How do I use "touch -t" to shift a batch of JPG timestamps by one hour?

Question

I'm trying to use "touch -t" to shift a batch of JPG created/modified timestamps by one hour to fix a time zone error. Is this possible?
(I don't want to have to manually go to every file, and enter its current timestamp all the same way except for the month.)
By the way, does using the "touch" command have the same JPG lossy effect as saving the file again?

Answer 1

picky picky picky
So you write a script that uses stat to get the current modification time and then add 60 minutes to it, with the date command, then then use that with touch against the file. Nothing to it
#!/bin/sh
find starting.directory -name "*.jpg" | while read file
do
ls -l "$file"
mtimeinsec=$(stat -f %m "$file")
mtimeplus_1H_in_touchfmt=$(date -j -r $mtimeinsec -v +1H +%G%m%d%H%M.%S)
/usr/bin/touch -t $mtimeplus_1H_in_touchfmt "$file"
ls -l "$file"
done
I've added an hour to the modification time. If you want to subtract an hour the +1H to -1H
If you want to use shell wildcard selection modify the loop to be something like
#!/bin/sh
for file in *.jpg
do
... the guts of the above while loop ...
done
If you just want to provide a list of files, you can change the *.jpg to a list of files. JUST BE CAREFUL OF SPACES IN FILE NAMES and directories
If you want a drag and drop application, you can do that with some additional changes and either using Applications -> Automator with the "Run Shell Command" or using Platypus (free download, and a very nice utility). The script would change to:
#!/bin/sh
for file in "$@"
do
... the guts of the above while loop ...
done
I have tested the very first script. I am fairly confident my 2nd to examples are right, but they are untested, so your mileage may vary.