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<a href="#NAME">NAME</a>
<a href="#SYNOPSIS">SYNOPSIS</a>
<a href="#DESCRIPTION">DESCRIPTION</a>
<a href="#OPTIONS">OPTIONS</a>
<a href="#OPERATION">OPERATION</a>
<a href="#COMMANDS">COMMANDS</a>
<a href="#OUTPUT-FORMAT">OUTPUT FORMAT</a>
<a href="#EXIT-STATUS">EXIT STATUS</a>
<a href="#EXAMPLES">EXAMPLES</a>
<a href="#SEE-ALSO">SEE ALSO</a>
<a href="#BUGS">BUGS</a>
<a href="#COPYRIGHT">COPYRIGHT</a>
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<li class='tl'>jt(1)</li>
<li class='tc'>JT MANUAL</li>
<li class='tr'>jt(1)</li>
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<h2 id="NAME">NAME</h2>
<p class="man-name">
<code>jt</code> - <span class="man-whatis">transform JSON data to tabular format</span>
</p>
<h2 id="SYNOPSIS">SYNOPSIS</h2>
<p><code>jt</code> <code>[-hV]</code><br />
<code>jt</code> <code>-u</code> <var>string</var><br />
<code>jt</code> [<code>-acj</code>] [<code>COMMAND</code> ...]</p>
<h2 id="DESCRIPTION">DESCRIPTION</h2>
<p><strong>Jt</strong> reads UTF-8 encoded JSON forms from <var>stdin</var> and writes tab separated
values (or CSV) to <var>stdout</var>. A simple stack-based programming language is used
to extract values from the JSON input for printing.</p>
<h2 id="OPTIONS">OPTIONS</h2>
<dl>
<dt class="flush"><code>-h</code></dt><dd><p>Print usage info and exit.</p></dd>
<dt class="flush"><code>-V</code></dt><dd><p>Print version and license info and exit.</p></dd>
<dt class="flush"><code>-a</code></dt><dd><p>Explicit iteration mode: require the <code>.</code> command to iterate over arrays
instead of iterating automatically.</p></dd>
<dt class="flush"><code>-c</code></dt><dd><p>CSV output mode: write RFC 4180 compliant CSV records.</p></dd>
<dt class="flush"><code>-j</code></dt><dd><p>Inner join mode: discard rows with missing columns.</p></dd>
<dt class="flush"><code>-s</code></dt><dd><p>A no-op, included for compatibility with earlier versions.</p></dd>
<dt><code>-u</code> <var>string</var></dt><dd><p>Unescape JSON <var>string</var>, print it, and exit. Double-quotes around <var>string</var>
are optional.</p></dd>
</dl>
<h2 id="OPERATION">OPERATION</h2>
<p>Non-option arguments are words (commands) in a stack-based programming language.
Commands operate on the stacks provided by the <strong>jt</strong> runtime:</p>
<ul>
<li><p>The <code>DATA</code> stack contains JSON values commands will operate on.</p></li>
<li><p>The <code>GOSUB</code> stack contains pointers into the data stack.</p></li>
<li><p>The <code>INDEX</code> stack contains pointers to iterators during iteration.</p></li>
<li><p>The <code>LOOP</code> stack contains pointers to iterators between iterations.</p></li>
<li><p>The <code>OUTPUT</code> stack contains values to print after each iteration.</p></li>
</ul>
<p>When <strong>jt</strong> starts, the following happens:</p>
<ol>
<li><p>One JSON form is read from <var>stdin</var>, parsed, and pushed onto the data stack.</p></li>
<li><p>If the top of the data stack is a JSON array the next item in the array is
pushed onto the data stack based on state previously saved on the loop stack.
