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<div class="document" id="readtags">
<span id="readtags-1"></span>
<h1 class="title">readtags</h1>
<h2 class="subtitle" id="find-tag-file-entries-matching-specified-names">Find tag file entries matching specified names</h2>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Version:</th>
<td>5.9.0</td></tr>
<tr class="manual-group field"><th class="docinfo-name">Manual group:</th><td class="field-body">Universal Ctags</td>
</tr>
<tr class="manual-section field"><th class="docinfo-name">Manual section:</th><td class="field-body">1</td>
</tr>
</tbody>
</table>
<div class="section" id="synopsis">
<h1>SYNOPSIS</h1>
<div class="line-block">
<div class="line"><strong>readtags</strong> -h | --help</div>
<div class="line"><strong>readtags</strong> (-H | --help-expression) (filter|sorter)</div>
<div class="line"><strong>readtags</strong> [OPTION]... ACTION</div>
</div>
</div>
<div class="section" id="description">
<h1>DESCRIPTION</h1>
<p>The <strong>readtags</strong> program filters, sorts and prints tag entries in a tags file.
The basic filtering is done using <strong>actions</strong>, 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 <strong>post processors</strong>, namely <strong>filter
expressions</strong> and <strong>sorter expressions</strong>.</p>
</div>
<div class="section" id="actions">
<h1>ACTIONS</h1>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">-l</span></tt>, <tt class="docutils literal"><span class="pre">--list</span></tt></dt>
<dd>List regular tags.</dd>
<dt><tt class="docutils literal"><span class="pre">[-]</span> NAME</tt></dt>
<dd>List regular tags matching NAME.
"-" as NAME indicates arguments after this as NAME even if they start with -.</dd>
<dt><tt class="docutils literal"><span class="pre">-D</span></tt>, <tt class="docutils literal"><span class="pre">--list-pseudo-tags</span></tt></dt>
<dd>Equivalent to <tt class="docutils literal"><span class="pre">--list-pseudo-tags</span></tt>.</dd>
</dl>
</div>
<div class="section" id="options">
<h1>OPTIONS</h1>
<div class="section" id="controlling-the-tags-reading-behavior">
<h2>Controlling the Tags Reading Behavior</h2>
<p>The behavior of reading tags can be controlled using these options:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">-t</span> TAGFILE</tt>, <tt class="docutils literal"><span class="pre">--tag-file</span> TAGFILE</tt></dt>
<dd>Use specified tag file (default: "tags").</dd>
<dt><tt class="docutils literal"><span class="pre">-s[0|1|2]</span></tt>, <tt class="docutils literal"><span class="pre">--override-sort-detection</span> METHOD</tt></dt>
<dd>Override sort detection of tag file.
METHOD: unsorted|sorted|foldcase</dd>
</dl>
<p>The NAME action will perform binary search on sorted (including "foldcase")
tags files, which is much faster then on unsorted tags files.</p>
</div>
<div class="section" id="controlling-the-name-action-behavior">
<h2>Controlling the NAME Action Behavior</h2>
<p>The behavior of the NAME action can be controlled using these options:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">-i</span></tt>, <tt class="docutils literal"><span class="pre">--icase-match</span></tt></dt>
<dd>Perform case-insensitive matching in the NAME action.</dd>
<dt><tt class="docutils literal"><span class="pre">-p</span></tt>, <tt class="docutils literal"><span class="pre">--prefix-match</span></tt></dt>
<dd>Perform prefix matching in the NAME action.</dd>
</dl>
</div>
<div class="section" id="controlling-the-output">
<h2>Controlling the Output</h2>
<p>By default, the output of readtags contains only the name, input and pattern
field. The Output can be tweaked using these options:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">-d</span></tt>, <tt class="docutils literal"><span class="pre">--debug</span></tt></dt>
<dd>Turn on debugging output.</dd>
<dt><tt class="docutils literal"><span class="pre">-E</span></tt>, <tt class="docutils literal"><span class="pre">--escape-output</span></tt></dt>
<dd>Escape characters like tabs in output as described in tags(5).</dd>
<dt><tt class="docutils literal"><span class="pre">-e</span></tt>, <tt class="docutils literal"><span class="pre">--extension-fields</span></tt></dt>
<dd>Include extension fields in output.</dd>
<dt><tt class="docutils literal"><span class="pre">-n</span></tt>, <tt class="docutils literal"><span class="pre">--line-number</span></tt></dt>
<dd>Also include the line number field when <tt class="docutils literal"><span class="pre">-e</span></tt> option is give.</dd>
</dl>
<p>About the <tt class="docutils literal"><span class="pre">-E</span></tt> 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, <tt class="docutils literal"><span class="pre">-E</span></tt> option should be used. See ctags-client-tools(7) for more
discussion on this.</p>
</div>
<div class="section" id="filtering-and-sorting">
<h2>Filtering and Sorting</h2>
<p>Further filtering and sorting on the tags listed by actions are performed using:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">-Q</span> EXP</tt>, <tt class="docutils literal"><span class="pre">--filter</span> EXP</tt></dt>
<dd>Filter the tags listed by ACTION with EXP before printing.</dd>
<dt><tt class="docutils literal"><span class="pre">-S</span> EXP</tt>, <tt class="docutils literal"><span class="pre">--sorter</span> EXP</tt></dt>
<dd>Sort the tags listed by ACTION with EXP before printing.</dd>
</dl>
<p>These are discussed in the <a class="reference internal" href="#expression">EXPRESSION</a> section.</p>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<ul>
