Tags Tables =========== A "tags table" is a description of how a multi-file program is broken up into files. It lists the names of the component files and the names and positions of the functions (or other named subunits) in each file. Grouping the related files makes it possible to search or replace through all the files with one command. Recording the function names and positions makes possible the `M-.' command which finds the definition of a function by looking up which of the files it is in. Tags tables are stored in files called "tags table files". The conventional name for a tags table file is `TAGS'. Each entry in the tags table records the name of one tag, the name of the file that the tag is defined in (implicitly), and the position in that file of the tag's definition. Just what names from the described files are recorded in the tags table depends on the programming language of the described file. They normally include all functions and subroutines, and may also include global variables, data types, and anything else convenient. Each name recorded is called a "tag". * Menu: * Tag Syntax:: Tag syntax for various types of code and text files. * Create Tags Table:: Creating a tags table with `etags'. * Select Tags Table:: How to visit a tags table. * Find Tag:: Commands to find the definition of a specific tag. * Tags Search:: Using a tags table for searching and replacing. * List Tags:: Listing and finding tags defined in a file.  File: emacs, Node: Tag Syntax, Next: Create Tags Table, Up: Tags Source File Tag Syntax ---------------------- Here is how tag syntax is defined for the most popular languages: * In C code, any C function or typedef is a tag, and so are definitions of `struct', `union' and `enum'. `#define' macro definitions and `enum' constants are also tags, unless you specify `--no-defines' when making the tags table. Similarly, global variables are tags, unless you specify `--no-globals'. Use of `--no-globals' and `--no-defines' can make the tags table file much smaller. * In C++ code, in addition to all the tag constructs of C code, member functions are also recognized, and optionally member variables if you use the `--members' option. Tags for variables and functions in classes are named `CLASS::VARIABLE' and `CLASS::FUNCTION'. * In Java code, tags include all the constructs recognized in C++, plus the `extends' and `implements' constructs. Tags for variables and functions in classes are named `CLASS.VARIABLE' and `CLASS.FUNCTION'. * In LaTeX text, the argument of any of the commands `\chapter', `\section', `\subsection', `\subsubsection', `\eqno', `\label', `\ref', `\cite', `\bibitem', `\part', `\appendix', `\entry', or `\index', is a tag. Other commands can make tags as well, if you specify them in the environment variable `TEXTAGS' before invoking `etags'. The value of this environment variable should be a colon-separated list of command names. For example, TEXTAGS="def:newcommand:newenvironment" export TEXTAGS specifies (using Bourne shell syntax) that the commands `\def', `\newcommand' and `\newenvironment' also define tags. * In Lisp code, any function defined with `defun', any variable defined with `defvar' or `defconst', and in general the first argument of any expression that starts with `(def' in column zero, is a tag. * In Scheme code, tags include anything defined with `def' or with a construct whose name starts with `def'. They also include variables set with `set!' at top level in the file. Several other languages are also supported: * In assembler code, labels appearing at the beginning of a line, followed by a colon, are tags. * In Bison or Yacc input files, each rule defines as a tag the nonterminal it constructs. The portions of the file that contain C code are parsed as C code. * In Cobol code, tags are paragraph names; that is, any word starting in column 8 and followed by a period. * In Erlang code, the tags are the functions, records, and macros defined in the file. * In Fortran code, functions, subroutines and blockdata are tags. * In Objective C code, tags include Objective C definitions for classes, class categories, methods, and protocols. * In Pascal code, the tags are the functions and procedures defined in the file. * In Perl code, the tags are the procedures defined by the `sub' keyword. * In Postscript code, the tags are the functions. * In Prolog code, a tag name appears at the left margin. You can also generate tags based on regexp matching (*note Create Tags Table::) to handle other formats and languages.  File: emacs, Node: Create Tags Table, Next: Select Tags Table, Prev: Tag Syntax, Up: Tags 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. `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 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. `etags --help' prints the list of the languages `etags' knows, and the file name rules for guessing the language. The `--regex' option provides a general way of recognizing tags based on regexp matching. You can freely intermix it with file names. Each `--regex' option adds to the preceding ones, and applies only to the following files. The syntax is: --regex=/TAGREGEXP[/NAMEREGEXP]/ where TAGREGEXP is used to match the lines to tag. It is always anchored, that is, it behaves as if preceded by `^'. If you want to account for indentation, just match any initial number of blanks by beginning your regular expression with `[ \t]*'. In the regular expressions, `\' quotes the next character, and `\t' stands for the tab