The loop stack is then popped and pushed onto the index stack.</p></li>
<li><p>The next command is executed.</p></li>
<li><p>Steps 2 and 3 are repeated until no commands are left to execute.</p></li>
<li><p>Values in the output stack are printed, separated by tabs and followed by a
newline (see <strong>OUTPUT FORMAT</strong> below). Data, output, and gosub stacks are
reset to their states as they were after step 1.</p></li>
<li><p>Loop variables are popped off of the index stack. They are then incremented
and pushed onto the loop stack as necessary.</p></li>
<li><p>Steps 2 through 6 are repeated until the loop stack is empty (i.e. there are
no more iterations left).</p></li>
</ol>
<p>This process is repeated until there is no more JSON to read.</p>
<h2 id="COMMANDS">COMMANDS</h2>
<p><strong>Jt</strong> provides the following commands:</p>
<dl>
<dt class="flush"><code>[</code></dt><dd><p>Save the state of the data stack: the current data stack pointer is pushed
onto the gosub stack.</p></dd>
<dt class="flush"><code>]</code></dt><dd><p>Restore the data stack to a saved state: pop the gosub stack and restore
the data stack pointer to that state.</p></dd>
<dt class="flush"><code>%</code></dt><dd><p>Push the value at the top of the data stack onto the output stack.</p></dd>
<dt class="flush"><code>%=</code><var>NAME</var></dt><dd><p>Like <code>%</code>, but also sets the heading for this column to <var>NAME</var>. Headers
will be printed as the first line of output when this command has been used.</p></dd>
<dt class="flush"><code>^</code></dt><dd><p>Push the value at the top of the index stack onto the output stack. Note
that the index stack will always have at least one item: the index of the
last JSON object read from stdin.</p></dd>
<dt class="flush"><code>^=</code><var>NAME</var></dt><dd><p>Like <code>^</code>, but also sets the heading for this column to <var>NAME</var>. Headers
will be printed as the first line of output when this command has been used.</p></dd>
<dt class="flush"><code>@</code></dt><dd><p>Print the keys of the object at the top of the data stack and exit.</p>
<p>If the value at the top of the data stack is an array the first item in the
array is pushed onto the data stack and the command is reevaluated.</p>
<p>If the value at the top of the data stack is not an object or an array then
its type is printed in brackets, eg. <var>[array]</var>, <var>[string]</var>, <var>[number]</var>,
<var>[boolean]</var>, or <var>[null]</var>. If there is no value then <var>[none]</var> is printed.</p></dd>
<dt class="flush"><code>+</code></dt><dd><p>Parse embedded JSON: if the item at the top of the data stack is a string,
parse it and push the result onto the data stack.</p>
<p>If the item at the top of the data stack is not a string or if there is an
error parsing the JSON then nothing is done (the operation is a no-op).</p></dd>
<dt class="flush"><code>.</code></dt><dd><p>Iterate over the values of the object at the top of the data stack. The
current value will be pushed onto the data stack and the current key will
be pushed onto the index stack.</p></dd>
<dt class="flush"><code>[</code><var>KEY</var><code>]</code></dt><dd><p>Drill down: get the value of the <var>KEY</var> property of the object at the top
of the data stack and push that value onto the data stack.</p>
<p>If the item at the top of the data stack is not an object or if the object
has no <var>KEY</var> property a blank field is printed, unless the <code>-j</code> option was
specified in which case the entire row is removed from the output.</p>
<p>If the <var>KEY</var> property of the object is an array subsequent commands will
operate on one of the items in the array, chosen automatically by <code>jt</code>.
The array index will be available to subsequent commands via the index
stack.</p></dd>
<dt class="flush"><var>KEY</var></dt><dd><p>See <code>[</code><var>KEY</var><code>]</code> above — the <code>[</code> and <code>]</code> may be omitted if the
property name <var>KEY</var> does not conflict with any <code>jt</code> command.</p></dd>
</dl>
<h2 id="OUTPUT-FORMAT">OUTPUT FORMAT</h2>
<p>The format of printed output from <strong>jt</strong> (see <code>%</code> in <strong>COMMANDS</strong>, above)
depends on the type of thing being printed:</p>
<h3 id="Primitives">Primitives</h3>
<p>JSON primitives (i.e. <code>null</code>, <code>true</code>, and <code>false</code>) and numbers are printed
verbatim. <strong>Jt</strong> does not process them in any way. Numbers can be of arbitrary
precision, as long as they conform to the JSON parsing grammar.</p>
<p>If special formatting is required the <code>printf</code> program is your friend:</p>
<pre><code>$ printf %.0f 2.99792458e9
2997924580
</code></pre>
<h3 id="Strings">Strings</h3>
<p>Strings are printed verbatim, minus the enclosing double quotes. No unescaping
is performed because tabs or newlines in JSON strings would break the tabular
output format.</p>
<p>If unescaped values are desired either use the <code>-c</code> flag to enable CSV output
(see <strong>CSV</strong> below) or use the <code>-u</code> option and pass the string as an argument:</p>
<pre><code>$ jt -u 'i love music \u266A'
i love music ♪
</code></pre>
<h3 id="Collections">Collections</h3>
<p>Objects and arrays are printed as JSON with whitespace removed. Note that it
is only possible to print arrays when the <code>-a</code> option is specified (see the
<strong>Iteration (Arrays)</strong> and <strong>Explicit Iteration</strong> sections below).</p>
<h3 id="CSV">CSV</h3>
<p>The <code>-c</code> flag enables CSV output conforming to RFC 4180. This format supports
strings containing tabs, newlines, etc.:</p>
<pre><code>$ jt -c [ foo % ] [ bar % ] baz % <<EOT
- {
- "foo": "one\ttwo",
- "bar": "three\nfour",
- "baz": "music \"\u266A\""
- }
- EOT
"one two","three
four","music ""♪"""
</code></pre>
<h2 id="EXIT-STATUS">EXIT STATUS</h2>
<p><strong>Jt</strong> will exit with a status of 1 if an error occurred, or 0 otherwise.</p>
<h2 id="EXAMPLES">EXAMPLES</h2>
<p>Below are a number of examples demonstrating how to use <strong>jt</strong> commands to do
some simple exploration and extraction of data from JSON and JSON streams.</p>
<h3 id="Explore">Explore</h3>
<p>The <code>@</code> command prints information about the item at the top of the data stack.
