Requires python3 and eyed3. Modeled off of the tag editor in Predixis Music Magic Mixer. That being the source to destination pattern matching thing.

usage: pytag [-h] [-d] [-f] [-r] [-o] [-l] [-e [myeditor]]
             [source] [dest] [file [file ...]]

Usage:
    pytag file...
    pytag source dest file...
    pytag -f dest file...
    pytag dest file...

    In the first usage just list the tags of file(s). Equivalent to -l.

    In the second and third usage set the tags specified in dest from
    the string specified in source. Passing -f is equivalent to passing
    source as "{filename}".

    In the fourth usage print the string specified in dest with
    substitutions applied.

    The source argument is used to provide a string that dest matches
    against to extract tags from. It can use the python curly-brace
    format string syntax to substitute values into the string.
    Eg "{p1}::{album}::{filename}".
    Valid keys are lower case ID3 tags, when present in the file, along
    with a few extra ones:
        filename  The basename of the file.
        ext       The file extension.
        pdir      The dirname of the absolute path to the file.
        p1        The parent directory of the file.
        p2..N     The Nth parent directory of the file.
    Use the -l argument to see all available ones for a file (except for
    the pN key which are dynamiccaly generated).

    The dest argument is used to set tags from match expressions or to
    rename the file to the specified string (with the same keys available
    as specified for source). Additionally to what was described above
    for source you can suffix a keyname with an asterix to specify a
    greedy match (eg "{track*}"). You can also, with the -r flag, pass a
    valid python regex. It can still have curly-brace delimited keys in
    it and name match groups are matched to tags to set.

    There are is is one other transform available in dest right now eg
    "{track^}" (or {track*^} if you want it greedy) will turn all
    underscores to spaces and sentence case tag. Eg.

        like_a_stone_(live)_(bonus_track) => Like a Stone (Live) (Bonus Track)

Examples:

    # Set tags from filename
    pytag -f "{track}. {artist} - {title}.mp3" file

    # Set tags from parent dir, fixed strings and filename
    pytag "{p1}::Big Joe::2013::{filename}" "{album}::{artist}::{year}::{track} {title}_junk.mp3" file

    # Rename file(s) from tags.
    pytag "{track:02} - {artist} - {title}.{ext}" "{filename}" file

positional arguments:
  source
  dest
  file                  The file(s) to operate on.

optional arguments:
  -h, --help            show this help message and exit
  -d, --dry-run         Print what would be done, but don't do it.
  -f                    Use filename as source. Equivalent to passing
                        "{filename}" as the first positional argument.
  -r, --regex           The dest string is a (python) regex. Don't escape it.
  -o, --stdout          Print the transformed source string to stdout. Don't
                        perform the operation. When renaming a file just print
                        out the new filename. When setting tags print out the
                        changed tags in rfc822(-ish) format.
  -l, --list            Just print the tags from the file (plus a couple
                        extra) in rfc822 format.
  -e [myeditor], --editor [myeditor]
                        Open (expanded) dest string(s) an editor before
                        applying to dest. Default if no source is specified is
                        dest. Default for source and dest if neither are
                        specified is
                        {filename}::{album}::{track}::{artist}::{title}. You
                        can specify arguments to the external program (like
                        sed) with shell quoting. Prefixing the command name
                        with '-' will use stdin and stdout otherwise a file to
                        operate on will be passed as the final argument.