Loop through JSON file in bash script

Question

I have a bash script that user enter name of a database and then my script needs to loop through this database config file. my JSON looks like this:

{
    "_id":1,
    "db_name":"postgres",
    "username":"postgres_user",
    "password":"postgres_pass",
    "daily" : {
               "days_to_backup" : [1,2],
               "delete_after" : 14,
               "compressed" : true,
           "path" : "localhost"
         },
    "monthly" : {
               "days_to_backup" : [2,5,30],
               "delete_after" : 7,
               "compressed" : false,
           "path" :" localhost"
         },
    "yearly" : {
               "days_to_backup" : [100],
               "delete_after" : 14,
               "compressed" : true,
           "path" : "localhost"
          }
}
{
    "_id":2,
    "db_name":"test",
    "username":"test_user",
    "password":"test_pass",
    "daily" : {
               "days_to_backup" : [1,7],
               "delete_after" : 14,
               "compressed" : true,
           "path" : "localhost"
           },

    "monthly" : {
               "days_to_backup" : [2,5,25],
               "delete_after" : 7,
               "compressed" : false,
           "path" : "localhost"
           },

    "yearly" : {
               "days_to_backup" : [50],
               "delete_after" : 14,
               "compressed" : true,
           "path" : "localhost"
           }


}

Now once user run the script with particular database name, i want to loop through the "days_to_backup" numbers and for each day look it it's equal for today date. The problem is that i don't know how to fetch the daily/monthly/yealy.days_to_backup and then loop through the days. I tried with jq :

#! /bin/sh

#monday is first day of the week
export Today=$(date +%d)
while getopts d: flag
do
    case "${flag}" in
        d) database=${OPTARG};;


    esac
done

if jq .db_name file.json | grep $database
then
        jq 'select(.db_name=="'$database'")' file.json
        ##this one returns the whole document of the specified database
        ##loop here for daily/monthly_yearly.days_to_backup???
else
        echo "database not found"
fi

Edit: my input is the name of the database ( " postgres " ) and then i will iterate through the daily/monthly/yearly array and if the number is like current date ( today is 8 of the month) so the output will be - echo "backup today".

Edit2: sorry my bad. for daily it means that day of the week so (1,7) are sunday and saturday and if current date is sunday or saturday i want and echo "backup today". for monthly it means the day of the month, so if i have monthly (01,08) it will echo "backup today" because today is the 8th of the month. and for yearly i want days since the first day of the year.

Ok so I succeeded to loop through the array but the problem now is that it run over the array of the 2 big objects (id 1 + 2)

for i in $(jq -r ".daily.days_to_backup | .[]" file.json)
  do
    echo $i "im number"
  done

how do I select that it will run only over _id:1 / db_name: postgres?

Please add to your question example input and your desired output (no description). — Cyrus
– Cyrus, Commented Nov 8, 2020 at 15:24
Does this mean that on the 29th of each month you're supposed to do a daily backup and a yearly backup, and on the 30th you're supposed to do a monthly backup? — glenn jackman
– glenn jackman, Commented Nov 8, 2020 at 15:29
edited. when I call the script i specify with -d the name of the database and then for each daily/monthly/yearly.days_to_Backup array i want to check if the number there is same as current date. if yes just print a echo that it's same date. — dddd4
– dddd4, Commented Nov 8, 2020 at 15:30
You have to be a bit careful with date +%d -- for single digit days, you get a leading zero, which might throw off your comparisons. — glenn jackman
– glenn jackman, Commented Nov 8, 2020 at 15:31

peak · Accepted Answer · 2020-11-09 04:02:36Z

3

An efficient approach would be based on using any, e.g. along the lines of the following:

jq --arg db $database --argjson Today $Today '
    select(.db_name==$db and
           any(.daily[], .monthly[], .yearly[]; . == $Today) ) 
' file.json

Note that both parameters ($database and $Today) should be passed in as command-line arguments rather than provided using shell-based string interpolation. Using --argjson will ensure that any leading 0s in the shell variable $Today do not cause problems.

Note also that the above query will return a stream of 0 or more values. You might want to guarantee the names are distinct, e.g. by using the jq built-in filter unique (defined for arrays), or the stream-oriented filter uniques defined in the jq Cookbook.

edited Nov 9, 2020 at 4:02

answered Nov 8, 2020 at 17:00

peak

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4 Comments

Philippe Over a year ago

Could you please explain how . can be equal to $Today which is a number ?

peak Over a year ago

Using --argjson will in this case ensure Today is a JSON number.

Philippe Over a year ago

But . is a whole struecture.

peak Over a year ago

Nope. Look at the definition of any/2 in builtin.jq

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