.TH XS 8
.CT 1 sa_nonmortals
.SH NAME
xs \- checksums
.SH SYNOPSIS
.B xs 
[
-s
]
[
-k
.I keystring
]
[
-f
.I official-list
]
.IR file ...
.SH DESCRIPTION
.I Xs
computes and reports
checksums of named files,
one report per line, in the form
.IP
filename s1 s2 s3 s4
.LP
where the checksum comprises four groups of four hex digits each.
The checksum algorithm may be perturbed by specifying a
.I keystring
argument.
The
.B -s
argument causes the file's mode, label, owner and group
to enter into the checksum calculation.
.PP
The 
.B -f
argument causes
.I xs
to verify checksums of files against
values
given
in the 
.I official-list
file, which has the format of the output of an earlier 
.I xs
run:
lines consisting of
one file name followed by four groups of hex digits per line.
Text after a
.L #
sign is ignored.
.PP
The checksum algorithm used is meant to be secure: to create a file
whose checksum agrees with that of another given file is very difficult.
.SH EXAMPLES
.EX
xs -s `find /bin -print` | xs /dev/stdin
.EE
.IP
This should return a different value if 
.B /bin
changes in any way.