ruby string format formatting

Question

I have a set of filenames named like the following

"file001" "file0001" ...
"file002" "file0002" ...
...
"file100" "file0100" ...
...

The pattern is pretty obvious:

name, padded_number

So if I wanted to use string formatting for the files in the first column I would just write

"%s%3d" %[name, number]"

But this hardcodes the padding (3). How can I make it so that I can specify the pad as a variable as well and somehow format the provided integer to use the specified padding?

Cody Caughlan · Accepted Answer · 2012-05-02 18:35:26Z

11

Use string interpolation:

padding = 9
"%s%#{padding}d" %[name, number]

answered May 2, 2012 at 18:35

Cody Caughlan

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4 Comments

steenslag Over a year ago

This results in "file" followed by 8 spaces and a "1".

Adrian Pronk Over a year ago

Don't you need a 0 in there? "%s%0#{padding}d"

Cody Caughlan Over a year ago

You guys are right but it still answers his core question, namely embedding a variable in the format string. Yes, his actually format string needs to be tweaked.

Sebastian Over a year ago

format("%s%0#{padding}d", name, number) passes Ruby's style guide validation

tokland · Accepted Answer · 2013-05-09 18:24:38Z

9

prefix = "file"
number = "1"
padding = 4
filename = prefix + number.rjust(padding, '0') #=> "file0001"

edited May 9, 2013 at 18:24

tokland

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answered May 2, 2012 at 18:53

steenslag

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