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JSON is used by both web services and command line tools, so a modern Unix shell needs support for it.
This page describes Oil's JSON support as of December 2019 (version 0.7.pre8). It will likely expand over time, depending on user feedback.
(Note: the help
builtin will provide shorter, reference-style documentation.)
The json
builtin has read
and write
subcommands, which convert
between text and data structures in memory. Oil's data structures are like
those in Python and JavaScript, so this correspondence is natural.
json read
parses from stdin
Usage:
json read FLAGS* VAR_NAME
Flags:
None for now, but there likely will be one to skip UTF-8 validation.
Examples:
$ cat stats.json
{"count": 42}
# Read from a file. myvar is created in local scope.
$ json read :myvar < stats.json
# Use = to pretty print an expression
$ = myvar
(Dict) {'count': 42}
# 'json read' is valid at the end of a pipeline (because Oil 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
Notes:
:
.json read
is consistent with shell's read
builtin, which reads a line
from a file and splits it.json write
prints to stdout
Usage:
json write FLAGS* VAR_NAME+
Flags:
-indent=2 Indentation size
-pretty=true Whether to add newlines for readability
Examples:
# Create a Dict. As in JavaScript, keys don't require quotes.
$ var d = {name: "bob", age: 42}
# Print the Dict as JSON. By default, newlines are added for readability, with
# 2 space indentation.
$ json write :d
{
"name": "bob",
"count": 42
}
$ json write -indent 4 :d
{
"name": "bob",
"count": 42
}
$ json write -pretty=F :d
{"name": "bob", "count": 42}
Notes:
-indent
is ignored if -pretty
is false.json
builtin is part of the Oil language, so it uses Oil's flag
syntax, which is based on Go's. In particular, boolean flags are written
-pretty=F
rather than -pretty F
, but you can write -indent=4
or
-indent 4
.Oil 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"
}
Under the hood, Oil uses yajl and a fork of the py-yajl binding.