CTAGS(1P) POSIX Programmer's Manual CTAGS(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
ctags - create a tags file (DEVELOPMENT, FORTRAN)
SYNOPSIS
ctags [-a][-f tagsfile] pathname ...
ctags -x pathname ...
DESCRIPTION
The ctags utility shall be provided on systems that support the User
Portability Utilities option, the Software Development Utilities
option, and either or both of the C-Language Development Utilities
option and FORTRAN Development Utilities option. On other systems, it
is optional.
The ctags utility shall write a tagsfile or an index of objects from C-
language or FORTRAN source files specified by the pathname operands.
The tagsfile shall list the locators of language-specific objects
within the source files. A locator consists of a name, pathname, and
either a search pattern or a line number that can be used in searching
for the object definition. The objects that shall be recognized are
specified in the EXTENDED DESCRIPTION section.
OPTIONS
The ctags utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-a Append to tagsfile.
-f tagsfile
Write the object locator lists into tagsfile instead of the
default file named tags in the current directory.
-x Produce a list of object names, the line number, and filename in
which each is defined, as well as the text of that line, and
write this to the standard output. A tagsfile shall not be cre-
ated when -x is specified.
OPERANDS
The following pathname operands are supported:
file.c Files with basenames ending with the .c suffix shall be treated
as C-language source code. Such files that are not valid input
to c99 produce unspecified results.
file.h Files with basenames ending with the .h suffix shall be treated
as C-language source code. Such files that are not valid input
to c99 produce unspecified results.
file.f Files with basenames ending with the .f suffix shall be treated
as FORTRAN-language source code. Such files that are not valid
input to fort77 produce unspecified results.
The handling of other files is implementation-defined.
STDIN
See the INPUT FILES section.
INPUT FILES
The input files shall be text files containing source code in the lan-
guage indicated by the operand filename suffixes.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
ctags:
LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari-
ables for the precedence of internationalization variables used
to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.
LC_COLLATE
Determine the order in which output is sorted for the -x option.
The POSIX locale determines the order in which the tagsfile is
written.
LC_CTYPE
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files).
When processing C-language source code, if the locale is not
compatible with the C locale described by the ISO C standard,
the results are unspecified.
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of
LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
The list of object name information produced by the -x option shall be
written to standard output in the following format:
"%s %d %s %s", <object-name>, <line-number>, <filename>, <text>
where <text> is the text of line <line-number> of file <filename>.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
When the -x option is not specified, the format of the output file
shall be:
"%s\t%s\t/%s/\n", <identifier>, <filename>, <pattern>
where <pattern> is a search pattern that could be used by an editor to
find the defining instance of <identifier> in <filename> (where defin-
ing instance is indicated by the declarations listed in the EXTENDED
DESCRIPTION).
An optional circumflex ( '^' ) can be added as a prefix to <pattern>,
and an optional dollar sign can be appended to <pattern> to indicate
that the pattern is anchored to the beginning (end) of a line of text.
Any slash or backslash characters in <pattern> shall be preceded by a
backslash character. The anchoring circumflex, dollar sign, and escap-
ing backslash characters shall not be considered part of the search
pattern. All other characters in the search pattern shall be considered
literal characters.
An alternative format is:
"%s\t%s\t?%s?\n", <identifier>, <filename>, <pattern>
which is identical to the first format except that slashes in <pattern>
shall not be preceded by escaping backslash characters, and question
mark characters in <pattern> shall be preceded by backslash characters.
A second alternative format is:
"%s\t%s\t%d\n", <identifier>, <filename>, <lineno>
where <lineno> is a decimal line number that could be used by an editor
to find <identifier> in <filename>.
Neither alternative format shall be produced by ctags when it is used
as described by IEEE Std 1003.1-2001, but the standard utilities that
process tags files shall be able to process those formats as well as
the first format.
In any of these formats, the file shall be sorted by identifier, based
on the collation sequence in the POSIX locale.
