Question concerning ruby file access

ruby-talk
1

Question concerning ruby file access from a novice:

I have seen following code fragment from

http://www.rubycentral.com/pickaxe/tut_io.html

File.open("testfile", "r") do |aFile|
# ... process the file
end

Advantage of this notation is that file is automatically closed when do
loop terminates -- maybe by an exception with Process.exit.

But how do I test in this notation that the file with name "testfile"
really exits (and opening was successful). In an multi-tasking
environment another process may delete the file just before this
statement is executed.

Or in other words: I want to print a text like "File with filename
"testfile" does not exist" when opening failed.

Best regards

Stefan Salewski

2

Stefan Salewski wrote:

But how do I test in this notation that the file with name "testfile"
really exits (and opening was successful). In an multi-tasking
environment another process may delete the file just before this
statement is executed.

If you want to completely avoid race conditions, you don't check - you just do
and then recover from eventual errors (i.e. you rescue the exception).

HTH,
Sebastian

···

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Jabber: sepp2k@jabber.org
ICQ: 205544826

3

# Or in other words: I want to print a text like "File
# with filename "testfile" does not exist" when opening failed.

i usually think it like db's logical unit of work or transaction. i just wrap it w ruby's begin/end and a rescue check as mentioned by sebastian.

something like eg

begin

* File.open("test.rbx") do |f|
* end

rescue =>e
  p e.message
end

"No such file or directory - test.rbx"
=> nil

note, you can have more rescues and finetune them. you can also make your own exceptions.. just continue reading on the pickaxe..

···

From: Stefan Salewski [mailto:mail@ssalewski.de]

4

begin
  File.open("testfile") do |aFile|
    ...
  end
rescue IOError => e
  #handle error
end

···

On Thu, 30 Oct 2008 00:14:57 +0000, Stefan Salewski wrote:

Question concerning ruby file access from a novice:

I have seen following code fragment from

http://www.rubycentral.com/pickaxe/tut_io.html

File.open("testfile", "r") do |aFile| # ... process the file
end

Advantage of this notation is that file is automatically closed when do
loop terminates -- maybe by an exception with Process.exit.

But how do I test in this notation that the file with name "testfile"
really exits (and opening was successful). In an multi-tasking
environment another process may delete the file just before this
statement is executed.

Or in other words: I want to print a text like "File with filename
"testfile" does not exist" when opening failed.

Best regards

Stefan Salewski

--
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/