Question

I discovered this while using ruby printf, but it also applies to C’s printf.

If you include ANSI colour escape codes in an output string, it messes up the alignment.

Ruby:

ruby-1.9.2-head > printf "%20s\n%20s\n", "\033[32mGreen\033[0m", "Green"
      Green          # 6 spaces to the left of this one
               Green # correctly padded to 20 chars
 => nil

The same line in a C program produces the same output.

Is there anyway to get printf (or something else) to align output and not add spaces for non-printed characters?

Is this is a bug, or is there a good reason for it?

Update: Since printf can’t be relied upon to align data when there’s ANSI codes and wide chars, is there a best practice way of lining up coloured tabular data in the console in ruby?

Answer 1

I disagree with your characterization of ‘9 spaces after the green Green’. I use Perl rather than Ruby, but if I use a modification of your statement, printing a pipe symbol after the string, I get:

perl -e 'printf "%20s|\n%20s|\n", "\033[32mGreen\033[0m", "Green";'
      Green|
               Green|

This shows to me that the printf() statement counted 14 characters in the string, so it prepended 6 spaces to produce 20 characters right-aligned. However, the terminal swallowed 9 of those characters, interpreting them as colour changes. So, the output appeared 9 characters shorter than you wanted it to. However, the printf() did not print 9 blanks after the first ‘Green’.

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Regarding the best practices for aligned output (with colourization), I think you’ll need to have each sized-and-aligned field surrounded by simple ‘%s’ fields which deal with the colourization:

printf "%s%20.20s%s|%s%-10d%s|%s%12.12s%s|\n",
       co_green, column_1_data, co_plain,
       co_blue,  column_2_data, co_plain,
       co_red,   column_3_data, co_plain;

Where, obviously, the co_XXXX variables (constants?) contain the escape sequences to switch to the named colour (and co_plain might be better as co_black). If it turns out that you don’t need colourization on some field, you can use the empty string in place of the co_XXXX variables (or call it co_empty).