NAME

expr, ntest - shell module for simple arithmetic.

SYNOPSIS

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

DESCRIPTION

Expr is a loadable module for sh(1) that provides support for simple integer arithmetic. It provides one 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) metacharacters. All operations use 64-bit signed integers; 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 output base for numbers yielded by expr. 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. The operators supported by expr are as follows (the number of operands required in is given parentheses):

+(2)

Addition

-(2)

Subtraction

x,*(2)

Multiplication

/(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.

SOURCE

/appl/cmd/sh/expr.b

SEE ALSO

sh(1), sh-std(1), sh-tk(1)

BUGS

Postfix notation can be confusing. Any operators that contain shell metacharacters (e.g. ``*'', ``>'') must be quoted to avoid interpretation by the shell.

SH-EXPR(1)

Rev:  Fri Mar 31 10:28:24 GMT 2006