etags - Unix, Linux Command

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NAME

etags, ctags - generate tag file for Emacs, vi

SYNOPSIS

etags [-aCDGImRVh] [-i file] [-l language] [-o tagfile] [-r regexp]
[--append] [--no-defines] [--no-globals] [--include=file] [--ignore-indentation] [--language=language] [--members] [--output=tagfile] [--regex=regexp] [--no-regex] [--ignore-case-regex=regexp] [--help] [--version] file ...

ctags [-aCdgImRVh] [-BtTuvwx] [-l language] [-o tagfile] [-r regexp]
[--append] [--backward-search] [--cxref] [--defines] [--forward-search] [--globals] [--ignore-indentation] [--language=language] [--members] [--output=tagfile] [--regex=regexp] [--ignore-case-regex=regexp] [--typedefs] [--typedefs-and-c++] [--update] [--no-warn] [--help] [--version] file ...

DESCRIPTION

The etags program is used to create a tag table file, in a format understood by emacs(1) ; the ctags program is used to create a similar table in a format understood by vi(1) . Both forms of the program understand the syntax of C, Objective C, C++, Java, Fortran, Ada, Cobol, Erlang, LaTeX, Emacs Lisp/Common Lisp, makefiles, Pascal, Perl, Postscript, Python, Prolog, Scheme and most assembler-like syntaxes. Both forms read the files specified on the command line, and write a tag table (defaults: TAGS for etags, tags for ctags) in the current working directory. Files specified with relative file names will be recorded in the tag table with file names relative to the directory where the tag table resides. Files specified with absolute file names will be recorded with absolute file names. The programs recognize the language used in an input file based on its file name and contents. The --language switch can be used to force parsing of the file names following the switch according to the given language, overriding guesses based on filename extensions.

OPTIONS

Some options make sense only for the vi style tag files produced by ctags; etags does not recognize them. The programs accept unambiguous abbreviations for long option names.

EXAMPLES

Navigating the source code using vi or emacs editor could be quite a task especially if the code has multiple files. gctags utility can be quite handy in such a situation. Using gctags vi can be converted into a beautiful source code browser.

Example given below is for C program but same can be applied for other languages like C++, java, Perl, etc. Type gctags --h for to see supported languages.

Consider below source code: gctags_example.c

#include <stdio.h>
// Function Declarations
int areaRectangle(int length, int breadth);
float areaCircle(int radius);
int square(int num);
void dummy();
#define PI 3.14
typedef struct {
        int memberInt;
        float memberFloat;
        char memberChar;
} myStruct;
int rectangle;
float circle;
int areaRectangle(int length, int breadth)
{
        return(length * breadth);
}
float areaCircle(int radius)
{
        return(PI * square(radius));
}
int square(int num)
{
        return(num * num);
}
int main()
{
        rectangle = areaRectangle(10, 5);
        circle = areaCircle(20);
        printf("Area of rectangle: %f", rectangle);
        printf("Area of circle: %f", circle);
        return(0);
}

Step 1: Create a tags file

$ gctags --declarations --defines --global --members --output=example.tags --no-warn gctags_example.c

Above command will create the tags file example.tags. Without the --output option the file name would be tags

$ ls
example.tags  gctags_example.c

Below are the contents of example.tags:

$ cat example.tags
Mgctags_example gctags_example.c        /^int main()$/
PI      gctags_example.c        9
areaCircle      gctags_example.c        /^float areaCircle(int radius);$/
areaRectangle   gctags_example.c        /^int areaRectangle(int length, int breadth);$/
circle  gctags_example.c        18
dummy   gctags_example.c        /^void dummy();$/
memberChar      gctags_example.c        14
memberFloat     gctags_example.c        13
memberInt       gctags_example.c        12
myStruct        gctags_example.c        15
rectangle       gctags_example.c        17
square  gctags_example.c        /^int square(int num);$/

Based on the options given, tags have been created for various parts of the code. Example, option --global creates tags for global variables and due to option --defines creates tags for #define and so on. Above command has been used for single file. But with slight modification the same command can work for multiple files and also search directories recursively.

Below command creates tags for all .c and .h files. -R option is used to search directories recursively under current directory.

$ gctags -R --declarations --defines --global --members --output=example.tags --no-warn *.c *.hae

Step 2: Set the path for tags file
This is required if you have specified custom tags file and not using the default file "tags".

Open the an source file in vi editor and give below command.

:set tags=<path to tags>

Step 3: With the tags path set, you are now ready to browse source code

Below table shows the commands that can be used to navigate the source in vi editor