etags program is used to create a tags table file. It knows
the syntax of several languages, as described in
Here is how to run
etags program reads the specified files, and writes a tags
table named TAGS in the current working directory. You can
intermix compressed and plain text source file names.
knows about the most common compression formats, and does the right
thing. So you can compress all your source files and have
look for compressed versions of its file name arguments, if it does not
find uncompressed versions. 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If the tags table data become outdated due to changes in the files described in the table, the way to update the tags table is the same way it was made in the first place. It is not necessary to do this often.
If the tags table fails to record a tag, or records it for the wrong file, then Emacs cannot possibly find its definition. However, if the position recorded in the tags table becomes a little bit wrong (due to some editing in the file that the tag definition is in), the only consequence is a slight delay in finding the tag. Even if the stored position is very wrong, Emacs will still find the tag, but it must search the entire file for it.
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 effectively 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 contained all the 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
If you specify absolute file names as arguments to
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
etags recognizes tags by regexp matching alone
(see Etags Regexps).
‘etags --help’ prints the list of the languages
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