JSON to fixed width file - json

Question

I have to extract data from JSON file depending on a specific key. The data then has to be filtered (based on the key value) and separated into different fixed width flat files. I have to develop a solution using shell scripting.
Since the data is just key:value pair I can extract them by processing each line in the JSON file, checking the type and writing the values to the corresponding fixed-width file.
My problem is that the input JSON file is approximately 5GB in size. My method is very basic and would like to know if there is a better way to achieve this using shell scripting ?
Sample JSON file would look like as below:
{"Type":"Mail","id":"101","Subject":"How are you ?","Attachment":"true"}
{"Type":"Chat","id":"12ABD","Mode:Online"}
The above is a sample of the kind of data I need to process.

Answer 1

Give this a try:
#!/usr/bin/awk
{
line = ""
gsub("[{}\x22]", "", $0)
f=split($0, a, "[:,]")
for (i=1;i<=f;i++)
if (a[i] == "Type")
file = a[++i]
else
line = line sprintf("%-15s",a[i])
print line > file ".fixed.out"
}
I made assumptions based on the sample data provided. There is a lot based on those assumptions that may need to be changed if the data varies much from what you've shown. In particular, this script will not work properly if the data values or field names contain colons, commas, quotes or braces. If this is a problem, it's one of the primary reasons that a proper JSON parser should be used. If it were my assignment, I'd push back hard on this point to get permission to use the proper tools.
This outputs lines that have type "Mail" to a file named "Mail.fixed.out" and type "Chat" to "Chat.fixed.out", etc.
The "Type" field name and field value ("Mail", etc.) are not output as part of the contents. This can be changed.
Otherwise, both the field names and values are output. This can be changed.
The field widths are all fixed at 15 characters, padded with spaces, with no delimiters. The field width can be changed, etc.
Let me know how close this comes to what you're looking for and I can make some adjustments.

Answer 2

perl script
#!/usr/bin/perl -w
use strict;
use warnings;
no strict 'refs'; # for FileCache
use FileCache; # avoid exceeding system's maximum number of file descriptors
use JSON;
my $type;
my $json = JSON->new->utf8(1); #NOTE: expect utf-8 strings
while(my $line = <>) { # for each input line
# extract type
eval { $type = $json->decode($line)->{Type} };
$type = 'json_decode_error' if $#;
$type ||= 'missing_type';
# print to the appropriate file
my $fh = cacheout '>>', "$type.out";
print $fh $line; #NOTE: use cache if there are too many hdd seeks
}
corresponding shell script
#!/bin/bash
#NOTE: bash is used to create non-ascii filenames correctly
__extract_type()
{
perl -MJSON -e 'print from_json(shift)->{Type}' "$1"
}
__process_input()
{
local IFS=$'\n'
while read line; do # for each input line
# extract type
local type="$(__extract_type "$line" 2>/dev/null ||
echo json_decode_error)"
[ -z "$type" ] && local type=missing_type
# print to the appropriate file
echo "$line" >> "$type.out"
done
}
__process_input
Example:
$ ./script-name < input_file
$ ls -1 *.out
json_decode_error.out
Mail.out