR(1)

          expmod, invert (2)
                         (mpexpr only). See keyring-ipint(2).

          exp, xx, **    (mpexpr only). Exponentiation.

     SOURCE
          /appl/cmd/sh/expr.b

     SEE ALSO
          sh(1), sh-std(1), sh-tk(1), keyring-ipint(2)

     BUGS
          Postfix notation can be confusing.  Any operators that con-
          tain shell metacharacters (e.g. ``*'', ``>'') must be quoted
          to avoid interpretation by the shell.  Base64 notation can
          contain # characters, which need quoting to avoid interpre-
          tation by the shell.