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jo - JSON output from a shell
Contents
Availability
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 val‐
ue, 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 con‐
tains garbage anyway. This was designed thusly.
Credits
• This program uses json.[ch], by Joseph A. Adams.
Description
jo creates a JSON string on stdout from words given it as arguments or read from stdin. If -f is speci‐
fied, jo first loads the contents of file as a JSON object or array, then modifies it with subsequent
words before printing the final JSON string to stdout. file may be specified as - to read from jo’s
standard input; this takes precedence over reading words 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.
A missing or empty value normally results in an element whose value is null. If -n is specified, this
element is not created.
jo normally treats key as a literal string value. If the -d option is specified, key will be interpreted
as an objectpath, 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 charac‐
ters:
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.
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.
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"]]
Add elements to existing JSON:
$ jo -f source.json 1 | jo -f - 2 3
["base64.c","jo.c","json.c",1,2,3]
$ curl -s 'https://noembed.com/embed?url=https://www.youtube.com/watch?v=dQw4w9WgXcQ' | jo -f - status=Rickrolled
{ ...., "type":"video","author_url":"https://www.youtube.com/user/RickAstleyVEVO","status":"Rickrolled"}
Deduplicate object keys (jo appends duplicate object keys by default):
$ jo a=1 b=2 a=3
{"a":1,"b":2,"a":3}
$ jo -D a=1 b=2 a=3
{"a":3,"b":2}
Name
jo - JSON output from a shell
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 re‐
spectively, and “null” as null. Disable with this option.
-D Deduplicate object keys.
-e Ignore empty stdin (i.e. don’t produce a diagnostic error when stdin is empty)
-n Do not add keys with empty values.
-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.
Return Codes
jo exits with a code 0 on success and non-zero on failure after indicating what caused the failure.
See Also
• <https://stedolan.github.io/jq/>
• <https://github.com/micha/jsawk>
• <https://github.com/jtopjian/jsed>
• strtod(3)
Synopsis
jo [-p] [-a] [-B] [-D] [-e] [-n] [-v] [-V] [-d keydelim] [-f file] [–] [ [-s|-n|-b] word ...]
Type Coercion
jo’s type guesses can be overridden on a per-word basis by prefixing word with -s for string, -n for num‐ber, or -b for boolean. The list of words 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.
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