When the item is an object <code>@</code> prints its keys:</p>
<pre><code class="bash">$ jt @ <<EOT
- {
- "foo": 100,
- "bar": 200,
- "baz": 300
- }
- EOT
foo
bar
baz
</code></pre>
<p>When the top item is an array <code>@</code> prints information about the first item in
the array:</p>
<pre><code class="bash">$ jt @ <<EOT
- [
- {"foo": 100, "bar": 200},
- {"baz": 300, "baf": 400}
- ]
- EOT
foo
bar
</code></pre>
<p>Otherwise, <code>@</code> prints the type of the item, or <var>[none]</var> if there is no value:</p>
<pre><code class="bash">$ echo '["hello", "world"]' | jt @
[string]
</code></pre>
<pre><code class="bash">$ echo '[1, 2]' | jt @
[number]
</code></pre>
<pre><code class="bash">$ echo '[true, false]' | jt @
[boolean]
</code></pre>
<pre><code class="bash">$ echo '[null, null]' | jt @
[null]
</code></pre>
<pre><code class="bash">$ echo '[]' | jt @
[none]
</code></pre>
<h3 id="Drill-Down">Drill Down</h3>
<p>Property names are also commands. Use <code>foo</code> here as a command to drill down
into the <var>foo</var> property and then use <code>@</code> to print its keys:</p>
<pre><code class="bash">$ jt foo @ <<EOT
- {
- "foo": {
- "bar": 100,
- "baz": 200
- }
- }
- EOT
bar
baz
</code></pre>
<p>A property name that conflicts with a <strong>jt</strong> command may be wrapped with square
brackets to drill down:</p>
<pre><code class="bash">$ jt [@] @ <<EOT
- {
- "@": {
- "bar": 100,
- "baz": 200
- }
- }
- EOT
bar
baz
</code></pre>
<p><strong>Note:</strong> The property name must be a JSON escaped string, so if the property
name in the JSON input contains eg. tab characters they must be escaped in the
command, like this:</p>
<pre><code class="bash">$ jt 'foo\tbar' @ <<EOT
- {
- "foo\tbar": {
- "bar": 100,
- "baz": 200
- }
- }
- EOT
bar
baz
</code></pre>
<h3 id="Extract">Extract</h3>
<p>The <code>%</code> command prints the item at the top of the data stack. Note that when
the top item is a collection it is printed as JSON (insiginificant whitespace
removed):</p>
<pre><code class="bash">$ jt % <<EOT
- {
- "foo": 100,
- "bar": 200
- }
- EOT
{"foo":100,"bar":200}
</code></pre>
<p>Drill down and print:</p>
<pre><code class="bash">$ jt foo bar % <<EOT
- {
- "foo": {
- "bar": 100
- }
- }
- EOT
100
</code></pre>
<p>The <code>%</code> command can be used multiple times. The printed values will be separated
by tabs:</p>
<pre><code class="bash">$ jt % foo % bar % <<EOT
- {
- "foo": {
- "bar": 100
- }
- }
- EOT
{"foo":{"bar":100}} {"bar":100} 100
</code></pre>
<h3 id="Save-Restore">Save / Restore</h3>
<p>The <code>[</code> and <code>]</code> commands provide a way to save the data stack's state before
performing some operations and restore it afterwards. This makes it possible
to drill down into one part of an object and then "rewind" to drill down into
another part of the same object.</p>
<p>The <code>[</code> command saves the state of the data stack and the <code>]</code> command restores
the data stack to the corresponding saved state. It is an error to use the <code>]</code>
command without a corresponding <code>[</code> command.</p>
<pre><code class="bash">$ jt [ foo % ] bar % <<EOT
- {
- "foo": 100,
- "bar": 200
- }
- EOT
100 200
</code></pre>
<p>The <code>[</code> and <code>]</code> commands can be nested:</p>
<pre><code class="bash">$ jt [ foo [ bar % ] [ baz % ] ] baf % <<EOT
- {
- "foo": {
- "bar": 100,
- "baz": 200
- },
- "baf": "quux"
- }
- EOT
100 200 quux
</code></pre>
<h3 id="Iteration-Arrays-">Iteration (Arrays)</h3>
