SH-EXPR(1) SH-EXPR(1)
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.
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 metacharac-
ters. All operations use 64-bit signed integers; integers
are given in the same form acceptable to Limbo. The rela-
tional operators yield either 1 (true) or 0 (false). If the
-r option is given, radix specifies an output base for num-
bers yielded by expr. Numbers are printed in a form suit-
able 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.
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SH-EXPR(1) SH-EXPR(1)
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.
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