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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 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 POSIX.1‐2008, 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
created 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 language 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 POSIX.1‐2008, Section 8.2, Internationalization Variables 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 defining 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 escaping <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 <slash> characters 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 POSIX.1‐2008, 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 produce 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
preprocessor 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 historical implementations. The −F option
was omitted as redundant, since it is the default. The −B option was omitted as being of very limited
usefulness. 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 acknowledges 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
(FORTRAN 77) does not (yet) define a similar locale concept. However, a general rule in this volume of
POSIX.1‐2008 is that any time that locales do not match (preparing a file for one locale and processing
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 programs to use the tags in new ways. The format allows either patterns
or line numbers to find the identifiers because the historical vi recognizes 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 trailing <dollar-sign> characters in the search pattern will only
behave correctly 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 languages Pascal and sometimes LISP,
and they understand the C source output 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
POSIX.1‐2008:
−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
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables, Section 12.2, Utility
Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .