File input/output: Difference between revisions
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(→{{header|Ruby}}: Task changed at 14 February 2012. Create a variable, instead of just passing the value. Remove many extra details and explanations. To copy a file block by block, just use FileUtils.) |
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=={{header|Ruby}}== |
=={{header|Ruby}}== |
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In general, open both files in binary mode. |
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<lang ruby> |
<lang ruby>str = File.open('input.txt', 'rb') {|f| f.read} |
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File.open('output.txt', 'wb') {|f| f.write str}</lang> |
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If 'input.txt' is a text file, we may forget binary mode. If no pathname begins with a pipe '|', then we may use ''IO::read'' and ''Kernel#open''. (The pipe is a problem, because <code>IO.read('| uname')</code> or <code>open('| sh', 'w')</code> would open a subprocess and not a file.) |
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It also works with open IO handles. |
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<lang ruby> |
<lang ruby># Only if 'input.txt' is a text file! |
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# Only if pipe '|' is not first character of path! |
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str = IO.read('input.txt') |
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FileUtils.copy_stream(i, o) |
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end |
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end</lang> |
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---- |
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We can also do IO with only the core library. |
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<lang ruby> |
<lang ruby>require 'fileutils' |
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FileUtils.copy_file 'input.txt', 'output.txt'</lang> |
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File.open('output.txt', 'wb') do |o| |
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buf = "" |
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bufsiz = (i.stat.blksize or 16384) |
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while i.read(bufsiz, buf) do o.write(buf) end |
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end |
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end</lang> |
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* The best buffer size is <code>i.stat.blksize</code>. Some platforms return <code>nil</code> there, so we guess 16384 bytes. |
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The shortest way to copy a file, without coding any loops and without requiring any libraries, is to read the entire file into memory. |
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<lang ruby>irb(main):001:0> open('output.txt', 'w') {|f| f << IO.read('input.txt')} |
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=> #<File:output.txt (closed)></lang> |
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But this has disadvantages: |
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* 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>, but this requires Ruby 1.9. (There is no way to pass 'b' flag to IO.read with Ruby 1.8.) |
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* If the file is too large, we fail to allocate enough memory. |
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---- |
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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. |
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{{works with|Ruby|1.9}} |
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<lang ruby>IO.copy_stream('input.txt', 'output.txt') |
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# It also works with open IO handles. |
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File.open('input.txt', 'rb') do |i| |
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File.open('output.txt', 'wb') do |o| |
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IO.copy_stream(i, o) |
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end |
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end</lang> |
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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. |
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=={{header|Run BASIC}}== |
=={{header|Run BASIC}}== |
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