<li><p class="first">List all tags in "/path/to/tags":</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -t /path/to/tags -l
</pre>
</li>
<li><p class="first">List all tags in "tags" that start with "mymethod":</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -p - mymethod
</pre>
</li>
<li><p class="first">List all tags matching "mymethod", case insensitively:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -i - mymethod
</pre>
</li>
<li><p class="first">List all tags start with "myvar", and printing all fields (i.e., the whole line):</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -p -ne - myvar
</pre>
</li>
</ul>
</div>
</div>
<div class="section" id="expression">
<h1>EXPRESSION</h1>
<p>Scheme-style expressions are used for the <tt class="docutils literal"><span class="pre">-Q</span></tt> and <tt class="docutils literal"><span class="pre">-S</span></tt> options. For those
who doesn't know Scheme or Lisp, just remember:</p>
<ul class="simple">
<li>A function call is wrapped in a pair of parenthesis. The first item in it is
the function/operator name, the others are arguments.</li>
<li>Function calls can be nested.</li>
<li>Missing values and boolean false are represented by <tt class="docutils literal">#f</tt>. <tt class="docutils literal">#t</tt> and all
other values are considered to be true.</li>
</ul>
<p>So, <tt class="docutils literal">(+ 1 (+ 2 3))</tt> means add 2 and 3 first, then add the result with 1.
<tt class="docutils literal">(and "string" 1 #t)</tt> means logical AND on <tt class="docutils literal">"string"</tt>, <tt class="docutils literal">1</tt> and <tt class="docutils literal">#t</tt>,
and the result is true since there is no <tt class="docutils literal">#f</tt>.</p>
<div class="section" id="filtering">
<h2>Filtering</h2>
<p>The tag entries that make the filter expression produces true value are printed
by readtags.</p>
<p>The basic operators for filtering are <tt class="docutils literal">eq?</tt>, <tt class="docutils literal">prefix?</tt>, <tt class="docutils literal">suffix?</tt>,
<tt class="docutils literal">substr?</tt>, and <tt class="docutils literal">#/PATTERN/</tt>. Language common fields can be accessed using
variables starting with <tt class="docutils literal">$</tt>, e.g., <tt class="docutils literal">$language</tt> represents the language field.
For example:</p>
<ul>
<li><p class="first">List all tags start with "myfunc" in Python code files:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -p -Q <span class="literal string single">'(eq? $language "Python")'</span> - myfunc
</pre>
</li>
</ul>
<p><tt class="docutils literal">downcase</tt> or <tt class="docutils literal">upcase</tt> operators can be used to perform case-insensitive
matching:</p>
<ul>
<li><p class="first">List all tags containing "my", case insensitively:</p>
<blockquote>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(substr? (downcase $name) "my")'</span> -l
</pre>
</blockquote>
</li>
</ul>
<p>We have logical operators like <tt class="docutils literal">and</tt>, <tt class="docutils literal">or</tt> and <tt class="docutils literal">not</tt>. The value of a
missing field is #f, so we could deal with missing fields:</p>
<ul>
<li><p class="first">List all tags containing "impl" in Python code files, but allow the
<tt class="docutils literal">language:</tt> field to be missing:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="error">'</span><span class="operator">(</span>and <span class="operator">(</span>substr? <span class="name variable">$name</span> <span class="literal string double">"impl"</span><span class="operator">)</span><span class="literal string escape">\
</span><span class="generic output"> (or (not $language)\
(eq? $language "Python")))' -l</span>
</pre>
</li>
</ul>
<p><tt class="docutils literal">#/PATTERN/</tt> is for the case when string predicates (<tt class="docutils literal">prefix?</tt>, <tt class="docutils literal">suffix?</tt>,
and <tt class="docutils literal">substr?</tt>) are not enough. You can use "Posix extended regular expression"
as PATTERN.</p>
<ul>
<li><p class="first">List all tags inherits from the class "A":</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(#/(^|,) ?A(,|$)/ $inherits)'</span> -l
</pre>
</li>
</ul>
<p>Here <tt class="docutils literal">$inherits</tt> is a comma-separated class list like "A,B,C", "P, A, Q", or
just "A". Notice that this filter works on both situations where there's a
space after each comma or there's not.</p>
<p>Case-insensitive matching can be performed by <tt class="docutils literal">#/PATTERN/i</tt>:</p>
<ul>
<li><p class="first">List all tags inherits from the class "A" or "a":</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(#/(^|,) ?A(,|$)/i $inherits)'</span> -l
</pre>
</li>
</ul>
<p>To include "/" in a pattern, prefix <tt class="docutils literal">\</tt> to the "/".</p>
<p>NOTE: The above regular expression pattern for inspecting inheritances is just
an example to show how to use <tt class="docutils literal">#/PATTERN/</tt> expression. Tags file generators
have no consensus about the format of <tt class="docutils literal">inherits:</tt>, e.g., whether there should
be a space after a comma. Even parsers in ctags have no consensus. Noticing the
format of the <tt class="docutils literal">inherits:</tt> field of specific languages is needed for such
queries.</p>
<p>The expressions <tt class="docutils literal">#/PATTERN/</tt> and <tt class="docutils literal">#/PATTERN/i</tt> are for interactive use.
