readtags - Find tag file entries matching specified names
readtags -h | --help readtags (-H | --help-expression) (filter|sorter) readtags [OPTION]... ACTION
The readtags program filters, sorts and prints tag entries in a tags file. The basic filtering is done using actions, by which you can list all regular tags, pseudo tags or regular tags matching specific name. Then, further filtering and sorting can be done using post processors, namely filter expressions and sorter expressions.
Controlling the Tags Reading Behavior¶
The behavior of reading tags can be controlled using these options:
The NAME action will perform binary search on sorted (including "foldcase") tags files, which is much faster then on unsorted tags files.
Controlling the NAME Action Behavior¶
The behavior of the NAME action can be controlled using these options:
Controlling the Output¶
By default, the output of readtags contains only the name, input and pattern field. The Output can be tweaked using these options:
About the -E option: certain characters are escaped in a tags file, to make it machine-readable. e.g., ensuring no tabs character appear in fields other than the pattern field. By default, readtags translates them to make it human-readable, but when utilizing readtags output in a script or a client tool, -E option should be used. See ctags-client-tools(7) for more discussion on this.
Filtering and Sorting¶
Further filtering and sorting on the tags listed by actions are performed using:
These are discussed in the EXPRESSION section.
- List all tags in "/path/to/tags":
$ readtags -t /path/to/tags -l
- List all tags in "tags" that start with "mymethod":
$ readtags -p - mymethod
- List all tags matching "mymethod", case insensitively:
$ readtags -i - mymethod
- List all tags start with "myvar", and printing all fields (i.e., the whole line):
$ readtags -p -ne - myvar
Scheme-style expressions are used for the -Q and -S options. For those who doesn't know Scheme or Lisp, just remember:
- A function call is wrapped in a pair of parenthesis. The first item in it is the function/operator name, the others are arguments.
- Function calls can be nested.
So, (+ 1 (+ 2 3)) means add 2 and 3 first, then add the result with 1.
The tag entries that makes the filter expression produces non-#f values are filtered out (#f means false).
The basic operators for filtering are eq?, prefix?, suffix?, substr?, and #/PATTERN/. Language common fields can be accessed using variables starting with $, e.g., $language represents the language field. For example:
- List all tags start with "myfunc" in Python code files:
$ readtags -p -Q '(eq? $language "Python")' - myfunc
downcase or upcase operators can be used to perform case-insensitive matching:
- List all tags containing "my", case insensitively:
$ readtags -Q '(substr? (downcase $name) "my")' -l
We have logical operators like and, or and not. The value of a missing field is #f, so we could deal with missing fields:
- List all tags containing "impl" in Python code files, but allow the language: field to be missing:
$ readtags -Q '(and (substr? $name "impl")\
(or (eq? $language "Python")\
(not $language)))' -l
#/PATTERN/ is for the case when string predicates (prefix?, suffix, and substr?) are not enough. You can use "Posix extended regular expression" as PATTERN.
- List all tags inherits from the class "A":
$ readtags -Q '(#/(^|, )A(,|$)/ $inherits)' -l
Here $inherits is a comma-separated class list like "A, B, C", "Z, A", "P, A, Q", or just "A". The tags file may have tag entries that has no inherits: field. In that case $inherits is #f, and the regular expression matching raises an error, since it works only for strings. To avoid this problem:
- Safely list all tags inherits from the class "A":
$ readtags -Q '(and $inherits (#/(^|, )A(,|$)/ $inherits))' -l
Case-insensitive matching can be performed by #/PATTERN/i.
- Safely list all tags inherits from the class "A" or "a":
$ readtags -Q '(and $inherits (#/(^|, )A(,|$)/i $inherits))' -l
To include "/" in a pattern, prefix "" to the "/".
NOTE: The above regular expression pattern for inspecting inheritances is just an example to show how to use #/PATTERN/ expression. Tags file generators have no consensus about the format of inherits:. Even parsers in ctags have no consensus. Noticing the format of the inherits: field of specific languages is needed for such queries.
The expressions #/PATTERN/ and #/PATTERN/i are for interactive use. Readtags also offers an alias string->regexp, so #/PATTERN/ is equal to (string->regexp "PATTERN"), and #/PATTERN/i is equal to (string->regexp "PATTERN" :case-fold #t). string->regexp doesn't need to prefix "" for including "/" in a pattern. string->regexp may simplify a client tool building an expression. See also ctags-client-tools(7) for making an expression in your tool.
Run "readtags -H filter" to know about all valid functions and variables.
When sorting, the sorter expression is evaluated on two tag entries to decide which should sort before the other one, until the order of all tag entries is decided.
In a sorter expression, $ and & are used to access the fields in the two tag entries, and let's call them $-entry and &-entry. The sorter expression should have a value of -1, 0 or 1. The value -1 means the $-entry should sort before the &-entry, 1 means the contrary, and 0 makes their order in the output uncertain.
The core operator of sorting is <>. It's used to compare two strings or two numbers (numbers are for the line: or end: fields). In (<> a b), if a < b, the result is -1; a > b produces 1, and a = b produces 0. Strings are compared using the strcmp function, see strcmp(3).
For example, sort by names, and make those shorter or alphabetically smaller ones appear before the others:
$ readtags -S '(<> $name &name)' -l
This reads "If the tag name in the $-entry is smaller, it goes before the &-entry".
The <or> operator is used to chain multiple expressions until one returns -1. For example, sort by input file names, then line numbers if in the same file:
$ readtags -S '(<or> (<> $input &input) (<> $line &line))' -l
The *- operator is used to flip the compare result. i.e., (*- (<> a b)) is the same as (<> b a).
Inspecting the Behavior of Expressions¶
The print operator can be used to print the value of an expression. For example:
$ readtags -Q '(print $name)' -l
prints the name of each tag entry before it. Since the return value of print is not #f, all the tag entries are printed. We could control this using the begin or begin0 operator. begin returns the value of its last argument, and begin0 returns the value of its first argument. For example:
$ readtags -Q '(begin0 #f (print (prefix? "ctags" "ct")))' -l
prints a bunch of "#t" (depending on how many lines are in the tags file), and the actual tag entries are not printed.
Sometimes readtags exits with status 0 even when an error occurs, e.g., when a directory is passed to the -t option.
See tags(5) for the details of tags file format.
See ctags-client-tools(7) for the tips writing a tool utilizing tags file.
The official Universal-ctags web site at:
The git repository for the library used in readtags command:
Universal-ctags project https://ctags.io/
Darren Hiebert <firstname.lastname@example.org> http://DarrenHiebert.com/
The readtags command and libreadtags maintained at Universal-ctags are derived from readtags.c and readtags.h developd at http://ctags.sourceforge.net.