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 inter‐
face: 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 other‐
wise.
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. 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
/ (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 number, in bits.
bits (1) (mpexpr only). Push the size, in bits, of the argument.
expmod, invert (2)
(mpexpr only). See keyring-ipint(2).
exp, xx, ** (mpexpr only). Exponentiation.
SOURCE
/appl/cmd/sh/expr.b
SEE ALSOsh(1), sh-std(1), sh-tk(1), keyring-ipint(2)BUGS
Postfix notation can be confusing. Any operators that contain shell
metacharacters (e.g. ``*'', ``>'') must be quoted to avoid interpreta‐
tion by the shell. Base64 notation can contain # characters, which
need quoting to avoid interpretation by the shell.
SH-EXPR(1)
