Combining strings and tag values

[Bona Sierra]

Hi,
I want to combine the filename and a string as a new tag value, e.g.

exiftool -P -overwrite_original -UserComment="some text" "-UserComment+<<${filename;s/\.[^.]*$//}" FILES

The result is:
Warning: No writable tags set from FILES

The problems seems to be the "-UserComment+<<${filename;s/\.[^.]*$//}", but I have no idea how it can work.

[StarGeek]

You can't both assign a value and copy a tag value separately to the same tag in one command. From note #1 under the -TAG[+-^]=[VALUE] option

Many tag values may be assigned in a single command. If two assignments affect the same tag, the latter takes precedence

So in your command, -UserComment="some text" would be ignored.

The correct command would be found under the -TagsFromFile option

An extension of the redirection feature allows strings involving tag names to be used on the right hand side of the < symbol with the syntax "'-DSTTAG<STR'", where tag names in STR are prefixed with a $ symbol.

Also, you can use the BaseName tag instead of the Filename to remove the extension

Here's an example using multiple static texts and multiple tags
exiftool -P -overwrite_original "-UserComment<some text $Basename some more text $Model" /path/to/files/

[Bona Sierra]

Hi StarGeek,

thank you for this advice, I will report my results later today after todays european championships soccer games.

And sorry for the "<<" typo. I hope it didn't cause any confusion. 

Btw: I thought it should be possible to add another string to a tag within one command line using the '+=' or '+<' operator.

Bona

[StarGeek]

Btw: I thought it should be possible to add another string to a tag within one command line using the '+=' or '+<' operator.

These can only be used in a few situations

• Add/remove from a list type tag
• Shift a Date/Time tag
• Shift a simple number tag
• Conditionally remove a value

For +=, from the docs on the -TAG[+-^]=[VALUE] option

+= and -= are used to add or remove existing entries from a list, or to shift date/time values (see Image::ExifTool::Shift.pl and note 6 below for more details). += may also be used to increment numerical values (or decrement if VALUE is negative), and -= may be used to conditionally delete or replace a tag (see "WRITING EXAMPLES" for examples).

For +<, from the docs on the -TagsFromFile option

+<= or -<= may also be used to add or delete specific list entries, or to shift date/time values.

[Bona Sierra]

thanks for the explanation.

Now I understood, this means none of the JPEG and EXIF tags, but some of the IPTC and many of XMP tags which are list type tags, as indicated by the '+' sign in the tag names list.

good to know