Readtags also offers an alias <tt class="docutils literal"><span class="pre">string->regexp</span></tt>, so <tt class="docutils literal">#/PATTERN/</tt> is equal to
<tt class="docutils literal"><span class="pre">(string->regexp</span> "PATTERN")</tt>, and <tt class="docutils literal">#/PATTERN/i</tt> is equal to
<tt class="docutils literal"><span class="pre">(string->regexp</span> "PATTERN" <span class="pre">:case-fold</span> #t)</tt>. <tt class="docutils literal"><span class="pre">string->regexp</span></tt> doesn't need
to prefix <tt class="docutils literal">\</tt> for including "/" in a pattern. <tt class="docutils literal"><span class="pre">string->regexp</span></tt> may simplify
a client tool building an expression. See also ctags-client-tools(7) for
building expressions in your tool.</p>
<p>Let's now consider missing fields. The tags file may have tag entries that has
no <tt class="docutils literal">inherits:</tt> field. In that case <tt class="docutils literal">$inherits</tt> is #f, and the regular
expression matching raises an error, since string operators only work for
strings. To avoid this problem:</p>
<ul>
<li><p class="first">Safely list all tags inherits from the class "A":</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(and $inherits (#/(^|,) ?A(,|$)/ $inherits))'</span> -l
</pre>
</li>
</ul>
<p>This makes sure <tt class="docutils literal">$inherits</tt> is not missing first, then match it by regexp.</p>
<p>Sometimes you want to keep tags where the field <em>is</em> missing. For example, your
want to exclude reference tags, which is marked by the <tt class="docutils literal">extras:</tt> field, then
you want to keep tags who doesn't have <tt class="docutils literal">extras:</tt> field since they are also
not reference tags. Here's how to do it:</p>
<ul>
<li><p class="first">List all tags but the reference tags:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(or (not $extras) (#/(^|,) ?reference(,|$)/ $extras))'</span> -l
</pre>
</li>
</ul>
<p>Notice that <tt class="docutils literal">(not $extras)</tt> produces <tt class="docutils literal">#t</tt> when <tt class="docutils literal">$extras</tt> is missing, so
the whole <tt class="docutils literal">or</tt> expression produces <tt class="docutils literal">#t</tt>.</p>
<p>Run "readtags -H filter" to know about all valid functions and variables.</p>
</div>
<div class="section" id="sorting">
<h2>Sorting</h2>
<p>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.</p>
<p>In a sorter expression, <tt class="docutils literal">$</tt> and <tt class="docutils literal">&</tt> 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 $-entry should be put
above the &-entry, 1 means the contrary, and 0 makes their order in the output
uncertain.</p>
<p>The core operator of sorting is <tt class="docutils literal"><></tt>. It's used to compare two strings or two
numbers (numbers are for the <tt class="docutils literal">line:</tt> or <tt class="docutils literal">end:</tt> fields). In <tt class="docutils literal">(<> a b)</tt>, if
<tt class="docutils literal">a</tt> < <tt class="docutils literal">b</tt>, the result is -1; <tt class="docutils literal">a</tt> > <tt class="docutils literal">b</tt> produces 1, and <tt class="docutils literal">a</tt> = <tt class="docutils literal">b</tt>
produces 0. Strings are compared using the <tt class="docutils literal">strcmp</tt> function, see strcmp(3).</p>
<p>For example, sort by names, and make those shorter or alphabetically smaller
ones appear before the others:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -S <span class="literal string single">'(<> $name &name)'</span> -l
</pre>
<p>This reads "If the tag name in the $-entry is smaller, it goes before the
&-entry".</p>
<p>The <tt class="docutils literal"><or></tt> operator is used to chain multiple expressions until one returns
-1 or 1. For example, sort by input file names, then line numbers if in the
same file:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -S <span class="literal string single">'(<or> (<> $input &input) (<> $line &line))'</span> -l
</pre>
<p>The <tt class="docutils literal">*-</tt> operator is used to flip the compare result. i.e., <tt class="docutils literal">(*- (<> a b))</tt>
is the same as <tt class="docutils literal">(<> b a)</tt>.</p>
<p>Filter expressions can be used in sorter expressions. The technique is use
<tt class="docutils literal">if</tt> to produce integers that can be compared based on the filter, like:</p>