EXTENDED DESCRIPTION
If the operand identifies C-language source, the ctags utility shall
attempt to produce an output line for each of the following objects:
* Function definitions
* Type definitions
* Macros with arguments
It may also produce output for any of the following objects:
* Function prototypes
* Structures
* Unions
* Global variable definitions
* Enumeration types
* Macros without arguments
* #define statements
* #line statements
Any #if and #ifdef statements shall produce no output. The tag main is
treated specially in C programs. The tag formed shall be created by
prefixing M to the name of the file, with the trailing .c, and leading
pathname components (if any) removed.
On systems that do not support the C-Language Development Utilities
option, ctags produces unspecified results for C-language source code
files. It should write to standard error a message identifying this
condition and cause a non-zero exit status to be produced.
If the operand identifies FORTRAN source, the ctags utility shall pro-
duce an output line for each function definition. It may also produce
output for any of the following objects:
* Subroutine definitions
* COMMON statements
* PARAMETER statements
* DATA and BLOCK DATA statements
* Statement numbers
On systems that do not support the FORTRAN Development Utilities
option, ctags produces unspecified results for FORTRAN source code
files. It should write to standard error a message identifying this
condition and cause a non-zero exit status to be produced.
It is implementation-defined what other objects (including duplicate
identifiers) produce output.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The output with -x is meant to be a simple index that can be written
out as an off-line readable function index. If the input files to ctags
(such as .c files) were not created using the same locale as that in
effect when ctags -x is run, results might not be as expected.
The description of C-language processing says "attempts to" because the
C language can be greatly confused, especially through the use of
#defines, and this utility would be of no use if the real C preproces-
sor were run to identify them. The output from ctags may be fooled and
incorrect for various constructs.
EXAMPLES
None.
RATIONALE
The option list was significantly reduced from that provided by histor-
ical implementations. The -F option was omitted as redundant, since it
is the default. The -B option was omitted as being of very limited use-
fulness. The -t option was omitted since the recognition of typedefs is
now required for C source files. The -u option was omitted because the
update function was judged to be not only inefficient, but also rarely
needed.
An early proposal included a -w option to suppress warning diagnostics.
Since the types of such diagnostics could not be described, the option
was omitted as being not useful.
The text for LC_CTYPE about compatibility with the C locale acknowl-
edges that the ISO C standard imposes requirements on the locale used
to process C source. This could easily be a superset of that known as
"the C locale" by way of implementation extensions, or one of a few
alternative locales for systems supporting different codesets. No
statement is made for FORTRAN because the ANSI X3.9-1978 standard (FOR-
TRAN 77) does not (yet) define a similar locale concept. However, a
general rule in this volume of IEEE Std 1003.1-2001 is that any time
that locales do not match (preparing a file for one locale and process-
ing it in another), the results are suspect.
The collation sequence of the tags file is not affected by LC_COLLATE
because it is typically not used by human readers, but only by programs
such as vi to locate the tag within the source files. Using the POSIX
locale eliminates some of the problems of coordinating locales between
the ctags file creator and the vi file reader.
Historically, the tags file has been used only by ex and vi. However,
the format of the tags file has been published to encourage other pro-
grams to use the tags in new ways. The format allows either patterns or
line numbers to find the identifiers because the historical vi recog-
nizes either. The ctags utility does not produce the format using line
numbers because it is not useful following any source file changes that
add or delete lines. The documented search patterns match historical
practice. It should be noted that literal leading circumflex or trail-
ing dollar-sign characters in the search pattern will only behave cor-
rectly if anchored to the beginning of the line or end of the line by
an additional circumflex or dollar-sign character.
Historical implementations also understand the objects used by the lan-
guages Pascal and sometimes LISP, and they understand the C source out-
put by lex and yacc. The ctags utility is not required to accommodate
these languages, although implementors are encouraged to do so.
The following historical option was not specified, as vgrind is not
included in this volume of IEEE Std 1003.1-2001:
-v If the -v flag is given, an index of the form expected by vgrind
is produced on the standard output. This listing contains the
function name, filename, and page number (assuming 64-line
pages). Since the output is sorted into lexicographic order, it
may be desired to run the output through sort -f. Sample use:
ctags -v files | sort -f > index vgrind -x index
The special treatment of the tag main makes the use of ctags practical
in directories with more than one program.
FUTURE DIRECTIONS
None.
SEE ALSO
c99, fort77, vi
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 CTAGS(1P)
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