To reuse code from an OCR’d book or a text file that has line numbers embedded in the file, say with example file
1 # cool program 2 import sys 3 def howneat(): 4 sys.exit('Thanks for visiting')
You can remove the line numbers by typing in Terminal:
perl -pe 's/^[ t]+d+//' neat.py > neater.py
The regular expression
\^ at the beginning of the line
[ t]+ match space or tab (one or more)
d+ match one or more digits
-p implicitly loop over (read each line of) the file
-e here is the PCRE to consider.
And we replace with nothing. This leaves alone the indentation of the code (relevant for Python).
I could have used the
-i flag to edit in place, but I instead redirected STDOUT to the file neater.py in case I made a mistake (inputting the wrong file, for example).