<p><strong>Jt</strong> automatically iterates over arrays (unless this behavior is disabled
— see <strong>Explicit Iteration</strong> below), producing one tab-delimited record
per iteration, records separated by newlines:</p>
<pre><code class="bash">$ jt [ foo % ] bar baz % <<EOT
- {
- "foo": 100,
- "bar": [
- {"baz": 200},
- {"baz": 300},
- {"baz": 400}
- ]
- }
- EOT
100 200
100 300
100 400
</code></pre>
<p>The <code>^</code> command includes the array index as a column in the result:</p>
<pre><code class="bash">$ jt [ foo % ] bar ^ baz % <<EOT
- {
- "foo": 100,
- "bar": [
- {"baz": 200},
- {"baz": 300},
- {"baz": 400}
- ]
- }
- EOT
100 0 200
100 1 300
100 2 400
</code></pre>
<p>The <code>^</code> command is scoped to the innermost enclosing loop:</p>
<pre><code class="bash">$ jt foo ^ bar ^ % <<EOT
- {
- "foo": [
- {"bar": [100, 200]},
- {"bar": [300, 400]}
- ]
- }
- EOT
0 0 100
0 1 200
1 0 300
1 1 400
</code></pre>
<h3 id="Iteration-Objects-">Iteration (Objects)</h3>
<p>The <code>.</code> command iterates over the values of an object:</p>
<pre><code class="bash">$ jt . % <<EOT
- {
- "foo": 100,
- "bar": 200,
- "baz": 300
- }
- EOT
100
200
300
</code></pre>
<p>When iterating over an object the <code>^</code> command prints the name of the current
property:</p>
<pre><code class="bash">$ jt . ^ % <<EOT
- {
- "foo": 100,
- "bar": 200,
- "baz": 300
- }
- EOT
foo 100
bar 200
baz 300
</code></pre>
<h3 id="JSON-Streams">JSON Streams</h3>
<p><strong>Jt</strong> automatically iterates over entities in a JSON stream (optionally
delimited by whitespace):</p>
<pre><code class="bash">$ jt [ foo % ] bar % <<EOT
- {"foo": 100, "bar": 200}
- {"foo": 200, "bar": 300}
- {"foo": 300, "bar": 400}
- EOT
100 200
200 300
300 400
</code></pre>
<p>The <code>^</code> command prints the current stream index:</p>
<pre><code class="bash">$ jt ^ [ foo % ] bar % <<EOT
- {"foo": 100, "bar": 200}
- {"foo": 200, "bar": 300}
- {"foo": 300, "bar": 400}
- EOT
0 100 200
1 200 300
2 300 400
</code></pre>
<h3 id="Nested-JSON">Nested JSON</h3>
<p>The <code>+</code> command parses JSON embedded in strings:</p>
<pre><code class="bash">$ jt [ foo + bar % ] baz % <<EOT
- {"foo":"{\"bar\":100}","baz":200}
- {"foo":"{\"bar\":200}","baz":300}
- {"foo":"{\"bar\":300}","baz":400}
- EOT
100 200
200 300
300 400
</code></pre>
<p><strong>Note:</strong> The <code>+</code> command does not modify the original JSON:</p>
<pre><code class="bash">$ jt [ foo + bar % ] % <<EOT
- {"foo":"{\"bar\":100}","baz":200}
- {"foo":"{\"bar\":200}","baz":300}
- {"foo":"{\"bar\":300}","baz":400}
- EOT
100 {"foo":"{\"bar\":100}","baz":200}
200 {"foo":"{\"bar\":200}","baz":300}
300 {"foo":"{\"bar\":300}","baz":400}
</code></pre>
<h3 id="Column-Headings">Column Headings</h3>
<p>The <code>%=</code><var>NAME</var> and <code>^=</code><var>NAME</var> commands are like <code>%</code> and <code>^</code> above, but they
also assign column headings, which are printed as the first line of output:</p>
<pre><code class="bash">$ jt [ foo %=Foo ] bar ^=Bar baz %=Baz <<EOT
- {
- "foo": 100,
- "bar": [
- {"baz": 200},
- {"baz": 300},
- {"baz": 400}
- ]
- }
- EOT
Foo Bar Baz
100 0 200
100 1 300
100 2 400
</code></pre>
<p><strong>Note:</strong> The heading <var>NAME</var> must be a JSON escaped string (eg. to have a
column heading with embedded tab characters use <code>%=foo\tbar</code> instead of
<code>"%=foo bar"</code>).</p>
<h3 id="Joins">Joins</h3>
<p>Notice the empty column — some objects don't have the <var>bar</var> key:</p>
<pre><code class="bash">$ jt [ foo % ] bar % <<EOT
