Month: August 2021

Use Crontab for automating recurring tasks on Fedora/CentOS

04/08/2021 Nicolas Baptista Fedora/CentOS/RedHat, Server Maintenance 0 Comments

You can use a tool that is called “Crontab” for recurring tasks automation. It is available for all the Linux systems and still the most used solution.

Edit the crontab configuration file

crontab -e

This will open vi, the default linux editor, that will allow you to edit the recurring tasks for a specific date and time. 

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  *  user command to be executed

In vi the main commands used are:
– The escape key (:x! to save OR :q! to quit)
– a to append text
– i to insert text
– dd to remove the line
– x to delete the current selected character

Verify the date and time zone

You can verify the date and the time zone (most of the cloud machines are using the UTC time zone). you can use the following command “date”:

# date
Wed Aug  4 01:10:10 UTC 2021

Sort your result by distance – Node.JS

01/08/2021 Nicolas Baptista Javascript, JSON, Node.JS, REST API 0 Comments

Supposed that you return in your Node.JS backend a list of items, and you want to sort the results by distance.

For exemple, you do a GET /usersLocation and you have it:

[
   {
      name: "Paul",
      gender: "man",
      distance: 4.1
   },
   {
      name: "Philip",
      gender: "man",
      distance: 4.9
   },
   {
      name: "Elina",
      gender: "woman",
      distance: 2.5
   }
]

In your app you have the result to be listed by distance for exemple, so the user can know who is nearest first, and don’t have to scroll down to see that Elina is nearest. To do so, we can add this portion of code before returning the list of items:

    // items : variable containing all the items

    // SORT
    for(let a=items.length;a>0;a--)
    {
       for(let b=0;b<a-1;b++)
       {
          if(items[b].distance>items[b+1].distance) // we order by distance
          {
             // we swap the items
             tmp = items[b];
             items[b]=items[b+1];
             items[b+1]=tmp;
          }
       }
    }

    // returning the response for AWS Lambda
    const response = {
        statusCode: 200,
        body: JSON.stringify(items),
    };
    return response;
};

New response:

[
   {
      name: "Elina",
      gender: "woman",
      distance: 2.5
   },
   {
      name: "Paul",
      gender: "man",
      distance: 4.1
   },
   {
      name: "Philip",
      gender: "man",
      distance: 4.9
   }
]

Nicolas BAPTISTA