character. Note that `etags' does not handle the other C escape sequences for special characters. The syntax of regular expressions in `etags' is the same as in Emacs, augmented with the "interval operator", which works as in `grep' and `ed'. The syntax of an interval operator is `\{M,N\}', and its meaning is to match the preceding expression at least M times and up to N times. You should not match more characters with TAGREGEXP than that needed to recognize what you want to tag. If the match is such that more characters than needed are unavoidably matched by TAGREGEXP, you may find useful to add a NAMEREGEXP, in order to narrow the tag scope. You can find some examples below. The `-R' option deletes all the regexps defined with `--regex' options. It applies to the file names following it, as you can see from the following example: etags --regex=/REG1/ voo.doo --regex=/REG2/ \ bar.ber -R --lang=lisp los.er Here `etags' chooses the parsing language for `voo.doo' and `bar.ber' according to their contents. `etags' also uses REG1 to recognize additional tags in `voo.doo', and both REG1 and REG2 to recognize additional tags in `bar.ber'. `etags' uses the Lisp tags rules, and no regexp matching, to recognize tags in `los.er'. Here are some more examples. The regexps are quoted to protect them from shell interpretation. * Tag the `DEFVAR' macros in the emacs source files: --regex='/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/' * Tag VHDL files (this example is a single long line, broken here for formatting reasons): --language=none --regex='/[ \t]*\(ARCHITECTURE\|CONFIGURATION\) +[^ ]* +OF/' --regex='/[ \t]*\(ATTRIBUTE\|ENTITY\|FUNCTION\|PACKAGE\ \( BODY\)?\|PROCEDURE\|PROCESS\|TYPE\)[ \t]+\([^ \t(]+\)/\3/' * Tag Tcl files (this last example shows the usage of a NAMEREGEXP): --lang=none --regex='/proc[ \t]+\([^ \t]+\)/\1/' For a list of the other available `etags' options, execute `etags --help'.  File: emacs, Node: Select Tags Table, Next: Find Tag, Prev: Create Tags Table, Up: Tags Selecting a Tags Table ---------------------- Emacs has at any time one "selected" tags table, and all the commands for working with tags tables use the selected one. To select a tags table, type `M-x visit-tags-table', which reads the tags table file name as an argument. The name `TAGS' in the default directory is used as the default file name. All this command does is store the file name in the variable `tags-file-name'. Emacs does not actually read in the tags table contents until you try to use them. Setting this variable yourself is just as good as using `visit-tags-table'. The variable's initial value is `nil'; that value tells all the commands for working with tags tables that they must ask for a tags table file name to use. Using `visit-tags-table' when a tags table is already loaded gives you a choice: you can add the new tags table to the current list of tags tables, or start a new list. The tags commands use all the tags tables in the current list. If you start a new list, the new tags table is used _instead_ of others. If you add the new table to the current list, it is used _as well as_ the others. When the tags commands scan the list of tags tables, they don't always start at the beginning of the list; they start with the first tags table (if any) that describes the current file, proceed from there to the end of the list, and then scan from the beginning of the list until they have covered all the tables in the list. You can specify a precise list of tags tables by setting the variable `tags-table-list' to a list of strings, like this: (setq tags-table-list '("~/emacs" "/usr/local/lib/emacs/src")) This tells the tags commands to look at the `TAGS' files in your `~/emacs' directory and in the `/usr/local/lib/emacs/src' directory. The order depends on which file you are in and which tags table mentions that file, as explained above. Do not set both `tags-file-name' and `tags-table-list'.  File: emacs, Node: Find Tag, Next: Tags Search, Prev: Select Tags Table, Up: Tags Finding a Tag ------------- The most important thing that a tags table enables you to do is to find the definition of a specific tag. `M-. TAG ' Find first definition of TAG (`find-tag'). `C-u M-.' Find next alternate definition of last tag specified. `C-u - M-.' Go back to previous tag found. `C-M-. PATTERN ' Find a tag whose name matches PATTERN (`find-tag-regexp'). `C-u C-M-.' Find the next tag whose name matches the last pattern used. `C-x 4 . TAG ' Find first definition of TAG, but display it in another window (`find-tag-other-window'). `C-x 5 . TAG ' Find first definition of TAG, and create a new frame to select the buffer (`find-tag-other-frame'). `M-*' Pop back to where you previously invoked `M-.' and friends. `M-.' (`find-tag') is the command to find the definition of a specified tag. It searches through the tags table for that tag, as a string, and then uses the tags table info to determine the file that the definition is in and the approximate character position in the file of the definition. Then `find-tag' visits that file, moves point to the approximate character position, and searches ever-increasing distances away to find the tag definition. If an empty argument is given (just type ), the sexp in the buffer before or around point is used as the TAG argument. *Note Lists::, for info on sexps. You don't need to give `M-.' the full name of the tag; a part will do. This is because `M-.' finds tags in the table which contain TAG as a substring. However, it prefers an exact match to a substring match. To find other tags that match the same substring, give `find-tag' a numeric argument, as in `C-u M-.'; this does not read a tag name, but continues searching the tags table's text for another tag containing the same substring last used. If you have a real key, `M-0 M-.' is an easier alternative to `C-u M-.'