- {"foo":100,"bar":1000}
- {"foo":200}
- {"foo":300,"bar":3000}
- EOT
100 1000
200
300 3000
</code></pre>
<p>Enable inner join mode with the <code>-j</code> flag. This removes output rows when a key
in the traversal path doesn't exist:</p>
<pre><code class="bash">$ jt -j [ foo % ] bar % <<EOT
- {"foo":100,"bar":1000}
- {"foo":200}
- {"foo":300,"bar":3000}
- EOT
100 1000
300 3000
</code></pre>
<p>Note that this does not remove rows when the key exists and the value is empty:</p>
<pre><code class="bash">$ jt -j [ foo % ] bar % <<EOT
- {"foo":100,"bar":1000}
- {"foo":200,"bar":""}
- {"foo":300,"bar":3000}
- EOT
100 1000
200
300 3000
</code></pre>
<h3 id="Explicit-Iteration">Explicit Iteration</h3>
<p>Sometimes the implicit iteration over arrays is awkward:</p>
<pre><code class="bash">$ jt . ^ . ^ % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
0 bar 100
1 bar 200
</code></pre>
<p>Should the first <code>^</code> be printing the array index of the implicit iteration
(which it does, in this case) or the object key (i.e. <var>foo</var>) of the explicit
iteration of the <code>.</code> command?</p>
<p>Another awkward case is printing arrays:</p>
<pre><code class="bash">$ jt foo % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
{"bar":100}
{"bar":200}
</code></pre>
<p>The array can not be printed with the <code>%</code> command because it is being iterated
over implicitly. Instead, the items in the array are printed, which may not be
the desired behavior.</p>
<p>The <code>-a</code> flag eliminates the ambiguity by enabling explicit iteration. In this
mode the <code>.</code> command must be used to iterate over both objects and arrays —
arrays are not automatically iterated over.</p>
<p>Now the array can be printed:</p>
<pre><code class="bash">$ jt -a foo % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
[{"bar":100},{"bar":200}]
</code></pre>
<p>Or the first <code>^</code> can print the array index, as before:</p>
<pre><code class="bash">$ jt -a . . ^ . ^ % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
0 bar 100
1 bar 200
</code></pre>
<p>Or it can print the object key:</p>
<pre><code class="bash">$ jt -a . ^ . . ^ % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
foo bar 100
foo bar 200
</code></pre>
<p>Or, with the addition of one more <code>^</code> command, it can print both:</p>
<pre><code class="bash">$ jt -a . ^ . ^ . ^ % <<EOT
- {
- "foo": [
- {"bar":100},
- {"bar":200}
- ]
- }
- EOT
foo 0 bar 100
foo 1 bar 200
</code></pre>
<h2 id="SEE-ALSO">SEE ALSO</h2>
<p><strong>Jt</strong> is based on ideas from the excellent <strong>jshon</strong> tool, which can be found
at <a href="http://kmkeen.com/jshon/" data-bare-link="true">http://kmkeen.com/jshon/</a>. Source code for <strong>jt</strong> is available at
<a href="https://github.com/micha/json-table" data-bare-link="true">https://github.com/micha/json-table</a>.</p>
<h2 id="BUGS">BUGS</h2>
<p>Please open an issue here: <a href="https://github.com/micha/json-table/issues" data-bare-link="true">https://github.com/micha/json-table/issues</a>.</p>
<h2 id="COPYRIGHT">COPYRIGHT</h2>
<p>Copyright © 2017 Micha Niskin <code><[email protected]></code>, distributed under
the Eclipse Public License, version 1.0. This is free software: you are free
to change and redistribute it. There is NO WARRANTY, to the extent permitted
by law.</p>
<ol class='man-decor man-foot man foot'>
<li class='tl'></li>
<li class='tc'>July 2017</li>
<li class='tr'>jt(1)</li>
</ol>
</div>
</body>
</html>