Extract information in a line of text with a format from user input

Question

I am trying to make a program which takes in input song files and a format to write metatags in file. Here is a few examples of the call:

• ./parser '%n_-_%t.mp3' 01_-_Respect.mp3 gives me track=01; title=Respect
• ./parser '%b._%n.%t.mp3' The_Queen_of_Soul._01.Respect.mp3 gives me album=The_Queen_of_Sould; track=01; title=Respect
• ./parser '%a-%b._%n.%t.mp3' Aretha_Franklin-The_Queen_of_Soul._01.Respect.mp3 gives me artist=Aretha_Franklin; track=01; title=Respect
• ./parser '%a_-_%b_-_%n_-_%t.mp3' Aretha_Franklin_-_The_Queen_of_Soul_-_01_-_Respect.mp3 gives me artist=Aretha_Franklin; track=01; title=Respect

For a call on the file 01_-_Respect.mp3, I'd like to have a variable containing 01, and the other Respect.

Here %n and %t represents respectively the number and the title of the songs. The problem is that I don't know how to extract this information in bash (or eventually in python).

My biggest problem is that I don't know the format in advance!

Note: There is more information than this, for example %b for the album, %a for the artist etc.

Answer 1

Well, you can use the string method split to split the string by _-_.

and for taking the input from the command line, you can use sys.argv to get that.

here's an example:

import sys
number,title = sys.argv[1].split("_-_")

Update:

Surely you can pass the pattern as a first argument and the file as the second argument like that:

import sys
pattern = sys.argv[1]
number,title = sys.argv[2].split(pattern)

Now if you need more complex and dynamic processing, then Regex is your winning card!

And in order to write a good regex, you got to understand your data and your problem or you'll end up writing a glitchy regex

Answer 2

You can elaborate on this. It is a very simple example, though.

import re
p = re.compile('([0-1][0-1])_\-_(.*)\.mp3')
title = '01_-_Respect.mp3'
p.findall(title)

Output [('01', 'Respect')]

I use this page to play with regex.

Update

Since the format is given, go with string slicing. Ok, pretty limited to the specific case..

number = title[:title.find('_')]
>>> number
'01'
>>> track = title[len(number) + 3:len(title)-4]
>>> track
'Respect'

Answer 3

Try This code:

(considering argument is given in runtime)

tmp=$1
num=echo ${tmp%%_*}
title=echo ${tmp##*_}|cut -d. -f1

Variables num and title will store the parts from the argument