. Like most commands that can switch buffers, `find-tag' has a variant that displays the new buffer in another window, and one that makes a new frame for it. The former is `C-x 4 .', which invokes the command `find-tag-other-window'. The latter is `C-x 5 .', which invokes `find-tag-other-frame'. To move back to places you've found tags recently, use `C-u - M-.'; more generally, `M-.' with a negative numeric argument. This command can take you to another buffer. `C-x 4 .' with a negative argument finds the previous tag location in another window. As well as going back to places you've found tags recently, you can go back to places _from where_ you found them. Use `M-*', which invokes the command `pop-tag-mark', for this. Typically you would find and study the definition of something with `M-.' and then return to where you were with `M-*'. Both `C-u - M-.' and `M-*' allow you to retrace your steps to a depth determined by the variable `find-tag-marker-ring-length'. The command `C-M-.' (`find-tag-regexp') visits the tags that match a specified regular expression. It is just like `M-.' except that it does regexp matching instead of substring matching.  File: emacs, Node: Tags Search, Next: List Tags, Prev: Find Tag, Up: Tags Searching and Replacing with Tags Tables ---------------------------------------- The commands in this section visit and search all the files listed in the selected tags table, one by one. For these commands, the tags table serves only to specify a sequence of files to search. `M-x tags-search REGEXP ' Search for REGEXP through the files in the selected tags table. `M-x tags-query-replace REGEXP REPLACEMENT ' Perform a `query-replace-regexp' on each file in the selected tags table. `M-,' Restart one of the commands above, from the current location of point (`tags-loop-continue'). `M-x tags-search' reads a regexp using the minibuffer, then searches for matches in all the files in the selected tags table, one file at a time. It displays the name of the file being searched so you can follow its progress. As soon as it finds an occurrence, `tags-search' returns. Having found one match, you probably want to find all the rest. To find one more match, type `M-,' (`tags-loop-continue') to resume the `tags-search'. This searches the rest of the current buffer, followed by the remaining files of the tags table. `M-x tags-query-replace' performs a single `query-replace-regexp' through all the files in the tags table. It reads a regexp to search for and a string to replace with, just like ordinary `M-x query-replace-regexp'. It searches much like `M-x tags-search', but repeatedly, processing matches according to your input. *Note Replace::, for more information on query replace. It is possible to get through all the files in the tags table with a single invocation of `M-x tags-query-replace'. But often it is useful to exit temporarily, which you can do with any input event that has no special query replace meaning. You can resume the query replace subsequently by typing `M-,'; this command resumes the last tags search or replace command that you did. The commands in this section carry out much broader searches than the `find-tag' family. The `find-tag' commands search only for definitions of tags that match your substring or regexp. The commands `tags-search' and `tags-query-replace' find every occurrence of the regexp, as ordinary search commands and replace commands do in the current buffer. These commands create buffers only temporarily for the files that they have to search (those which are not already visited in Emacs buffers). Buffers in which no match is found are quickly killed; the others continue to exist. It may have struck you that `tags-search' is a lot like `grep'. You can also run `grep' itself as an inferior of Emacs and have Emacs show you the matching lines one by one. This works much like running a compilation; finding the source locations of the `grep' matches works like finding the compilation errors. *Note Compilation::.  File: emacs, Node: List Tags, Prev: Tags Search, Up: Tags Tags Table Inquiries -------------------- `M-x list-tags FILE ' Display a list of the tags defined in the program file FILE. `M-x tags-apropos REGEXP ' Display a list of all tags matching REGEXP. `M-x list-tags' reads the name of one of the files described by the selected tags table, and displays a list of all the tags defined in that file. The "file name" argument is really just a string to compare against the file names recorded in the tags table; it is read as a string rather than as a file name. Therefore, completion and defaulting are not available, and you must enter the file name the same way it appears in the tags table. Do not include a directory as part of the file name unless the file name recorded in the tags table includes a directory. `M-x tags-apropos' is like `apropos' for tags (*note Apropos::). It reads a regexp, then finds all the tags in the selected tags table whose entries match that regexp, and displays the tag names found. You can also perform completion in the buffer on the name space of tag names in the current tags tables. *Note Symbol Completion::.