Custom scripts and more on Flask

This week our task was the following on the Linux course:

a) Create a new command in Linux and set it up to work as a script for every user.
b) Create a script that handles command line arguments.
c) Create a Flask app that has multiple paths.
d) Create a Flask app that uses templates.
e) optional: use c and d in a production-like environment
f) optional: read user input in Flask.
g) optional: Create a Flask app that reads user input from a form and calculates the area of a square.

Creating a new script for all users

I wrote a basic bash script that prints the username and date and tested it in my home folder. Then I changed the permissions so that everyone can read and execute it but not modify it. I then copied it to the /usr/bin folder so that everyone could use it by just issuing the script name. Then I created a new test user, logged into it and tested again.

nano userinfo
./userinfo

#!/bin/bash
DATE="$(date +'%y/%m/%d')"
NAME="$(whoami)"
printf "Hello ${NAME}!\nThe date is: ${DATE}"

userinfo

chmod +x userinfo
chmod g-w userinfo
sudo cp userinfo /usr/bin/
ls -l /usr/bin/userinfo
    -rwxr-xr-x 1 root root 102 Oct  1 12:23 /usr/bin/userinfo
sudo adduser test
su test
userinfo

userinfo

A script with command line parameters

For this script I decided to just do some basic arithmetic and then some checking for arguments. If there are no arguments, or the argument is not an integer, you get an error message.

#!/bin/bash
RE='^[0-9]+$'
if [ $# -eq 0 ] ; then
    echo "No arguments given. Requires 1 argument."
else
    if ! [[ $1 =~ $RE ]] ; then
        echo "Given argument is not a valid number"
    else
        CUBE=$(($1*$1*$1))
        echo $CUBE
    fi
fi

cubed-script

A Flask app with multiple paths

As a basic Flask app with just a landing page looks like this:

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
        return "Flask site works"

app.run(debug=True)

curl localhost:5000
Flask site works

I can create another route on the app by creating another function and declaring a different route with the @app.route notation.

#...
@app.route("/test")
def test():
        return "testing routes"

@app.route("/asdf")
def test2():
        return "testing routes 2"

app.run(debug=True)

routes

Flask Templates

To use templates I need to create a templates sub-folder in the directory that the app is run from and create an html file. I then need to import render_template in the python file and use it in the route that I want to.

mkdir templates
nano templates/basic.html

<!doctype html>
<html>
       <head>
               <title>Flask Template</title>
               <meta charset="utf-8">
       </head>
       <body>
               <h1>{{ title }}</h1>
       </body>
</html>

from flask import Flask, render_template
#...
@app.route("/template")
def test2():
       return render_template("basic.html", title="Template Works")
#...