I am trying to create my own low-level discovery rule using JSON format which is described on:
http://www.zabbix.com/documentation/2.0/manual/discovery/low_level_discovery#discovery_item_json_format

1. zabbix_agentd host (h157)

a) file /usr/local/home/a (exact from documentation content):

#!/usr/bin/perl

$first = 1;

print "{\n";
print "\t\"vfs.fs.discovery_perl\":[\n\n";

for (`cat /proc/mounts`)
{
($fsname, $fstype) = m/\S+ (\S+) (\S+)/;
$fsname =~ s!/!
/!g;

print "\t,\n" if not $first;
$first = 0;

print "\t{\n";
print "\t\t\"

{#FSNAME}\":\"$fsname\",\n";
print "\t\t\"{#FSTYPE}\":\"$fstype\"\n";
print "\t}\n";
}

print "\n\t]\n";
print "}\n";

b) zabbix_agentd.conf:

UserParameter=a,/usr/local/home/a


2. zabbix_server side:

a) testing item 'a':

# zabbix_get -s h157 -k a
{
"vfs.fs.discovery_perl":[

{
"{#FSNAME}

":"\/",
"

{#FSTYPE}":"rootfs"
}
,
{
"{#FSNAME}":"\/",
"{#FSTYPE}

":"ext4"
}
,
{
"

{#FSNAME}":"\/dev",
"{#FSTYPE}":"devtmpfs"
}
,
{
"{#FSNAME}

":"\/proc",
"

{#FSTYPE}":"proc"
}
,
{
"{#FSNAME}":"\/sys",
"{#FSTYPE}

":"sysfs"
}
,
{
"

{#FSNAME}":"\/run",
"{#FSTYPE}":"tmpfs"
}
,
{
"{#FSNAME}

":"\/dev\/pts",
"

{#FSTYPE}":"devpts"
}
,
{
"{#FSNAME}":"\/dev\/shm",
"{#FSTYPE}

":"tmpfs"
}
,
{
"

{#FSNAME}":"\/dist",
"{#FSTYPE}":"ext4"
}
,
{
"{#FSNAME}

":"\/dist\/dev",
"

{#FSTYPE}":"ext4"
}
,
{
"{#FSNAME}":"\/dist\/usr\/run",
"{#FSTYPE}

":"ext4"
}
,
{
"

{#FSNAME}":"\/matrix\/dev\/cgroup",
"{#FSTYPE}":"cgroup"
}
,
{
"{#FSNAME}

":"\/fs\/m-b10",
"

{#FSTYPE}":"ext4"
}
,
{
"{#FSNAME}":"\/fs\/data2",
"{#FSTYPE}

":"ext4"
}
,
{
"

{#FSNAME}

":"\/fs\/data",
"

{#FSTYPE}

":"ext4"
}

]
}

Data returned from item 'a' seems to be correct JSON format.

However in position with discovery rule 'a' there is an error:
"wrong data in JSON object"