GNU Info

(emacs)Create Tags Table

---

Next: Etags Regexps Prev: Tag Syntax Up: Tags

---

Enter node , (file) or (file)node

Creating Tags Tables
--------------------

   The `etags' program is used to create a tags table file.  It knows
the syntax of several languages, as described in Note: Tag Syntax.
Here is how to run `etags':

     etags INPUTFILES...

The `etags' program reads the specified files, and writes a tags table
named `TAGS' in the current working directory.

   If the specified files don't exist, `etags' looks for compressed
versions of them and uncompresses them to read them.  Under MS-DOS,
`etags' also looks for file names like `mycode.cgz' if it is given
`mycode.c' on the command line and `mycode.c' does not exist.

   `etags' recognizes the language used in an input file based on its
file name and contents.  You can specify the language with the
`--language=NAME' option, described below.

   If the tags table data become outdated due to changes in the files
described in the table, the way to update the tags table is the same
way it was made in the first place.  If the tags table fails to record
a tag, or records it for the wrong file, then Emacs cannot possibly
find its definition until you update the tags table.  However, if the
position recorded in the tags table becomes a little bit wrong (due to
other editing), the only consequence is a slight delay in finding the
tag.  Even if the stored position is very far wrong, Emacs will still
find the tag, after searching most of the file for it.  Even that delay
is hardly noticeable with today's computers.

   So you should update a tags table when you define new tags that you
want to have listed, or when you move tag definitions from one file to
another, or when changes become substantial.  Normally there is no need
to update the tags table after each edit, or even every day.

   One tags table can virtually include another.  Specify the included
tags file name with the `--include=FILE' option when creating the file
that is to include it.  The latter file then acts as if it covered all
the source files specified in the included file, as well as the files
it directly contains.

   If you specify the source files with relative file names when you run
`etags', the tags file will contain file names relative to the
directory where the tags file was initially written.  This way, you can
move an entire directory tree containing both the tags file and the
source files, and the tags file will still refer correctly to the source
files.

   If you specify absolute file names as arguments to `etags', then the
tags file will contain absolute file names.  This way, the tags file
will still refer to the same files even if you move it, as long as the
source files remain in the same place.  Absolute file names start with
`/', or with `DEVICE:/' on MS-DOS and MS-Windows.

   When you want to make a tags table from a great number of files, you
may have problems listing them on the command line, because some systems
have a limit on its length.  The simplest way to circumvent this limit
is to tell `etags' to read the file names from its standard input, by
typing a dash in place of the file names, like this:

     find . -name "*.[chCH]" -print | etags -

   Use the option `--language=NAME' to specify the language explicitly.
You can intermix these options with file names; each one applies to
the file names that follow it.  Specify `--language=auto' to tell
`etags' to resume guessing the language from the file names and file
contents.  Specify `--language=none' to turn off language-specific
processing entirely; then `etags' recognizes tags by regexp matching
alone (Note: Etags Regexps).

   `etags --help' prints the list of the languages `etags' knows, and
the file name rules for guessing the language.  It also prints a list
of all the available `etags' options, together with a short explanation.