.TH LUHNCHECK 1 LUHNCHECK

.SH NAME
luhncheck \- Check number with Luhn's algorithm

.SH SYNOPSIS
.B luhncheck
.IR number " ..."

.SH DESCRIPTION
The
.B luhncheck
utility checks that a number, containing a check digit,
is valid according to Luhn's algorithm.

.SH OPTIONS
The
.B luhncheck
utility conforms to the Base Definitions volume of POSIX.1-2017,
.IR "Section 12.2" ,
.IR "Utility Syntax Guidelines" .
.PP
No options are supported.

.SH OPERANDS
The following operand is supported:
.TP
.I number
Number to check.

.SH STDIN
Not used.

.SH INPUT FILES
None.

.SH ENVIRONMENT VARIABLES
No environment variables affect the execution of
.BR luhncheck .

.SH ASYNCHRONOUS EVENTS
Default.

.SH STDOUT
The
.B luhncheck
utility will print one line per
.IR number ,
in the order they are provided in the command line,
to the standard output.
Each line will be use the format

.RS
.B \(dq%s is %s\en\(dq,
.IB number ,
.RI < \fB\(dqOK\(dq\fP\ if\ valid,\ \fB\(dqinvalid\(dq\fP\ otherwise >.
.RE

.SH STDERR
The standard error is only used for diagnostic messages.

.SH OUTPUT FILES
None.

.SH EXTENDED DESCRIPTION
None.

.SH EXIT STATUS
The following exit values are returned:
.TP
0
All
.IR number s
are valid.
.TP
1
At least one
.I number
is invalid.
.TP
2
An error occured.

.SH SEE ALSO
.BR gluhncheck (1)