# Newbie question on an I/O loop **URL:** \ **Category:** ruby-talk\ **Created:** [16 July 2006 08:25 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007 "2006-07-16T08:25:43Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Jay\_Daniels](https://avatars.discourse-cdn.com/v4/letter/j/a5b964/32.png) [@Jay\_Daniels](https://rubytalk.org/u/Jay_Daniels)\ **Post date:** [16 July 2006 08:25 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007/1 "2006-07-16T08:25:43Z")
I got a question that's puzzling me. Am new to Ruby but programming for decades. Here's the problem. This apparently simple loop reads 396 bytes of a file and no more. The actual file is 1.5KB and I can display it easily in a hex dumper. The bytes Ruby has read are all correct. It just seems to stop after 396 bytes. Any idea what's wrong or where I should be looking? Many thanks in advance, JK Daniels > > > code \>\>\> if ARGV[0] == nil     puts( "\n" + $help ) else     i = 0     tfm = File.open( ARGV[0] )     tfm.each\_byte{ |c| i = i + 1; printf( "%d: %X\n", i, c ) }     if tfm.eof         puts "at eof" else puts "not at eof"     end end \<\<\< end code \<\<\< This outputs the first 396 bytes and then state it's at EOF. If it makes any difference, the last three bytes it reads are (all hex): C0 A4 00 and the next three (unread) bytes in the file are: 1A C0 B5 > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Forum](https://avatars.discourse-cdn.com/v4/letter/f/43a26b/32.png) [@Forum](https://rubytalk.org/u/Forum)\ **Post date:** [16 July 2006 10:14 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007/2 "2006-07-16T10:14:48Z")
> I got a question that's puzzling me. Am new to Ruby but programming for > decades. Here's the problem. Welcome to the red world This apparently simple loop reads 396 bytes > of a file and no more. The actual file is 1.5KB and I can display it > easily in a hex dumper. The bytes Ruby has read are all correct. It just > seems to stop after 396 bytes. Any idea what's wrong or where I should > be looking? > > Many thanks in advance, > > JK Daniels > > \>\>\> code \>\>\> > > if ARGV[0] == nil >     puts( "\n" + $help ) > else >     i = 0 >     tfm = File.open( ARGV[0] ) >     tfm.each\_byte{ |c| i = i + 1; printf( "%d: %X\n", i, c ) } >     if tfm.eof >         puts "at eof" else puts "not at eof" >     end > end > > \<\<\< end code \<\<\< > > This outputs the first 396 bytes and then state it's at EOF. If it makes > any difference, the last three bytes it reads are (all hex): C0 A4 00 > and the next three (unread) bytes in the file are: 1A C0 B5 Hmm you are not reading a binary file under windows by any chance? In that case File.open needs a mode "rb". Anyway the ruby way to do what you want is more like this File.open ARGV.first, "rb" do # I would put paranthesis, but just to demonstrate the                                               # various possibilities                \>file\>                i = 0                file.each\_byte {                         \>c\>                         i += 1                        puts "%d:%X" % [i, c]                } end puts "at eof ;)" Cheers Robert > **···** > > On 7/16/06, Jay Daniels \ wrote: > > -- > > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > -- > Deux choses sont infinies : l'univers et la bêtise humaine ; en ce qui > concerne l'univers, je n'en ai pas acquis la certitude absolue. > > - Albert Einstein ---
**Author:** ![Steven\_R](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Steven\_R](https://rubytalk.org/u/Steven_R)\ **Post date:** [16 July 2006 13:25 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007/3 "2006-07-16T13:25:06Z")
Jay Daniels wrote: > I got a question that's puzzling me. Am new to Ruby but programming for decades. Here's the problem. This apparently simple loop reads 396 bytes of a file and no more. The actual file is 1.5KB and I can display it easily in a hex dumper. The bytes Ruby has read are all correct. It just seems to stop after 396 bytes. Any idea what's wrong or where I should be looking? > > Many thanks in advance, > > JK Daniels > > > > > code \>\>\> > > if ARGV[0] == nil >     puts( "\n" + $help ) > else >     i = 0 >     tfm = File.open( ARGV[0] ) >     tfm.each\_byte{ |c| i = i + 1; printf( "%d: %X\n", i, c ) } >     if tfm.eof >         puts "at eof" else puts "not at eof" >     end > end > > \<\<\< end code \<\<\< > > This outputs the first 396 bytes and then state it's at EOF. If it makes any difference, the last three bytes it reads are (all hex): C0 A4 00 and the next three (unread) bytes in the file are: 1A C0 B5 I tested this on a file that was 29,184 bytes - it worked fine. Could it be something in your data or environment? Sorry I couldn't be of more help. ---
**Author:** ![ts1](https://avatars.discourse-cdn.com/v4/letter/t/a8b319/32.png) [@ts1](https://rubytalk.org/u/ts1)\ **Post date:** [16 July 2006 13:48 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007/4 "2006-07-16T13:48:29Z")
> and the next three (unread) bytes in the file are: 1A C0 B5                                                       ^^^ moulon% /usr/bin/ruby -e 'p "%c" % 0x1A' "\032" moulon% it's Control-Z, use "rb" to open the file p.s.: moulon% ruby -e 'p "%c" % 0x1A' -e:1: [BUG] Segmentation fault ruby 1.9.0 (2006-07-14) [i686-linux] Aborted moulon% Guy Decoux ---
**Author:** ![Jay\_Daniels](https://avatars.discourse-cdn.com/v4/letter/j/a5b964/32.png) [@Jay\_Daniels](https://rubytalk.org/u/Jay_Daniels)\ **Post date:** [17 July 2006 06:31 UTC](https://rubytalk.org/t/newbie-question-on-an-i-o-loop/29007/5 "2006-07-17T06:31:28Z")
Thank you Guy, Steven, and Robert for solving the problem. I appreciate it. Never occurred to me it could be a control-z problem. Robert, thanks especially for showing the same code using typical Ruby metaphors. This also helps a lot. J K Daniels > > > re \>\>\> ts wrote: > **···** > > > \> and the next three (unread) bytes in the file are: 1A C0 B5 > >                                                       ^^^ > > moulon% /usr/bin/ruby -e 'p "%c" % 0x1A' > > "\032" > > moulon% > > > > it's Control-Z, use "rb" to open the file > > > > p.s.: > > > > moulon% ruby -e 'p "%c" % 0x1A' > > -e:1: [BUG] Segmentation fault > > ruby 1.9.0 (2006-07-14) [i686-linux] > > > > Aborted > > moulon% > > > > Guy Decoux > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).