.TH DERP 1
.SH NAME
derp \- directory-examining recursive compare
.SH SYNOPSIS
.B derp
[
.B -qcutDL
] [
.B -p
.I perms
] 
.I myfile
.I oldfile
.I yourfile
.SH DESCRIPTION
.I Derp
recursively compares the two directories
.I myfile
and
.I yourfile
using a third common backup directory
.I oldfile
as reference. The changes found are printed
to standard output, one per line, with the file
status describing either side followed by tabulator
and the relative file path.
.LP
The possible status codes:
.TP
.B an
File added in
.I myfile
.TP
.B na
File added in
.I yourfile
.TP
.B aa!
Both sides added different files with the
same name
.TP
.B mn
File was modified in
.I myfile
.TP
.B nm
File was modified in
.I yourfile
.TP
.B mm!
File was changed differently in
.I myfile
and
.I yourfile
.TP
.B dn
File was deleted in
.I myfile
.TP
.B nd
File was deleted in
.I yourfile
.TP
.B md!
File was modified in
.I myfile
but deleted in
.I yourfile
.TP
.B dm!
File was modified in
.I yourfile
but deleted in
.I myfile
.LP
Errors are printed to standard error unless
.B -q
option is specified. The program is terminated
when errors are encountered unless the
.B -c
option is given. This can be useful if files
are not accessible due to file permission or
media corruption.
.PP
The
.B -u
option will consider changes of file owner and group.
When omitted, file ownership is ignored.
.PP
The
.B -p
option sets the octal mask
.I perms
of bits to check in the file permissions. The default
ignores file permissions.
.PP
When modification times are comparable then the
.B -t
option can be used to quickly find changes. If specified,
files are considered unchanged if the name, file size and
the modification time matches. This is useful when
comparing /n/dump archives on the same fileserver.
.PP
Files are considered the same if they are from the
same mount and their
.B qid
(see
.IR stat (5))
matches. For directories, the access time is also
compared. If the access time was disabled on the
fileserver, then all directories need to be compared
using the
.B -D
option.
.PP
Some filesystems like
.IR hgfs (4)
do not always return exact file size in stat, so
the length check can be disabled with the
.B -L
option.
.SH SOURCE
.B /sys/src/cmd/derp.c
.SH "SEE ALSO"
.IR cmp (1),
.IR diff (1),
.IR history (1),
.IR fs (4),
.IR hgfs (4)
.SH DIAGNOSTICS
The exit status is set to 'errors' when
errors were encountered.