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File input/output: Difference between revisions
→{{header|Ruby}}: Show FileUtils.copy_file, FileUtils.copy_stream, a copy loop, and IO.copy_stream. There are now 6 ways to copy a file.
(→{{header|Java}}: Attempt at Java 7 (no compiler on my current system), I'll handle the exceptions when I can test it) |
(→{{header|Ruby}}: Show FileUtils.copy_file, FileUtils.copy_stream, a copy loop, and IO.copy_stream. There are now 6 ways to copy a file.) |
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=={{header|Ruby}}==
This task is easy, with 'fileutils' from the standard library.
File.open('output.txt', 'w') do |file|▼
<lang ruby>require 'fileutils'
FileUtils.copy_file 'input.txt', 'output.txt'</lang>
end▼
</lang>▼
It also works with open IO handles.
<lang ruby>File.open('input.txt', 'rb') do |i|
FileUtils.copy_stream(i, o)
▲ end
▲end</lang>
----
We can also copy a file with only the core language.
<lang ruby>File.open('input.txt', 'rb') do |i|
File.open('output.txt', 'wb') do |o|
buf = ""
bufsiz = (i.stat.blksize or 16384)
while i.read(bufsiz, buf) do o.write(buf) end
end
end</lang>
* The best buffer size is <code>i.stat.blksize</code>. Some platforms return <code>nil</code> there, so we guess 16384 bytes.
The shortest way to copy a file, without coding any loops and without requiring any libraries, is to read the entire file into memory.
<lang ruby>irb(main):001:0> open('output.txt', 'w') {|f| f << IO.read('input.txt')}
=> #<File:output.txt (closed)></lang>
But this has disadvantages:
* There was no 'b' flag, so it might not work with binary files on some platforms. With a 'b' flag, the code would be <code>open('output.txt', 'wb') {|f| f << IO.read('input.txt', mode: 'rb')}</code>
* If the file is very large, we fail to allocate enough memory.
----
Ruby 1.9 has a new core method, <code>IO.copy_stream</code>. With [[MRI]] 1.9, <code>IO.copy_stream</code> might use [[Linux]]'s [http://www.kernel.org/doc/man-pages/online/pages/man2/sendfile.2.html sendfile(2)] system call, or it might loop with a buffer of 16384 bytes.
{{works with|Ruby|1.9}}
<lang ruby>IO.copy_stream('input.txt', 'output.txt')
# It also works with open IO handles.
File.open('input.txt', 'rb') do |i|
File.open('output.txt', 'wb') do |o|
IO.copy_stream(i, o)
end
end</lang>
FileUtils knows about IO.copy_stream; so if you use FileUtils, then your program uses IO.copy_stream with Ruby 1.9, but still works with older Ruby versions.
=={{header|Scala}}==
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