[CentOS] Opposite of cp -u

[Adam Thompson]

CentOS mailing list <centos at centos.org> writes:
>I had at one point copied a large number of files between drives and
>did 
>not use the -p and thus the timestamps were all set to the date of the
>copy.
>
>I did not catch this, and deleted the source.  So I 'lived' with it
>and 
>have since changed many files.
>
>Well, yesterday I found a good backup of many of those files and I
>want 
>to restore them to their proper dates.
>
>cp -p -u is exactly the opposite of what I want.  I want to copy only
>if 
>the source files have an earlier date than the destination files.
>
>The source files are just an old copy on another drive that I found
>when 
>cleaning up things...
>

SRC=/my/restored/files
DST=/the/working/tree
export SRC DST
find "$SRC" -type f -print | while read A; do [ "${A}" -ot
"${DST}${A##$SRC}" ] && /bin/touch -r ${A} "${DST}${A##$SRC}"; done

Note that using this syntax, the two variables cannot be set in-place
on the same command line as "find ..."; it only seems to work for me if
they're exported as environment variables.

A more expanded version of the same, with commentary:

cat > fix_timestamps.sh << __EOF__
#!/bin/sh
### Scans a source directory for files, setting the dates of same-named
files in a target directory
### Adam Thompson <athompson at sjsd.net> 2007-Aug-07
# Source directory - no need for trailing slash
SRC=/my/restored/files
# Target directory - no need for trailing slash
DST=/the/working/tree
# Locate all _files_ only
find "$SRC" -type f -print | (	# subshell not necessary, only here for
readability
	# read each line of input from the pipe into $A
	while read A; do 
	# if's can be shortened to && most times
	# Proceed only if source file is OlderThan target file
	if [ "${A}" -ot "${DST}${A##$SRC}" ]; then
		# Proceed only if target file exists
		# Probably being paranoid, since -ot should have already failed...
		if [ -f  "${DST}${A##$SRC}" ]; then
			# Use "touch" to reset the timestamp on the file \
			#   instead of re-copying the data
			# "-r" == "--reference", uses the source file's \
			#   timestamp to set the destination file's timestamp
			/bin/touch -r ${A} "${DST}${A##$SRC}"
		fi
	fi
	done
)
__EOF__


Obviously the one-liner above is going to be marginally faster,
especially on slower CPUs, but the difference should be minimal - bash
isn't that much of a CPU hog.

-Adam Thompson
 Divisional IT Department,  St. James-Assiniboia School Division
 150 Moray St., Winnipeg, MB, R3J 3A2
 athompson at sjsd.net / tel: (204) 837-5886 x222 / fax: (204) 885-3178

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