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
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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.
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SH-EXPR(1) SH-EXPR(1)
expmod, invert (2)
(mpexpr only). See 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.
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