Python | Accepting Script Input

A lot of people use Python as a replacement for shell scripts, using it to automate common system tasks, such as manipulating files, configuring systems, and so forth. This article aims to describe accepting Script Input via Redirection, Pipes, or Input Files.

Problem – To have a script to be able to accept input using whatever mechanism is easiest for the user. This should include piping output from a command to the script, redirecting a file into the script, or just passing a filename, or list of filenames, to the script on the command line.

Python’s built-in fileinput module makes this very simple and concise if the script looks like this.



Code #1 :

filter_none

edit
close

play_arrow

link
brightness_4
code

import fileinput
  
with fileinput.input() as f_input:
    for line in f_input:
        print(line, end ='')

chevron_right






                        filter_none








Then input to the script can already be accepted in all of the previously mentioned ways. If the script is saved and make it executable then the one can get the expected output using all of the following:


Code #2 : 











                                    filter_none




                                    edit

                                    close




                                    play_arrow




                                    link

                                    brightness_4

                                    code
                                




















# Prints a directory listing to stdout. 


$ ls | ./filein.py  


  


# Reads/etc/passwd to stdout. 


$ ./filein.py/etc/passwd  


  


# Reads/etc/passwd to stdout. 


$ ./filein.py < /etc/passwd  



















                        chevron_right







                        filter_none








The fileinput.input() function creates and returns an instance of the FileInput class. In addition to containing a few handy helper methods, the instance can also be used as a context manager. So, to put all of this together, if one wrote a script that expected to be printing output from several files at once, one might have it include the filename and line number in the output, as shown in the code given below – 


Code #3 : 











                                    filter_none




                                    edit

                                    close




                                    play_arrow




                                    link

                                    brightness_4

                                    code
                                




















import fileinput 


with fileinput.input('/etc/passwd') as f: 


    for line in f: 


        print(f.filename(), f.lineno(), line, end ='') 



















                        chevron_right







                        filter_none










/etc/passwd1
/etc/passwd2
/etc/passwd3 

<other output omitted>


Using it as a context manager ensures that the file is closed when it’s no longer being used, and one leveraged a few handy FileInput helper methods here to get some extra information in the output.



          
          
          
          

            

    

        My Personal Notes
        arrow_drop_up
    

    

        
        

            
            
        

    


Recommended Posts:
Image
manikachandna97
Check out this Author's contributed articles.
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on  the "Improve Article" button below.