Question

I would like to format text content that I am getting as a stdout stream using column, but I fail. For instance, using a single line, all works fine:

$ echo "1 12 123 1234 1 12 123 1234 " | column -t
1  12  123  1234  1  12  123  1234

.. however, if I try to simulate an “endless” stream:

$ while true; do echo "1 12 123 1234 1 12 123 1234 "; sleep 1; done | column -t
^C

… there is simply no response, until one exits with Ctrl-C.

(Note that the while thing is just meant to simulate reading an endless stream from a device, as in ‘cat /dev/ttyUSB0‘)

This leads me to believe that, even if column by default should accept standard input, it needs a “complete” and finished file (that is, with a determined file size) in order to work; and in the case of an “endless” stream, that is not the case – so it never outputs anything.

Any suggestion on how I could achieve column formatting in this context? EDIT: Doesn’t necesarily have to be the column program; anything else that formats text into columns would be fine (but I’m afraid, for instance awk also needs a complete file)…

Thanks in advance,
Cheers!

Answer 1

I, too, found column disappointing in its inability to stream, and sdaau’s code in its inability to measure my columns. So here’s a fix for both those problems. Maybe not terribly efficient, but it’s just for debugging, anyway. I have it in my ~/bin folder as pcol (be sure to chmod +x it):

#!/usr/bin/env python
import sys

sep = ','
gutter = 2
for arg in sys.argv:
    if arg.startswith('-s'):
        sep = arg[2:]
    elif arg.startswith('-g'):
        gutter = int(arg[2:])

widths = []
while True:
    raw = sys.stdin.readline()
    line = raw.strip('\0').strip('\n')
    vals = line.split(sep)
    if len(vals) > len(widths):
        widths = [0] * len(vals)

    widths = [max(len(val) + gutter, width) for val, width in zip(vals, widths)]
    metaformat = '%%%ds' * len(widths)
    format = metaformat % tuple(widths)
    print format % tuple(vals)