<pre class="code lisp literal-block">
<span class="punctuation">(</span><span class="name variable"><></span> <span class="punctuation">(</span><span class="keyword">if</span> <span class="name variable">filter-expr-on-$-entry</span> <span class="literal number integer">-1</span> <span class="literal number integer">1</span><span class="punctuation">)</span>
<span class="punctuation">(</span><span class="keyword">if</span> <span class="name variable">filter-expr-on-&-entry</span> <span class="literal number integer">-1</span> <span class="literal number integer">1</span><span class="punctuation">))</span>
</pre>
<p>So if $-entry satisfies the filter, while &-entry doesn't, it's the same as
<tt class="docutils literal">(<> <span class="pre">-1</span> 1)</tt>, which produces <tt class="docutils literal"><span class="pre">-1</span></tt>.</p>
<p>For example, we want to put tags with "file" kind below other tags, then the
sorter would look like:</p>
<pre class="code lisp literal-block">
<span class="punctuation">(</span><span class="name variable"><></span> <span class="punctuation">(</span><span class="keyword">if</span> <span class="punctuation">(</span><span class="name variable">eq?</span> <span class="name variable">$kind</span> <span class="literal string">"file"</span><span class="punctuation">)</span> <span class="literal number integer">1</span> <span class="literal number integer">-1</span><span class="punctuation">)</span>
<span class="punctuation">(</span><span class="keyword">if</span> <span class="punctuation">(</span><span class="name variable">eq?</span> <span class="name variable">&kind</span> <span class="literal string">"file"</span><span class="punctuation">)</span> <span class="literal number integer">1</span> <span class="literal number integer">-1</span><span class="punctuation">))</span>
</pre>
<p>A quick read tells us: If $-entry has "file" kind, and &-entry doesn't, the
sorter becomes <tt class="docutils literal">(<> 1 <span class="pre">-1)</span></tt>, which produces <tt class="docutils literal">1</tt>, so the $-entry is put below
the &-entry, exactly what we want.</p>
</div>
<div class="section" id="inspecting-the-behavior-of-expressions">
<h2>Inspecting the Behavior of Expressions</h2>
<p>The <cite>print</cite> operator can be used to print the value of an expression. For
example:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(print $name)'</span> -l
</pre>
<p>prints the name of each tag entry before it. Since the return value of
<tt class="docutils literal">print</tt> is not #f, all the tag entries are printed. We could control this
using the <tt class="docutils literal">begin</tt> or <tt class="docutils literal">begin0</tt> operator. <tt class="docutils literal">begin</tt> returns the value of its
last argument, and <tt class="docutils literal">begin0</tt> returns the value of its first argument. For
example:</p>
<pre class="code console literal-block">
<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(begin0 #f (print (prefix? "ctags" "ct")))'</span> -l
</pre>
<p>prints a bunch of "#t" (depending on how many lines are in the tags file), and
the actual tag entries are not printed.</p>
</div>
</div>
<div class="section" id="see-also">
<h1>SEE ALSO</h1>
<p>See tags(5) for the details of tags file format.</p>
<p>See ctags-client-tools(7) for the tips writing a
tool utilizing tags file.</p>
<p>The official Universal Ctags web site at:</p>
<p><a class="reference external" href="https://ctags.io/">https://ctags.io/</a></p>
<p>The git repository for the library used in readtags command:</p>
<p><a class="reference external" href="https://github.com/universal-ctags/libreadtags">https://github.com/universal-ctags/libreadtags</a></p>
</div>
<div class="section" id="credits">
<h1>CREDITS</h1>
<p>Universal Ctags project
<a class="reference external" href="https://ctags.io/">https://ctags.io/</a></p>
<p>Darren Hiebert <<a class="reference external" href="mailto:dhiebert@users.sourceforge.net">dhiebert@users.sourceforge.net</a>>
<a class="reference external" href="http://DarrenHiebert.com/">http://DarrenHiebert.com/</a></p>
<p>The readtags command and libreadtags maintained at Universal Ctags
are derived from readtags.c and readtags.h developd at
<a class="reference external" href="http://ctags.sourceforge.net">http://ctags.sourceforge.net</a>.</p>
</div>
</div>
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