how to display output in a uniformed manner in tcl

Question

I have a doubt regarding format command. my output is kind of cluster and ununiform like below

    24-04-2011    16:07  <DIR>  Administrator 
    15-05-2011 16:05 <DIR> confuser 
    01-02-2011   20:57  <DIR>  Public 

What should I do in order to display the output in a proper and uniform manner. all in beginning in the same column. like this :

Yeah i used this command puts [format {%-s %-4s %-8s} $user\t $date\t $time] its giving me output like:

Administrator 15-05-2011 16:05 
confuser 01-02-2011 20:57 
Public 29-01-2011 19:28 
TechM 30-04-2011 09:47

The output am receiving is according to the number of letters present in the first string such as administrator confuser public techm. so what i need to know is how to get a output which doesn't take into account the length of the first string and give a proper uniform columned output.

Answer 1

The cheap hack method is to use tabs as separators (“\t” instead of “”) in your output string. That will work for small amounts of variation, but won't handle wide variations (or small variations around your current terminal/editor's tab width).

To do the job properly, you need to first get a list of all the conceptual lines you want to print out (i.e., the data but not yet formatted). Then you go through each line and work out the width needed for each field, taking the maximum across the whole dataset. With that, you can then configure the format string for format. Here's an example (for Tcl 8.5) where everything is just being formatted as strings:

proc printColumnarLines {lines} {
    foreach fields $lines {
        set column 0
        foreach field $fields {
            set w [string length $field]
            if {![info exist width($column)] || $width($column) < $w} {
                set width($column) $w
            }
            incr column
        }
    }
    foreach fields $lines {
        set column 0
        foreach field $fields {
            puts -nonewline [format "%-*s " $width($column) $field]
            incr column
        }
        puts ""; # Just the newline please
    }
}

The * in the format string in that position means to take another argument specifying the width of that field. I'm not surprised you missed it though; format strings are actually a very dense micro-language and it is easy to skip over an important bit. (That's true for all other languages that use them too; very few people know all that you can do with them.)

You can do much more intelligent things with fixed sets of fields, and other %-sequences support the * too. Mind you, I usually have to experiment to get exactly what I want (especially with floating point numbers…)