From: Robert Klemme <shortcutter@...>
Date: 2007-01-03T19:15:10+09:00
Subject: Re: Delete line from file

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... :-)

Kind regards

	robert