jo
JO(1) JO(1)
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 val-
ues 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 substi-
tute the result
Escape the special character with a backslash to prevent this interpre-
tation.
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 stan-
dard 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":""quot- "a":8 "a":true "a":""quot-
ed"" ed""
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 be-
comes 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 charac-
ter of value is an open brace or a bracket we attempt to decode the re-
mainder 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 bool-
ean 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 re-
sults. If you quote a numeric value, jo will make it a string. Com-
pare 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 mes-
sage to print, but the output contains garbage anyway. This was de-
signed thusly.
RETURN CODES
jo exits with a code 0 on success and non-zero on failure after indi-
cating what caused the failure.
AVAILABILITY
<http://github.com/jpmens/jo>
CREDITS
o This program uses json.[ch], by Joseph A. Adams.
SEE ALSO
o <https://stedolan.github.io/jq/>
o <https://github.com/micha/jsawk>
o <https://github.com/jtopjian/jsed>
o strtod(3)
AUTHOR
Jan-Piet Mens <http://jpmens.net>
User Manuals JO(1)
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