How to pad a number with zeros to a specific length in tcl?

Question

I need to pad a number with a specific length (say 8) where the input number could be of any length.

Example: If the input number is 123456, I want to pad it as 12345600

If I knew that all input numbers would be of the same length (say 6), I would have done something like

[format "$input_num%02d" 0]

But since the input number can be of varied length, how do I achieve this? Obviously the below didn't work:

set cur_length [expr[llength[split $input_num ""]]
set padding [expr 8 - $cur_length]
set padded_num [format "$input_num%${padding}d" 0]

Any help is appreciated.

Thanks.

Answer 1

It's really simple, actually:

format %-08s $input_num

A number is also a string, so it can be left-justified like a string.

Documentation: format