Need help with reading/writing to files

ruby-talk
1

I've been trying to write a program that will take a file, do some
find/replace operation and save the file. I'm pretty new to ruby, and I
can't seem to figure out how to do this succinctly. This is my latest
attempt, but it seems like I shouldn't need to open the file twice.

I tried to just open the file with "r+" permissions, but if I overwrote
it with a string that was shorter than the original contents, the extra
characters would stick around. I couldn't figure out how to slice off
the extra stuff I didn't need.

Any suggestions on how to reduce this to one call to File.open???
Thanks! Any other suggestions are also appreciated. Here's the code...

print "pattern:"
pattern = STDIN.gets.chop
print "replacement:"
replacement = STDIN.gets.chop
str = ""
ARGV.each do |file|
File.open(file,"r+") do |handle|
str = handle.read
end
File.open(file,"w+") do |handle|
str.gsub!(/#{pattern}/,replacement)
handle.write(str)
end
end

Thanks,

Ben

2

I've been trying to write a program that will take a file, do some
find/replace operation and save the file. I'm pretty new to ruby, and I
can't seem to figure out how to do this succinctly. This is my latest
attempt, but it seems like I shouldn't need to open the file twice.

I tried to just open the file with "r+" permissions, but if I overwrote
it with a string that was shorter than the original contents, the extra
characters would stick around. I couldn't figure out how to slice off
the extra stuff I didn't need.

Any suggestions on how to reduce this to one call to File.open???
Thanks! Any other suggestions are also appreciated. Here's the code...

print "pattern:"
pattern = STDIN.gets.chop
print "replacement:"
replacement = STDIN.gets.chop
str = ""
ARGV.each do |file|
File.open(file,"r+") do |handle|
str = handle.read
end
File.open(file,"w+") do |handle|
str.gsub!(/#{pattern}/,replacement)
handle.write(str)

  handle.truncate(handle.pos)

end
end

File#truncate(size) truncates the file to the given size. Passing your
current position after you write to the file truncates it immediately
after the last character you wrote.

HTH,
Mark

···

On Mon, 17 Jan 2005 14:11:07 +0900, Ben <bhbrinckerhoff@wustl.edu> wrote:

3

Ben wrote:

I've been trying to write a program that will take a file, do some
find/replace operation and save the file. I'm pretty new to ruby, and I
can't seem to figure out how to do this succinctly. This is my latest
attempt, but it seems like I shouldn't need to open the file twice.

Have you considered doing it all from the command line?

% ruby -pi -e 'gsub /pattern/, "replacement"' file1 file2...

···

--
Glenn Parker | glenn.parker-AT-comcast.net | <http://www.tetrafoil.com/&gt;

4

File#truncate was exactly what I was looking for. Thanks! Also, thanks
for the suggestion about the command line, I might try that as well,
but I might be making the script a little more complicated so it might
be a bit much for the command line. Thanks, both! I appreciate it.

Ben