From: Alex Gutteridge <alexg@...>
Date: 2007-07-10T13:02:33+09:00
Subject: Re: Simple string operation

On 10 Jul 2007, at 11:54, 12 34 wrote:

> seqNo =
> File.basename("/Volumes/MINOLTA1/DCIM/100MLT16/PICT0004.MOV",".*") 
> [-1,3].to_s
> seqNo = "-" + seqNo+ ".xx.m"
> puts "seqNo: #{seqNo} " # >> seqNo: -4.xx.m
>
> but I want it to be -004.xx.m. In other words I want the leading  
> zeros.
>
> I didn't even think the .to_s should be necessary, but tried it in
> desperation.
>
> Thanks

Your use of String#[] is wrong:

-------------------------------------------------------------- String#[]
      Element Reference---If passed a single +Fixnum+, returns the code
      of the character at that position. If passed two +Fixnum+ objects,
      returns a substring starting at the offset given by the first, and
      a length given by the second.

So [-1,3] gives you a string starting at the last character that is 3  
characters long. You run off the end of the string before it gets to  
3 characters, so it ends up just being the last character - 4. I  
wonder if Ruby shouldn't raise an IndexError in that case.

Replace it with [-4,4] to get what you want (I think) - the last 4  
characters. As you mention, the .to_s is unnecessary.

seqNo = File.basename("/Volumes/MINOLTA1/DCIM/100MLT16/ 
PICT0004.MOV",".*")[-4,4]
seqNo = "-#{seqNo}.xx.m"

Alex Gutteridge

Bioinformatics Center
Kyoto University