copy FileModifyDateTime to OrignalDateTime

[DavidB42]

New to this an just beyond testing some of the given examples to better understand syntax.

But what I really want to do right now is  copy  (into the) OriginalDateTIme tab from the FileModifyDateTime tab if the OriginalDateTime is missing, recursively for the specified directorytree.

After some hair pulling, I tried
exiftool -DateTimeOriginal<filemodifydate -if "not DateTimeOriginal" dir

only to get
The system cannot find the file specified.

which didn't help me  much.

Appreciate the help thanks.

(I am in wonder over the ExifTool right now;  but baffled too.)

[StarGeek]

You're close, but there are two errors.

First, you need quotes around the tag copy.  From the fourth paragraph under the -TagsFromFile option
   Note that this argument must be quoted to prevent shell redirection
Shell redirection is a property of the command line (CMD on Windows, Bash on Linux, Terminal on Mac) where either the output and/or the input of the command is written to or read from a file.  Without quotes, the -DateTimeOriginal<filemodifydate tells the computer to try and read from  a file named filemodifydate.

The second problem is the -if statement.  From the docs on the -if option:
   EXPR is a Perl-like logic expression containing tag names prefixed by $ symbols.
So you need a $ in front of DateTimeOriginal.

Putting it all together
exiftool  "-DateTimeOriginal<filemodifydate" -if "not $DateTimeOriginal" dir

If you're not on Windows, then change the double quotes to single quotes.  Don't copy/paste this into a Word Processor/Google docs because those will change the "normal quotes" into "fancy quotes" which do not work.

[DavidB42]

Thank you
appreciate the thoroughness of your response and the quick response.
Works as advertised