scribbu

The scribbu project has a few components. The first is a program that provides assorted sub-commands, a few of which are:

scribbu dump will write the contents of any & all ID3 tags found in one or more files to stdout. See Invoking scribbu dump.
scribbu report will generate a report listing ID3 attributes on one or more files on stdout. CSV, TDF & ASCII-delimited formats are supported currently. See Invoking scribbu report.
scribbu rename will rename one or more files based on the contents of their ID3 tags; e.g. scribbu rename -t ``%A-%T.mp3'' *.mp3 will rename all the files matching “*.mp3” to “<artist>-<title>.mp3” where "artist" and "title" are derived from their ID3 tags (if any). See Invoking scribbu rename.
scribbu popm will update ID3v2 play count & popularimeter tags. For instance, scribbu popm foo.mp3 will increment the play counts in “foo.mp3”. See Invoking scribbu popm.
scribbu text maintains assorted ID3v2 text frames; for instance, scribbu text --artist='Roxy Music' *.mp3 will set the artist frame to “Roxy Music” in all ID3v2 tags in all files matching “*.mp3”. See Invoking scribbu text.

Any sub-command can be invoked with --help or -h for more information. Use --info option to display the command’s node in this manual.

The scribbu program also exports functions & GOOPS (see GOOPS) classes to a Scheme interpreter, so scribbu can also be invoked...

with a Scheme expression (-e, --expression) or Scheme file (-f, --file). In this case, scribbu will evaluate the given program & exit.
with no arguments at all. In this case, scribbu will drop into a Scheme REPL (Read Evaluate Print Loop) in which the user can evaluate arbitrary Scheme expressions.

as a script:

#!/usr/local/scribbu \
-e main -s
#!
(define (main args)
    ...

Finally, scribbu contains a C++ library (libscribbu, see Using libscribbu) against which one can build C++ libraries & programs.