Rule the command-line with ruler.py!

By Vasudev Ram

While working at the command-line, I came up with the idea for this little Python utility which displays a ruler on the console. You can use this program's output as a ruler, to find the character positions and lengths of parts of your own program's output on the line, or to measure the lengths of fields in fixed-length or variable-length records in a text file or CSV file which you need to process via your program. And of course, your program can be in any language, not just Python.

Note: the program is written assuming a console width of 80 characters. You can change some of the values in it if you need it to work with a console of a different width.

I've called it ruler.py. Here is the code for it:

"""
# ruler.py - A program to display a ruler on the command line.
Copyright 2014 Vasudev Ram - http://www.dancingbison.com
Program to display a line on the command-line screen.
The line consists of repeated occurrences of the characters:
0123456789, concatenated.
Purpose: By running this program, you can use its output as a ruler,
to find the position of your own program's output on the line, or to 
measure the lengths of fields in fixed- or variable-length records in a text file,  
fields in CSV files, etc.
"""

import sys

def ruler(units="0123456789", repeats=8, fives=True):
    for i in range(repeats):
        if i < repeats - 1:
            if fives:
                sys.stdout.write(str(i) + (" " * 4) + "5" + (" " * 4))
            else:
                sys.stdout.write(str(i) + (" " * 9))
        else:
            if fives:
                sys.stdout.write(str(i) + (" " * 4) + "5" + (" " * 3))
            else:
                sys.stdout.write(str(i) + (" " * 8))
    sys.stdout.write("\n")
    #sys.stdout.write(units * repeats + "\n")
    sys.stdout.write(units * repeats)
    sys.stdout.flush()

def main():
    ruler()

if __name__ == "__main__":
    main()
# EOF

And here is its output:

$ python ruler.py
0    5    1    5    2    5    3    5    4    5    5    5    6    5    7    5
01234567890123456789012345678901234567890123456789012345678901234567890123456789
$

And the output from this call to ruler():

ruler(repeats=8, fives=False)

0         1         2         3         4         5         6         7
01234567890123456789012345678901234567890123456789012345678901234567890123456789

I've parameterized the values it uses, to some extent, so you can customize them. You can also import the file ruler.py as a module and call its ruler() function in your own Python program. The code for doing that is as simple as:

# test_ruler.py

from ruler import ruler

ruler()

The Wikipedia article on rulers is interesting. So is the Golomb ruler. And here is a rolling ruler:

- Vasudev Ram - Dancing Bison Enterprises

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