.Dd $Mdocdate: March 12 2023 $
.Dt JSON 1
.Os Telodendria Project
.Sh NAME
.Nm json
.Nd A simple command line utility for parsing and generating JSON.
.Sh SYNOPSIS
.Nm
.Op Fl s Ar query
.Op Fl e Ar str
.Sh DESCRIPTION
.Nm
is a simple command line utility for dealing with JSON. It is
somewhat inspired by
.Xr jq 1 ,
but is not compatible in any way with it.
.Nm
is designed to be much simpler than
.Xr jq 1 ,
and is built on Telodendria's own
.Xr Json 3
API. It primarily exists to ease development of Telodendria, and
to make development possible without having to install any external
tools.
.Pp
The options are as follows. Unless stated otherwise, these options
are mutually exclusive, and the last one specified takes precedence.
All positional parameters are ignored.
.Bl -tag -width Ds
.It Fl s Ar query
Use
.Va query
to query a field from a JSON object given on the standard input.
The query syntax very vaguely resembles C code, but it is much
more primitive. Multiple queries are separated by an arrow
(``->''). This makes it trivial to drill down into nested
objects and arrays.
.Pp
To select a value from an object, just specify the key. To select
an element from an array specify the key whose value is the array,
and then use the C square bracket syntax to select an element.
.Pp
A number of ``functions'' exist to make
.Nm
more versatile. Functions are called by prefacing the key with
a ``@'' symbol. Functions can appear anywhere in the query, provided
they make sense within the context of the JSON object being processed.
The available functions are as follows:
.Bl -tag -width Ds
.It keys
When applied to an object, outputs an array of keys.
.It length
When applied to an array, outputs the number of elements in the
array. When applied to a string, returns the number of bytes
needed to store the decoded version of the string.
.It decode
When applied to a string, outputs the decoded version of the
string.
.El
.Pp
When a key is prefaced with the ``^'' symbol, then instead of getting
the value at that key, it is removed from the object, and the new
object is passed along. 
.It Fl e Ar str
Encode
.Va str
as a JSON string and print it to standard output. This is useful for
generating JSON with shell scripts.
.El
.Pp
If no options are specified, then the default behavior of
.Nm
is to read a JSON object given on the standard input and pretty-print
it to the standard output, or print an error to standard error if
the given input is invalid.
.Sh EXAMPLES
.Pp
Get the error string of an error returned by a Matrix API endpoint:
.Bd -literal -offset indent
json -s 'error->@decode'
.Ed
.Pp
Get the number of stages in the first flow listed in a list
of user-interactive authentication flows:
.Bd -literal -offset indent
json -s 'flows[0]->stages->@length'
.Ed
.Pp
Get the first stage of the first flow listed in a list
of user-interactive authentication flows:
.Bd -literal -offset indent
json -s 'flows[0]->stages[0]->@decode'
.Ed
.Pp
List the keys in a JSON object:
.Bd -literal -offset indent
json -s '@keys'
.Ed
.Pp
Get the number of keys in a JSON object:
.Bd -literal -offset indent
json -s '@keys->@length'
.Ed
.Sh EXIT STATUS
.Nm
exits with
.Va EXIT_SUCCESS
if all command line options were valid and the given JSON object
parses successfully. It exits with
.Va EXIT_FAILURE
in all other scenarios.