extract(1) - determine meta-information about a file
-a      Do not remove any duplicates, even if the keywords match exactly and have  the  same  type  (i.e.
        because the same keyword was found by different extractor libraries).
-b      Display the output in BiBTeX format. This implies the -d option
-B LANG Use  the  generic  plaintext  extractor  for  the  language with the 2-letter language code LANG.
        Supported languages are DA (Danish), DE (German), EN (English), ES (Spanish),  FI  (Finnish),  FR
        (French), GA (Gaelic), IT (Italian), NO (Norwegian) and SV (Swedish).
-d      Remove  duplicates  only  if  the  types match exactly. By default, duplicates are removed if the
        types match or if one of the types is I unknown (in this case, the duplicate of unknown  type  is
-f      add the filename(s) (without directory) to the list of keywords.
-g      Use  grep-friendly  output (all keywords on a single line for each file).  Use the verbose option
        to print the filename first, followed by the keywords.  Use the  verbose  option  twice  to  also
        display the keyword types.  This option will not print keyword types or non-textual metadata.
-h      Print a brief summary of the options.
        Use the ALGORITHM to compute a hash of each file (possible algorithms are sha1 and md5).
-L      Print a list of all known keyword types.
-n      Do  not use the default set of extractors (typically all standard extractors, currently mp3, ogg,
        jpg, gif, png, tiff, real, html, pdf and mime-types), use only the extractors specified with  the
        .B -l option.
-r      Remove all duplicates disregarding differences in the keyword type.
-s      Split  keywords  at  delimiters  (space,  comma, colon, etc.) and list split keywords to be of .I
        unknown type. This can also be done by loading the split-library. Using  this  option  guarantees
        that  the  splitting is performed after all other libraries have been run. It is always performed
        before duplicate elimination.
-v      Print the version number and exit.

-V      Be verbose.
-B      Run the printable extractor (costly, generic extractor for binaries)
-l libraries
        Use the specified  libraries  to  extract  keywords.  The  general  format  of  libraries  is  .I
        [[-]LIBRARYNAME[:[-]LIBRARYNAME]*]  where  LIBRARYNAME  is  a libextractor compatible library and
        typically of the form .I libextractor_jpeg.so. The minus before the  libraryname  indicates  that
        this  library  should  be run after all the libraries that were specified so far. If the minus is
        missing, the library is run before all previously specified libraries.

-p type Print only the keywords matching the specified type. By default, all keywords that are found  and
        not removed as duplicates are printed.
-x type Exclude  keywords  of the specified type from the output. By default, all keywords that are found
        and not removed as duplicates are printed.