From: "Peña, Botp" <botp@...>
Date: 2007-08-25T10:12:20+09:00
Subject: Re: How to append some data at the beginning of a file

On Behalf Of Uday Thokala:
# newfile = File.new("test1","w")
# newfile.puts "This line should appear at the top of each file";
# oldfile = File.open("test", "r+")
# oldfile.each_line { |line| newfile.puts line}
# oldfile.close();
# newfile.close();
# File.delete("test");
# File.rename("test1", "test");

that is nice, but it would be ideal if your code is immune to dependencies (like static filenames, fixed number of files, etc)

eg, consider the *nix cat command, you can easily insert lines at the beginning or end. In your case eg,

irb(main):006:0> system "ls -la test2.txt"
ls: test2.txt: No such file or directory
=> false
irb(main):007:0> system "cat test.txt"
1
2
3
this
is
a
test=> true
irb(main):008:0> text_insert="this will be inserted"
=> "this will be inserted"
irb(main):009:0> system "echo #{text_insert} | cat - test.txt"
this will be inserted
1
2
3
this
is
a
test=> true
irb(main):010:0> new_file="test2.txt"
=> "test2.txt"
irb(main):011:0> system "echo #{text_insert} | cat - test.txt > #{new_file}"
=> true
irb(main):012:0> system "ls -la test2.txt"
-rw-r--r-- 1 root root 42 Aug 25 09:02 test2.txt
=> true
irb(main):013:0> system "cat test2.txt"
this will be inserted
1
2
3
this
is
a
test=> true
irb(main):014:0>

note that cat is simply flexible. eg, 

    cat f - g

will concatenate file f, standard input, and file g in that order; thus inserting standard input bw the contents of files f and g.

i think ARGF is flexible enough. just a simple thought.

kind regards -botp