(poorly written, revise)

which Interpreter?

This simple program shows how many days remain until a future date.

Simply add this script to ~/bin (or another folder in your path) and make it executable.

#!/Users/fy/anaconda3/bin/python
# daysleft: a program to show how many days are left until a future date

import datetime

# input
event='The Exam'
future_date=datetime.date(2019,3,28)

#
today=datetime.date.today()
days_left=future_date-today

print(f'Today is {today}')
print(f'{days_left.days} days are left until {event} on {future_date}')

Note: The first line is the output of

azizcodes$ which python
/Users/fy/anaconda3/bin/python

Executing,

azizcodes$ daysleft
Today is 2019-03-18
10 days are left until The Exam on 2019-03-28

which is shorter than writing python script.py each time.

A More Flexible Way

A more flexible way of specifying the interpreter is using #!/usr/bin/env python. From Stackoverflow

#!/usr/bin/python is hardcoded to always run /usr/bin/python, while #!/usr/bin/env python will run whichever python would be default in your current environment (it will take in account for example $PATH, you can check which python interpreter will be used with which python). The second way ( #!/usr/bin/env python ) is preferred , as it’s not dependent on particular installation. It will work for example with virtualenv setups or systems where there is no /usr/bin/python, but only e.g. /usr/local/bin/python.

Calling Python from with Bash

Here is an example. Call this file python_from_bash.

#!/bin/bash

python_code(){
cat << EOF
# script.py
import datetime
event='The Exam'
future_date=datetime.date(2019,3,28)
today=datetime.date.today()
days_left=future_date-today
print(f'Today is {today}')
print(f'{days_left.days} days are left until {event} on {future_date}')
EOF
}

python -c "$(python_code)"

Now run

azizcodes$ python_from_bash

and it should execute. This has the advantage of having a whole program contained in one file, if that’s what you want. Ofcourse, you can run the following just as easily

#!/bin/bash

python script.py

Speaking of Executing Strings..

bash -c string

This command executes string. This opens the possibility of getting a string through curl and executing it on the fly, such is done by Homebrew (with Ruby, though, but same idea)

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

which can be an easy and transparent way of installing scripts. Unfortunately, as famous Homebrew is, I haven’t seen people use this trick. But I am gonna change that, because it’s too elegant!

A Start-Up Script

Here is a small project: I have my preferences saved in my .bash_profile but I have many devices. It would be nice if I can have one folder of user scripts synchronized across all of them. By downloading a git file (and pulling the updated version, if it is already there) and then copying the scripts to the ~/bin/ folder and making them executable.

All in one command:

bash -c "$(curl -fsSL https://raw.githubusercontent.com/azizcodes/myscripts/master/download)" 

which executes this script.

This command will do the following

Download the following files to ~/projects/myscripts (or update that folder if it exists, through a git pull)
README
bin_info, run this command to show usage instructions
add_profile, run this command to copy the .bash_profile
bashprofile, for your reference, a list of shell function
download, for your reference, the script to download myscripts
Copies the scripts to ~/bin
Make them executable

Workflow

To upload, make changes and push them to the shared repository from the device
To download, just execute the above command

PS: I know I can just simply clone ~/bin from a git repository and keep it synchronized, which is probably a lot easier. But I wanted to test and illustrate this method.