How to modify file's date programmaticaly? [closed] - linux

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I have some image files with the wrong date (date of file creation, the value that is shown by ls -l), because it was set wrong in the camera. How can I increment the date by two days in a script changing all *.jpg files in a directory? Bash, Perl, what ever runs on a Linux machine and is appropriate for the job would be fine.
Searching the web I found that touch is used to manipulate date, but I did not found a way incrementing it by two days, while preserving the time.
Thank you.

Answer 1

I guess that instead of modifying the date of the file (like all other responses #this time), you would like to modify the metadatas, so see this page : http://savvyadmin.com/fixing-dates-in-image-exif-tag-data-from-linux/
you have to use jhead (or exiv2) like this :
jhead -ts2003:01:01-00:00:00 image.jpg
Last but not least, there's a special switch -ta to modify directly the date : ex. for 2 days later :
for i in *.jpg; do jhead -ta+48:00 "$i"; done

Answer 2

Use touch to change modtime.
Use date to operate on the date.
Untested:
for f in *jpg; do
mtime=`date -r $f`
nextt=`date "$mtime + 2 days"`
touch -d "$nextt" $f
done

Answer 3

touch is the tool for the job.
for file in P123*.JPG ; do
touch --date="$(date -r $file) + 2 days" $file
done