Use “dG” command, if you want to delete all lines in a file starting from the line under the cursor in vi.
Additional commands to delete lines
One can leverage the explosion of generative AI art engines to create your own clip art.
Here’s a clipart that I created using the prompt “moscow mule drink illustration, clipart”
A simple and useful visual of joins in SQL by Taylor Brownlow from this post https://towardsdatascience.com/take-your-sql-from-good-to-great-part-3-687d797d1ede
A self note for querying json data in SQLite. BTW, I think SQLite is an under utilized and under appreciated swiss army tool for data storage and manipulation. And thanks to Richard Hipp, it is free.
If you have a column defined as a json type in your SQLite database, quickest way to search for the data is json_extract. A full set of functions available are documented at https://www.sqlite.org/json1.html
If you have a column named family_details in a table family with the following json in it as an example
{
"father": {
"name": "dad",
"birthday": "1/1/2000",
"pet_name": "daddy"
},
"mother": {
"name": "mom",
"birthday": "1/1/2001",
"pet_name": "mommy"
},
"sons": [
{
"name": "son_one",
"birthday": "1/2/2020",
"pet_name": "sonny_one"
},
{
"name": "son_two",
"birthday": "1/2/2021",
"pet_name": "sonny_two"
}
],
"daughters": [
{
"name": "princess_one",
"birthday": "1/2/2020",
"pet_name": "princy_one"
},
{
"name": "princess_two",
"birthday": "1/2/2021",
"pet_name": "princy_two"
}
]
}and you want to print the name of the father, you can use
select json_extract(family_details, '$.father.name') as father_name
from family
json_extract uses the name of the column and the json node as parameters. In this case, we used $(which denotes the root), father and name (under father) as the json node.
That was a pretty long title for the post :). I love nginx for it’s flexibility and ease of use. It is like a swiss army knife.. can do a lot of things :).
We needed to serve some dynamic content for one of our use cases. If user visits a site using the following URL format http://example.com/23456789/678543 , we want to respond with some html content that is customized using the 23456789 and 678543 strings.
A picture might help here
Here’s how this was achieved
location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" {
root /var/www/html/test/;
index template.html;
sub_filter_once off;
sub_filter '_first_param_' '$param1';
sub_filter '_second_param_' '$param2';
rewrite ^.*$ /template.html break;
}create a file named template.html with the following content in /var/www/html/test 
Breaking down the config one line at a time
location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" : The regex is essentially matching for the first set of digits after the / and adding that as the value for variable $param1. The first match is a series of 8 digits with each digit in the range 0-9. The second match is for a series of 6 digits with each digit in the range 0-9 and it will be added as the value for variable $param2
root /var/www/html/test/; : Specifying the root location for the location.
index template.html; : Specifying the home page for the location.
sub_filter_once off; : Specify to the sub_filter module to not stop after the first match for replacing response content. By default it processes the first match and stops.
sub_filter 'first_param' '$param1'; : Direct the sub_filter module to replace any text matching first_param in the response html with value in variable $param1.
sub_filter 'second_param' '$param2'; : Direct the sub_filter module to replace any text matching second_param in the response html with value in variable $param1.
rewrite ^.*$ /template.html break; : Specify nginx to server template.html regardless of the URI specified.
Big thanks to Igor for help with the configs!!
Over the last week, I moved this blog from a LAMP (Linux, Apache, MySQL, PHP) stack to LEMP (Linux, Nginx, MySQL, PHP) stack. Have a blog post in the works with all the gory details, but wanted to quick document a quirk in the WordPress + Nginx combination that broke permalinks on this site.
Permalinks are user friendly permanent static URLs for a blog post. So for example this particular blog post’ URL is
https://kudithipudi.org/2017/02/24/how-to-configure…press-permalinks/
instead of
https://kudithipudi.org/?p=1762
This works by default in Apache because WordPress puts in the required rewrite rules.
To get it work in Nginx, you have to add the following config in the Nginx site configuration
Under the / location context, add the following
try_files $uri $uri/ /index.php?$args;
This is essentially telling Nginx to try to display the URI as is, and if it fails that, pass the URI as an argument to index.php.
Command parameters for varnishlog to view the backend server that is processing the request. In this particular case, I wanted to see the request URL and backend server for any responses with HTTPÂ code 401 (unauthorized access)
sudo varnishlog -i BackendOpen,BereqURL -q "BerespStatus == 401"
Found this good article by Mark Huot regarding using curl to check websocket servers at http://www.thenerdary.net/post/24889968081/debugging-websockets-with-curl
curl -i -N -H "Connection: Upgrade" -H "Upgrade: websocket" -H "Host: echo.websocket.org" -H "Origin: http://www.websocket.org" http://echo.websocket.org
Just for my records
grep "WORD\|ANOTHER\|NEITHER" string
searches for either “WORD” or “ANOTHER” or “NEITHER” in string.
If you are using a Linux system that uses yum for package management (like Fedora, Centos, RHEL), you can use the following command to find out which package contains a file. This is useful when you want to figure out which package to install. For example, dig (DNS utility) doesn’t come pre-installed on the system. And running “sudo yum install dig” doesn’t do anything.
sudo yum whatprovides '*/dig'
This returns
Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile 32:bind-utils-9.8.2-0.47.rc1.el6.x86_64 : Utilities for querying DNS name servers Repo : base Matched from: Filename : /usr/bin/dig
breaking down the command options
whatprovides : Is used to find out which package provides some feature or file. Just use a specific name or a file-glob-syntax wildcards to list the packages available or installed that provide that feature or file.