#+TITLE: exiftool.el
#+LINK: wikipedia https://en.wikipedia.org/wiki/
exiftool.el is an elisp wrapper around [[http://www.sno.phy.queensu.ca/~phil/exiftool/][ExifTool]].  ExifTool supports
reading and writing metadata in various formats including [[wikipedia:Exif][EXIF]], [[wikipedia:Extensible_Metadata_Platform][XMP]]
and [[wikipedia:IPTC_Information_Interchange_Model][IPTC]].

There is a significant overhead in loading ExifTool for every command
to be exected. So, exiftool.el starts an ExifTool process in the
[[http://www.sno.phy.queensu.ca/~phil/exiftool/#performance][-stay_open mode]], and passes all commands to it.

* Installation

exiftool.el is available from [[https://melpa.org/][MELPA]]. Or, you can also clone this git
repo and add the path to your /load-path/.

* Functions
  
** High level functions

*** (exiftool-read FILE TAG...)
   
Read TAGS from FILE, return an alist mapping TAGS to values.

If a tag is not found, return an empty string "" as the value. If no
TAGS are specified, read all tags from FILE.

#+BEGIN_SRC emacs-lisp
  (exiftool-read "test1.png" "ImageSize")
  ;; => '(("ImageSize" . "64x64"))
  (exiftool-read "test1.png" "ImageSize" "Interlace")
  ;; => '(("ImageSize" . "64x64") ("Interlace" . "Noninterlaced"))
  (exiftool-read "test1.png")
  ;; => '(("ExifToolVersion" . "10.20")
  ;; ("FileName" . "test1.png")
  ;; ("Directory" . ".")
  ;; ("FileSize" . "1234 bytes")
  ;; ("FileModifyDate" . "2017:02:19 00:31:36+05:30")
  ;; ("FileAccessDate" . "2017:02:22 00:21:53+05:30")
  ;; ("FileInodeChangeDate" . "2017:02:20 00:02:58+05:30")
  ;; ("FilePermissions" . "rw-r--r--")
  ;; ("FileType" . "PNG")
  ;; ("FileTypeExtension" . "png")
  ;; ("MIMEType" . "image/png")
  ;; ("ImageWidth" . "64") ...)
#+END_SRC

*** (exiftool-write FILE (TAG . VALUE)...)
   
Write tags to FILE.

The metadata to be written is specified as (TAG . VALUE) pairs.
Specifying the empty string "" for VALUE deletes that TAG.

#+BEGIN_SRC emacs-lisp
  ;; Set Marked to "True"
  (exiftool-write "test1.png" '("Marked" . "True"))
  ;; Set Marked to "True", and Creator to "Foo"
  (exiftool-write "test1.png"
		     '("Marked" . "True")
		     '("Creator" . "Foo"))
#+END_SRC

*** (exiftool-copy SOURCE DESTINATION &rest TAGS)
   
Copy TAGS from SOURCE file to DESTINATION file.

If no TAGS are specified, copy all tags from SOURCE.

#+BEGIN_SRC emacs-lisp
  ;; Copy all writable tags
  (exiftool-copy "source.png" "destination.png")
  ;; Copy only the tag "Marked"
  (exiftool-copy "source.png" "destination.png" "Marked")
  ;; Copy only the tags "Marked" and "Creator"
  (exiftool-copy "source.png" "destination.png" "Marked" "Creator")
#+END_SRC

** Low level functions
   
*** (exiftool-command &rest ARGS)
   
Execute a command in the currently running exiftool process.

ARGS are arguments of the command to be run, as provided to the
exiftool command line application.

*** (exiftool-run)
   
Start an exiftool process if one is not already running.

If an exiftool process is already running, delete it, and create a new
one.  Return the process object of the newly created process.

* Running tests

Tests are located in the /tests/ folder. You can run them using

#+BEGIN_SRC sh
  make -C tests
#+END_SRC

* Contributing

Feedback, suggestions, feature requests, bug reports and patches are
all welcome. Please contact me by mail at [[mailto:arunisaac@systemreboot.net][arunisaac@systemreboot.net]].

* License

exiftool.el is free software released under the terms of the [[https://www.gnu.org/licenses/gpl.txt][GNU
General Public License]], either version 3 of the License, or (at your
option) any later version.