From: dblack@...
Date: 2007-01-03T19:50:27+09:00
Subject: Re: Delete line from file

Hi --

On Wed, 3 Jan 2007, Robert Klemme wrote:

> On 03.01.2007 00:11, Jules wrote:
>> Given a line number, what is the best way to delete this line from a
>> file?
>
> $ cat x
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> 10
>
> $ sed -ni -e '5 b;p' x
>
> robert@fussel /cygdrive
> $ cat x
> 1
> 2
> 3
> 4
> 6
> 7
> 8
> 9
> 10
>
> Or did you mean with Ruby?
>
> $ ruby -n -i.bak -e 'puts $_ unless $. == 5' x
>
> $ cat x
> 1
> 2
> 3
> 4
> 6
> 7
> 8
> 9
> 10
>
>> And given an array of line numbers, what is the best way to delete
>> these lines from a file?
>
> $ ruby -n -i.bak -e 'puts $_ unless [1,3,4].include? $.' x
>
> robert@fussel /cygdrive/c/Temp
> $ cat x
> 2
> 5
> 6
> 7
> 8
> 9
> 10
>
> $ diff -u x.bak x
> --- x.bak       2007-01-03 11:03:20.281250000 +0100
> +++ x   2007-01-03 11:03:46.437500000 +0100
> @@ -1,7 +1,4 @@
> -1
> 2
> -3
> -4
> 5
> 6
> 7
>
> Inside a script?
>
> robert@fussel /cygdrive/c/Temp
> $ ./del.rb x
>
> robert@fussel /cygdrive/c/Temp
> $ diff -u x.bak x
> --- x.bak       2007-01-03 11:09:29.437500000 +0100
> +++ x   2007-01-03 11:09:31.468750000 +0100
> @@ -2,7 +2,6 @@
> 2
> 3
> 4
> -5
> 6
> 7
> 8
>
> robert@fussel /cygdrive/c/Temp
> $ cat del.rb
> #!ruby
>
> f = ARGV.shift or raise "Need file name"
> fb = f + ".bak"
>
> File.rename(f, fb)
>
> File.open(f, "w") do |out|
>  File.foreach(fb) {|line| out.puts line unless $. == 5}
> end
>
>
> Plenty to choose from... :-)

For the script version you can also do:

#!/usr/local/bin/ruby -ni.bak
puts $_ unless $. == 5

(or some variant thereof).


David

-- 
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)