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JSON in Oils

JSON is used by both web services and command line tools, so a modern Unix shell needs to support it.

Oils has a json builtin which you can use from bot OSH and YSH.

It also has a parallel json8 builtin with the same uage. See J8 Notation for details on the encoding.

The json builtin has read and write subcommands, which convert between serialized data languages and in-memory data structures.

YSH data structures are like those in Python and JavaScript, so this correspondence is natural.

json read parses from stdin

Usage:

json  read (PLACE?)
json8 read (PLACE?)

Examples:

$ cat stats.json
{"count": 42}

# Read from a file.  By default, the variable _reply is written.
$ json read < stats.json

# Use = to pretty print an expression
$ = _reply
(Dict)   {'count': 42}

Specify a place to put the data:

$ json read (&myvar) < stats.json

$ = myvar
(Dict)   {'count': 42}

Use it in a pipeline:

# 'json read' is valid at the end of a pipeline (because YSH implements
# shopt -s lastpipe)
$ echo '{"count": 42}' | json read (&myvar)

Failure with invalid input data:

$ echo '[ "incomplete"' | json read (&myvar) < invalid.json
[ "incomplete"
 ^
json read: premature EOF

$ echo $?
1

json write prints to stdout

Usage:

json write (EXPR, space=2)

EXPR is an expression that evaluates to a serializable object.

space is the number of spaces that object and array entries are indented
by.  If it's 0 or less, then no newlines or spaces are printed.

Examples:

$ var d = {name: "bob", age: 42}  # create Dict

$ json write (d)  # print as JSON, with 2 space indent
{
  "name": "bob",
  "count": 42
}

$ json write (d, space=0)  # no indent at all
{"name":"bob","count":42}

write builtin

TODO

write --j8 hello there
write --json hello there  # unicode replacement char

Filter Data Structures with YSH Expressions

Once your data is deserialized, you can use YSH expression to operate on it.

$ echo '{"counts": [42, 99]}' | json read (&d)

$ = d['counts']
(List)   [42, 99]

$ = d['counts'][1]
(Int)    99

# d->counts is a synonym for d["counts"]
$ json write (d->counts)
[
  42,
  99
]

Note: It may more efficient to filter large data structures with tools like jq first.

Other Data Structures Can Be Printed as JSON

YSH arrays and shell arrays both serialize to a list of strings:

$ declare sharray=( foo.txt *.py )
$ json write (sharray)
[  
   "foo.txt",
   "one.py",
   "two.py"
]

$ var oilarray = :| foo.txt *.py |
$ json write (oilarray)
[  
   "foo.txt",
   "one.py",
   "two.py"
]

Bash-style associative arrays are printed like Dict[Str, Str]:

$ declare -A assoc=(["key"]=value)
$ json write (assoc)
{
  "key": "value"
}