From: Robert Klemme <bob.news@...>
Date: 2005-05-04T22:30:07+09:00
Subject: Re: writing to a file with gsub!

Ralf M�ller wrote:
> Hi,
>
> i simply want so change an existing file
>
> ram@lilith:~/src/ruby$cat test
> 123 wer ---
> 245545 hzrzu ----
> 245 dfgdfh --
>
>
> and i thought that
>
> irb(main):012:0> file = File.open('test');  file.each do |line|
> line.gsub!(/\d+/,'###') end
>
> would do this, because each iterates accross the file.
> But nothing is changed.
>
> Where are my mistakes??

As others have pointed out, reading and writing to the same file at a time
is quite complicated.  Your approach could only work with memory mapped
files...

But it's simpler - as simple as

ruby -pi.bak -e 'gsub /\d+/, "###"' your_file

In case you wonder about the parameter's meanings:

15:23:01 [source]: ruby -h
Usage: ruby [switches] [--] [programfile] [arguments]
  -0[octal]       specify record separator (\0, if no argument)
  -a              autosplit mode with -n or -p (splits $_ into $F)
  -c              check syntax only
  -Cdirectory     cd to directory, before executing your script
  -d              set debugging flags (set $DEBUG to true)
  -e 'command'    one line of script. Several -e's allowed. Omit
[programfile]
  -Fpattern       split() pattern for autosplit (-a)
  -i[extension]   edit ARGV files in place (make backup if extension
supplied)
  -Idirectory     specify $LOAD_PATH directory (may be used more than
once)
  -Kkcode         specifies KANJI (Japanese) code-set
  -l              enable line ending processing
  -n              assume 'while gets(); ... end' loop around your script
  -p              assume loop like -n but print line also like sed
  -rlibrary       require the library, before executing your script
  -s              enable some switch parsing for switches after script
name
  -S              look for the script using PATH environment variable
  -T[level]       turn on tainting checks
  -v              print version number, then turn on verbose mode
  -w              turn warnings on for your script
  -W[level]       set warning level; 0=silence, 1=medium, 2=verbose
(default)
  -x[directory]   strip off text before #!ruby line and perhaps cd to
directory
  --copyright     print the copyright
  --version       print the version

15:24:54 [temp]: echo "asdasda123sdasdsd" > your_file
15:25:03 [temp]: cat your_file
asdasda123sdasdsd
15:25:11 [temp]: ruby -pi.bak -e 'gsub /\d+/, "###"' your_file
15:25:15 [temp]: cat your_file
asdasda###sdasdsd
15:25:16 [temp]: cat your_file.bak
asdasda123sdasdsd

Kind regards

    robert