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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.1‐2017, 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.1‐2017, 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.1‐2017 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.1‐2017:
-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.1‐2017, 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
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
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 .