% JO(1) User Manuals

# NAME

jo - JSON output from a shell

# SYNOPSIS

jo [-p] [-a] [-B] [-e] [-v] [-V] [-d keydelim] [--] [ [-s|-n|-b] word ...]

# DESCRIPTION

*jo* creates a JSON string on _stdout_ from _word_s given it as arguments or read from _stdin_. Without
option `-a` it generates an object whereby each _word_ is a `key=value` (or `key@value`)
pair with _key_ being the JSON object element and _value_ its value. *jo* attempts to
guess the type of _value_ in order to create number (using _strtod(3)_), string, or null values in JSON.

*jo* normally treats _key_ as a literal string value. If the `-d` option is specified, _key_ will be
interpreted as an _object path_, whose individual components are separated by the first character of _keydelim_.

*jo* normally treats _value_ as a literal string value, unless it begins with one of the following characters:

value action
----- ------
@file substitute the contents of _file_ as-is
%file substitute the contents of _file_ in base64-encoded form
:file interpret the contents of _file_ as JSON, and substitute the result

Escape the special character with a backslash to prevent this interpretation.

*jo* treats `key@value` specifically as boolean JSON elements: if the value begins with `T`, `t`,
or the numeric value is greater than zero, the result is `true`, else `false`. A missing or
empty value behind the colon results in a `null` JSON element.

*jo* creates an array instead of an object when `-a` is specified.

When the `:=` operator is used in a _word_, the name to the right of `:=` is a file containing JSON which is parsed and assigned to the key left of the operator. The file may be specified as `-` to read from _jo_'s standard input.


# TYPE COERCION

*jo*'s type guesses can be overridden on a per-word basis by prefixing _word_ with `-s` for _string_,
`-n` for _number_, or `-b` for _boolean_. The list of _word_s *must* be prefixed with `--`, to indicate
to *jo* that there are no more global options.

Type coercion works as follows:

word         -s               -n           -b        default
------------ ---------------- ------------ --------- ----------------
a=           "a":""           "a":0        "a":false "a":null
a=string     "a":"string"     "a":6        "a":true  "a":"string"
a=\"quoted\" "a":"\"quoted\"" "a":8        "a":true  "a":"\"quoted\""
a=12345      "a":"12345"      "a":12345    "a":true  "a":12345
a=true       "a":"true"       "a":1        "a":true  "a":true
a=false      "a":"false"      "a":0        "a":false "a":false
a=null       "a":""           "a":0        "a":false "a":null

Coercing a non-number string to number outputs the _length_ of the string.

Coercing a non-boolean string to boolean outputs `false` if the string is empty, `true` otherwise.

Type coercion only applies to `key=value` words, and individual words in a `-a` array.
Coercing other words has no effect.

# EXAMPLES

Create an object. Note how the incorrectly-formatted float value becomes a string:

	$ jo tst=1457081292 lat=12.3456 cc=FR badfloat=3.14159.26 name="JP Mens" nada= coffee@T
	{"tst":1457081292,"lat":12.3456,"cc":"FR","badfloat":"3.14159.26","name":"JP Mens","nada":null,"coffee":true}

Pretty-print an array with a list of files in the current directory:

	$ jo -p -a *
	[
	 "Makefile",
	 "README.md",
	 "jo.1",
	 "jo.c",
	 "jo.pandoc",
	 "json.c",
	 "json.h"
	]

Create objects within objects; this works because if the first character of value is an open brace or a bracket we attempt to decode the remainder as JSON. Beware spaces in strings ...

	$ jo -p name=JP object=$(jo fruit=Orange hungry@0 point=$(jo x=10 y=20 list=$(jo -a 1 2 3 4 5)) number=17) sunday@0
	{
	 "name": "JP",
	 "object": {
	  "fruit": "Orange",
	  "hungry": false,
	  "point": {
	   "x": 10,
	   "y": 20,
	   "list": [
	    1,
	    2,
	    3,
	    4,
	    5
	   ]
	  },
	  "number": 17
	 },
	 "sunday": false
	}

Booleans as strings or as boolean (pay particular attention to _switch_; the `-B` option disables the default detection of the "`true`", "`false`", and "`null`" strings):

	$ jo switch=true morning@0
	{"switch":true,"morning":false}

	$ jo -B switch=true morning@0
	{"switch":"true","morning":false}

Elements (objects and arrays) can be nested. The following example nests an array called _point_ and an object named _geo_:

