Ctags

Last updated
Ctags (BSD)
Developer(s) Ken Arnold
Repository
Operating system Unix and Unix-like
Platform Cross-platform
Type Programming tool (Specifically: Code navigation tool)
License BSD

ctags is a shell command that generates an index (tag) file of programmatic identifiers parsed from source code files of various programming languages to aid with code comprehension. The tags are often used by a source-code editor to lookup the definition of an identifier while the user develops the source code. Alternatively, the command supports an output format that is a human-readable cross reference.

Contents

The original ctags was introduced in BSD Unix 2.0 [1] [2] and was written by Ken Arnold, with Fortran support by Jim Kleckner and Pascal support by Bill Joy. It is part of the initial release of Single Unix Specification and XPG4 of 1992.

Editor support

Tag index files are supported by many editors, including:

Variants

Original

The original ctags command is generally not supported today but its functionality is still commonly available today via programs that are similar and possibly compatible. In particular, the original tag data format is still commonly used.

The original format, often used with vi and its clones as well as by the modern descendent programs Exuberant and Universal Ctags. [6] A tags file, normally named "tags", consists of lines formatted as:

{tagname}\t{tagfile}\t{tagaddress}

The fields are:

The lines are sorted on {tagname} which allows for fast searching.

Extended Ctags

The format used by Vim's Exuberant Ctags and Universal Ctags. These programs can generate an original ctags file format or an extended format that attempts to retain backward compatibility.

A file consists of lines formatted as:

{tagname}\t{tagfile}\t{tagaddress}[;"\t{tagfield...}]

The fields up to and including {tagaddress} are the same as for the original ctags format. Optional, additional fields (indicated by square brackets) include:

This format is compatible with non-POSIX vi as the additional data is interpreted as a comment. POSIX implementations of vi must be changed to support it, however. [6]

etags

GNU Emacs comes with two ctags variants, etags and ctags, which are built from the same source code. etags generates a tag table file for Emacs, and ctags creates a tags file for vi. Some options (e.g. --language) are accepted by both ctags and etags. Options which only make sense when generating a vi-style tags file are not accepted (and are therefore reported as errors) by etags. Similarly ctags does not accept options which are pertinent only to generating a tag table file for Emacs. [7]

For Emacs, the tags file is normally named "TAGS". The file consists of multiple sections – one section per input source file. Sections are plain-text with several non-printable ASCII characters used for special purposes. These characters are represented as underlined hexadecimal codes below.

A section starts with a two line header (the first two bytes make up a magic number):

\x0c {src_file},{size_of_tag_definition_data_in_bytes}

Note, \x## represents the byte in hexadecimal ##. Every line ends with a line feed (LF, \n = \x0A).

The header is followed by tag definitions, one definition per line, with the format:

{tag_definition_text}\x7f{tagname}\x01{line_number},{byte_offset}

{tagname}\x01 can be omitted if the name of the tag can be deduced from the text at the tag definition.

Exuberant Ctags

Exuberant Ctags, written and maintained by Darren Hiebert until 2009, [8] was initially distributed with Vim, but became a separate project upon the release of Vim 6. It includes support for Emacs and etags compatibility. [9] [10]

Exuberant Ctags includes support for over 40 programming languages with the ability to add support for even more using regular expressions.

Universal Ctags

Universal Ctags is a fork of Exuberant Ctags, with the objective of continuing its development. A few parsers are rewritten to better support the languages. [11]

Hasktags

Creates a ctags-compatible tag file for Haskell source files. [12] It includes support for creating Emacs etags files. [13]

jsctags

A ctags-compatible solution specialized for JavaScript using the CommonJS packaging system. [14] It outperforms Exuberant Ctags for JavaScript code, finding more tags than the latter. [15]

Example

Given a single line test.c source code:

#define CCC(x)

The ctags tag file looks like:

CCC( test.c 1

The etags tag file (TAGS) looks like this:

\x0c test.c,21 #define CCC(\x7fCCC\x011,0

See also

References

  1. ↑ "2BSD/man/ctags.u". www.tuhs.org. Retrieved 2024-10-21.
  2. ↑ "2BSD/src/ctags.sh". www.tuhs.org. Retrieved 2024-10-21.
  3. ↑ "Language Server Protocol". CodeLite Documentation. Retrieved 2022-06-12.
  4. ↑ "Aminet - dev/C/Ctags.lha".
  5. ↑ Workspace Symbols, Python for Visual Studio Code Docs
  6. 1 2 "Proposal for extended Vi tags file format" . Retrieved 2007-06-30.
  7. ↑ etags.emacs(1)  –  Linux General Commands Manual
  8. ↑ "Exuberant Ctags". ctags.sourceforge.net.
  9. ↑ "Vim documentation: version6: ctags-gone" . Retrieved 2007-04-28.
  10. ↑ etags.ctags(1)  –  Linux General Commands Manual
  11. ↑ "Universal Ctags Documentation" . Retrieved 2018-08-02.
  12. ↑ "GHC documentation: Other Haskell utility programs" . Retrieved 2010-03-05.
  13. ↑ "hasktags: Produces ctags "tags" and etags "TAGS" files for Haskell programs" . Retrieved 2010-03-05.
  14. ↑ "pcwalton github repository for jsctags". GitHub . Archived from the original on 2010-08-22. Retrieved 2016-09-10.
  15. ↑ Patrick Walton (25 May 2010). "Introducing jsctags" . Retrieved 2010-05-25.
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