Navigating Files by Line Number

[John Baker]

Hi

I've tried the following code on Win XP, Ruby 1.8rc1 and
Mac OS X 10.3, Ruby 1.6.8. From the online documentation I
pretty much copied and tried the following code:

f = File.new("testfile.txt")
puts f.gets >> This is line 1
puts f.gets >> This is line 2
f.lineno = 9 >>
puts f.lineno >> 9
puts f.gets >> This is line 3

Although f.lineno updates to 9, it never seems to affect
the line number next read.

Thanks
John
______________________________________________________________
Herbalife Independent Distributor http://www.healthiest.co.za

 

[Jason Wold]

That seems to fit with the ri description of File.lineno=. It sets
lineno but doesn't seem to seek to that line in the file. I think
what you want could be achieved by:

f.rewind
1.upto(9) { f.readline }

or even extending the File class to add a function that does this

Class File
def seek_line(line)
self.rewind
1.upto(line) { self.readline }
end
end

Cheers,
Jason

 

[George Ogata]

I've tried the following code on Win XP, Ruby 1.8rc1 and
Mac OS X 10.3, Ruby 1.6.8. From the online documentation I
pretty much copied and tried the following code:

f = File.new("testfile.txt")
puts f.gets >> This is line 1
puts f.gets >> This is line 2
f.lineno = 9 >>
puts f.lineno >> 9
puts f.gets >> This is line 3

Although f.lineno updates to 9, it never seems to affect
the line number next read.

IO#lineno= just sets the counter, not the position in the file. This
is demonstrated in the ri example:

------------------------------------------------------------- IO#lineno=
ios.lineno = integer => integer
------------------------------------------------------------------------
Manually sets the current line number to the given value. +$.+ is
updated only on the next read.

f = File.new("testfile")
f.gets #=> "This is line one\n"
$. #=> 1
f.lineno = 1000
f.lineno #=> 1000
$. # lineno of last read #=> 1
f.gets #=> "This is line two\n"
$. # lineno of last read #=> 1001

 

[Ara.T.Howard]

Hi

I've tried the following code on Win XP, Ruby 1.8rc1 and
Mac OS X 10.3, Ruby 1.6.8. From the online documentation I
pretty much copied and tried the following code:

f = File.new("testfile.txt")
puts f.gets >> This is line 1
puts f.gets >> This is line 2
f.lineno = 9 >>
puts f.lineno >> 9
puts f.gets >> This is line 3

Although f.lineno updates to 9, it never seems to affect
the line number next read.

if the file is small:


line = IO.readlines 'testfile.txt'

p line[9]

Thanks
John
______________________________________________________________
Herbalife Independent Distributor http://www.healthiest.co.za

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