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authorIndrajith K L2022-12-03 17:00:20 +0530
committerIndrajith K L2022-12-03 17:00:20 +0530
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tree2764fc62da58f2ba8da7ed341643fc359873142f /ctags/man/readtags.1.html
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+</style>
+</head>
+<body>
+<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.
+&quot;-&quot; 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: &quot;tags&quot;).</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 &quot;foldcase&quot;)
+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 &quot;/path/to/tags&quot;:</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 &quot;tags&quot; that start with &quot;mymethod&quot;:</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 &quot;mymethod&quot;, 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 &quot;myvar&quot;, 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 &quot;string&quot; 1 #t)</tt> means logical AND on <tt class="docutils literal">&quot;string&quot;</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 &quot;myfunc&quot; 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? $language &quot;Python&quot;)'</span> - myfunc
+</pre>
+</li>
+</ul>
+<p><tt class="docutils literal">downcase</tt> or <tt class="docutils literal">upcase</tt> operators can be used to perform case-insensitive
+matching:</p>
+<ul>
+<li><p class="first">List all tags containing &quot;my&quot;, case insensitively:</p>
+<blockquote>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(substr? (downcase $name) &quot;my&quot;)'</span> -l
+</pre>
+</blockquote>
+</li>
+</ul>
+<p>We have logical operators like <tt class="docutils literal">and</tt>, <tt class="docutils literal">or</tt> and <tt class="docutils literal">not</tt>. The value of a
+missing field is #f, so we could deal with missing fields:</p>
+<ul>
+<li><p class="first">List all tags containing &quot;impl&quot; in Python code files, but allow the
+<tt class="docutils literal">language:</tt> field to be missing:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </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">&quot;impl&quot;</span><span class="operator">)</span><span class="literal string escape">\
+</span><span class="generic output"> (or (not $language)\
+ (eq? $language &quot;Python&quot;)))' -l</span>
+</pre>
+</li>
+</ul>
+<p><tt class="docutils literal">#/PATTERN/</tt> is for the case when string predicates (<tt class="docutils literal">prefix?</tt>, <tt class="docutils literal">suffix?</tt>,
+and <tt class="docutils literal">substr?</tt>) are not enough. You can use &quot;Posix extended regular expression&quot;
+as PATTERN.</p>
+<ul>
+<li><p class="first">List all tags inherits from the class &quot;A&quot;:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </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 &quot;A,B,C&quot;, &quot;P, A, Q&quot;, or
+just &quot;A&quot;. 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 &quot;A&quot; or &quot;a&quot;:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </span>readtags -Q <span class="literal string single">'(#/(^|,) ?A(,|$)/i $inherits)'</span> -l
+</pre>
+</li>
+</ul>
+<p>To include &quot;/&quot; in a pattern, prefix <tt class="docutils literal">\</tt> to the &quot;/&quot;.</p>
+<p>NOTE: The above regular expression pattern for inspecting inheritances is just
+an example to show how to use <tt class="docutils literal">#/PATTERN/</tt> expression. Tags file generators
+have no consensus about the format of <tt class="docutils literal">inherits:</tt>, e.g., whether there should
+be a space after a comma. Even parsers in ctags have no consensus. Noticing the
+format of the <tt class="docutils literal">inherits:</tt> field of specific languages is needed for such
+queries.</p>
+<p>The expressions <tt class="docutils literal">#/PATTERN/</tt> and <tt class="docutils literal">#/PATTERN/i</tt> are for interactive use.
