reading file after a particular line in file

V

Vandana

Hello All,

I would like to read a file in ruby. It is a 2G file, but
contain useless data in the beginning portion of the file.

There is a particular pattern towards the middle of the file after
which useful data begins. Is there a way to grep for this pattern and
then read every line henceforth, but ignore all lines previous to line
on which pattern found?

Thanks,
Vandana
 
T

Thomas Volkmar Worm

File.open("myfile", "r") do |f|

# Skip the garbage before pattern:
while f.gets !~ /pattern/ do; end

# Read your data:
while l = f.gets
puts l
end

end
 
R

Robert Klemme

There's also the flip flop operator:

File.foreach "myfile" do |line|
if /pattern/ =~ line .. false
puts line
end
end

The trick I am using is that the FF operator starts to return true if
the first expression returns true and stays true until the last
expression returns true - in this case never since you want to read
until the end of the file.

Kind regards

robert
 
U

Une Bévue

Robert Klemme said:
There's also the flip flop operator:

File.foreach "myfile" do |line|
if /pattern/ =~ line .. false
puts line
end
end

The trick I am using is that the FF operator starts to return true if
the first expression returns true and stays true until the last
expression returns true - in this case never since you want to read
until the end of the file.
Click to expand...

coud that trick be used for start and stop tags ? like :

File.foreach "myfile" do |line|
if /<body/ =~ line .. /<\/body/ =~ line
puts line
end
end

if true, that's clever !
 
R

Robert Klemme

coud that trick be used for start and stop tags ? like :

File.foreach "myfile" do |line|
if /<body/ =~ line .. /<\/body/ =~ line
puts line
end
end

if true, that's clever !
Click to expand...

Yes, that could be done. However, I would not use this for languages
from the SGML family (XML, HTML) because there are no guarantees as to
how many tags you'll find on a single line of text. There are better
tools do deal with that (REXML, Nokogiri...).

Kind regards

robert
 
U

Une Bévue

Robert Klemme said:
Yes, that could be done. However, I would not use this for languages
from the SGML family (XML, HTML) because there are no guarantees as to
how many tags you'll find on a single line of text. There are better
tools do deal with that (REXML, Nokogiri...).
Click to expand...

Right, however REXML isn't working for badly balanced tags.
I dis some test, today, of Nokogiri, it works even better than tidy for
the first step cleaning unbalanced tags.

the only question i have about Nokogiri is how to avoid the DOCTYPE
because it outputs :
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">

even if i'm using #to_xhtml :

then, the DOCTYPE is wrong...
 

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