	$ jo -p name=Jane point[]=1 point[]=2 geo[lat]=10 geo[lon]=20
	{
	   "name": "Jane",
	   "point": [
	      1,
	      2
	   ],
	   "geo": {
	      "lat": 10,
	      "lon": 20
	   }
	}

The same example, using object paths:

	$ jo -p -d. name=Jane point[]=1 point[]=2 geo.lat=10 geo.lon=20
	{
	   "name": "Jane",
	   "point": [
	      1,
	      2
	   ],
	   "geo": {
	      "lat": 10,
	      "lon": 20
	   }
	}

Without `-d`, a different object is generated:

	$ jo -p name=Jane point[]=1 point[]=2 geo.lat=10 geo.lon=20
	{
	   "name": "Jane",
	   "point": [
	      1,
	      2
	   ],
	   "geo.lat": 10,
	   "geo.lon": 20
	}

Create empty objects or arrays, intentionally or potentially:

	$ jo < /dev/null
	{}

	$ MY_ARRAY=(a=1 b=2)
	$ jo -a "${MY_ARRAY[@]}" < /dev/null
	["a=1","b=2"]


Type coercion:

	$ jo -p -- -s a=true b=true -s c=123 d=123 -b e="1" -b f="true" -n g="This is a test" -b h="This is a test"
	{
	   "a": "true",
	   "b": true,
	   "c": "123",
	   "d": 123,
	   "e": true,
	   "f": true,
	   "g": 14,
	   "h": true
	}

	$ jo -a -- -s 123 -n "This is a test" -b C_Rocks 456
	["123",14,true,456]

Read element values from files: a value which starts with `@` is read in plain whereas if it begins with a `%` it will be base64-encoded and if it starts with `:` the contents are interpreted as JSON:

	$ jo program=jo authors=@AUTHORS
	{"program":"jo","authors":"Jan-Piet Mens <jpmens@gmail.com>"}

	$ jo filename=AUTHORS content=%AUTHORS
	{"filename":"AUTHORS","content":"SmFuLVBpZXQgTWVucyA8anBtZW5zQGdtYWlsLmNvbT4K"}

	$ jo nested=:nested.json
	{"nested":{"field1":123,"field2":"abc"}}

These characters can be escaped to avoid interpretation:

	$ jo name="JP Mens" twitter='\@jpmens'
	{"name":"JP Mens","twitter":"@jpmens"}

	$ jo char=" " URIescape=\\%20
	{"char":" ","URIescape":"%20"}

	$ jo action="split window" vimcmd="\:split"
	{"action":"split window","vimcmd":":split"}

Read element values from a file in order to overcome ARG_MAX limits during object assignment:

	$ ls | jo -a > child.json
	$ jo files:=child.json
	{"files":["AUTHORS","COPYING","ChangeLog" ....

	$ ls *.c | jo -a > source.json; ls *.h | jo -a > headers.json
	$ jo -a :source.json :headers.json
	[["base64.c","jo.c","json.c"],["base64.h","json.h"]]

# OPTIONS

*jo* understands the following global options. 

-a
:   Interpret the list of _words_ as array values and produce an array instead of
    an object.

-B
:   By default *jo* interprets the strings "`true`" and "`false`" as boolean elements
    `true` and `false` respectively, and "`null`" as `null`. Disable with this option.

-e
:   Ignore empty stdin (i.e. don't produce a diagnostic error when *stdin*
    is empty)

-p
:   Pretty-print the JSON string on output instead of the terse one-line output it
    prints by default.

-v
:   Show version and exit.

-V
:   Show version as a JSON object and exit.

# BUGS

Probably.

If a value given to *jo* expands to empty in the shell, then *jo* produces a `null` in object mode, and might appear to hang in array mode; it is not hanging, rather it's reading _stdin_. This is not a bug.

Numeric values are converted to numbers which can produce undesired results. If you quote a numeric value, *jo* will make it a string. Compare the following:

	$ jo a=1.0
	{"a":1}
	$ jo a=\"1.0\"
	{"a":"1.0"}

Omitting a closing bracket on a nested element causes a diagnostic message to print, but the output contains garbage anyway. This was designed thusly.

# RETURN CODES

*jo* exits with a code 0 on success and non-zero on failure after indicating what
caused the failure.

# AVAILABILITY

<http://github.com/jpmens/jo>

# CREDITS

* This program uses `json.[ch]`, by Joseph A. Adams.

# SEE ALSO

* <https://stedolan.github.io/jq/>
* <https://github.com/micha/jsawk>
* <https://github.com/jtopjian/jsed>
* strtod(3)

# AUTHOR

Jan-Piet Mens <http://jpmens.net>