+Readtags also offers an alias <tt class="docutils literal"><span class="pre">string-&gt;regexp</span></tt>, so <tt class="docutils literal">#/PATTERN/</tt> is equal to
+<tt class="docutils literal"><span class="pre">(string-&gt;regexp</span> &quot;PATTERN&quot;)</tt>, and <tt class="docutils literal">#/PATTERN/i</tt> is equal to
+<tt class="docutils literal"><span class="pre">(string-&gt;regexp</span> &quot;PATTERN&quot; <span class="pre">:case-fold</span> #t)</tt>. <tt class="docutils literal"><span class="pre">string-&gt;regexp</span></tt> doesn't need
+to prefix <tt class="docutils literal">\</tt> for including &quot;/&quot; in a pattern. <tt class="docutils literal"><span class="pre">string-&gt;regexp</span></tt> may simplify
+a client tool building an expression. See also ctags-client-tools(7) for
+building expressions in your tool.</p>
+<p>Let's now consider missing fields. The tags file may have tag entries that has
+no <tt class="docutils literal">inherits:</tt> field. In that case <tt class="docutils literal">$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 &quot;A&quot;:</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 &quot;readtags -H filter&quot; 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">&amp;</tt> are used to access the fields in the
+two tag entries, and let's call them $-entry and &amp;-entry. The sorter expression
+should have a value of -1, 0 or 1. The value -1 means the $-entry should be put
+above the &amp;-entry, 1 means the contrary, and 0 makes their order in the output
+uncertain.</p>
+<p>The core operator of sorting is <tt class="docutils literal">&lt;&gt;</tt>. It's used to compare two strings or two
+numbers (numbers are for the <tt class="docutils literal">line:</tt> or <tt class="docutils literal">end:</tt> fields). In <tt class="docutils literal">(&lt;&gt; a b)</tt>, if
+<tt class="docutils literal">a</tt> &lt; <tt class="docutils literal">b</tt>, the result is -1; <tt class="docutils literal">a</tt> &gt; <tt class="docutils literal">b</tt> produces 1, and <tt class="docutils literal">a</tt> = <tt class="docutils literal">b</tt>
+produces 0. Strings are compared using the <tt class="docutils literal">strcmp</tt> function, see strcmp(3).</p>
+<p>For example, sort by names, and make those shorter or alphabetically smaller
+ones appear before the others:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </span>readtags -S <span class="literal string single">'(&lt;&gt; $name &amp;name)'</span> -l
+</pre>
+<p>This reads &quot;If the tag name in the $-entry is smaller, it goes before the
+&amp;-entry&quot;.</p>
+<p>The <tt class="docutils literal">&lt;or&gt;</tt> operator is used to chain multiple expressions until one returns
+-1 or 1. For example, sort by input file names, then line numbers if in the
+same file:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </span>readtags -S <span class="literal string single">'(&lt;or&gt; (&lt;&gt; $input &amp;input) (&lt;&gt; $line &amp;line))'</span> -l
+</pre>
+<p>The <tt class="docutils literal">*-</tt> operator is used to flip the compare result. i.e., <tt class="docutils literal">(*- (&lt;&gt; a b))</tt>
+is the same as <tt class="docutils literal">(&lt;&gt; b a)</tt>.</p>
+<p>Filter expressions can be used in sorter expressions. The technique is use
+<tt class="docutils literal">if</tt> to produce integers that can be compared based on the filter, like:</p>
+<pre class="code lisp literal-block">
+<span class="punctuation">(</span><span class="name variable">&lt;&gt;</span> <span class="punctuation">(</span><span class="keyword">if</span> <span class="name variable">filter-expr-on-$-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-&amp;-entry</span> <span class="literal number integer">-1</span> <span class="literal number integer">1</span><span class="punctuation">))</span>
+</pre>
+<p>So if $-entry satisfies the filter, while &amp;-entry doesn't, it's the same as
+<tt class="docutils literal">(&lt;&gt; <span class="pre">-1</span> 1)</tt>, which produces <tt class="docutils literal"><span class="pre">-1</span></tt>.</p>
+<p>For example, we want to put tags with &quot;file&quot; kind below other tags, then the
+sorter would look like:</p>
+<pre class="code lisp literal-block">
+<span class="punctuation">(</span><span class="name variable">&lt;&gt;</span> <span class="punctuation">(</span><span class="keyword">if</span> <span class="punctuation">(</span><span class="name variable">eq?</span> <span class="name variable">$kind</span> <span class="literal string">&quot;file&quot;</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">&amp;kind</span> <span class="literal string">&quot;file&quot;</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 &quot;file&quot; kind, and &amp;-entry doesn't, the
+sorter becomes <tt class="docutils literal">(&lt;&gt; 1 <span class="pre">-1)</span></tt>, which produces <tt class="docutils literal">1</tt>, so the $-entry is put below
+the &amp;-entry, exactly what we want.</p>
+</div>
+<div class="section" id="inspecting-the-behavior-of-expressions">
+<h2>Inspecting the Behavior of Expressions</h2>
+<p>The <cite>print</cite> operator can be used to print the value of an expression. For
+example:</p>
+<pre class="code console literal-block">
+<span class="generic prompt">$ </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? &quot;ctags&quot; &quot;ct&quot;)))'</span> -l
+</pre>
+<p>prints a bunch of &quot;#t&quot; (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 &lt;<a class="reference external" href="mailto:dhiebert&#64;users.sourceforge.net">dhiebert&#64;users.sourceforge.net</a>&gt;
+<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>
+</body>
+</html>