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Top Forums Shell Programming and Scripting Script to move the first line of a file to the end Post 302271626 by Altay_H on Friday 26th of December 2008 05:51:57 PM
Old 12-26-2008
Quote:
Originally Posted by Yogesh Sawant
using Perl:
Code:
# first_to_last.pl
my $file = shift;
open(FH, '<', $file)  or  die "Failed to read file $file : $! \n";
my $first_line      = <FH>;
my @remaining_lines = <FH>;
close(FH);

open(FH, '>', $file)  or  die "Failed to write file $file : $! \n";
print FH @remaining_lines;
print FH $first_line;
close(FH);

run this script as:
Code:
perl first_to_last.pl list.txt

Thanks. That works exactly as I need it to.



Quote:
Originally Posted by danmero
Code:
awk 'NR==1{store=$0;next}1;END{print store}' file

That does what I need it to, but it outputs the results to the console, whereas I need it to output it back to the file. I tried setting it equal to a variable and outputting that to a file, but that output the contents of the file separated by spaces rather than line breaks.

Here's what I tried:
Code:
#!/bin/bash
var=`awk 'NR==1{store=$0;next}1;END{print store}' list.txt`
echo $var > list.txt

Code:
$ cat ./list.txt
1
2
3
4
5
6
$ ./first_to_last.sh
$ cat ./list.txt
2 3 4 5 6 1

 

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Path::Class(3pm)					User Contributed Perl Documentation					  Path::Class(3pm)

NAME
Path::Class - Cross-platform path specification manipulation VERSION
version 0.26 SYNOPSIS
use Path::Class; my $dir = dir('foo', 'bar'); # Path::Class::Dir object my $file = file('bob', 'file.txt'); # Path::Class::File object # Stringifies to 'foo/bar' on Unix, 'fooar' on Windows, etc. print "dir: $dir "; # Stringifies to 'bob/file.txt' on Unix, 'bobfile.txt' on Windows print "file: $file "; my $subdir = $dir->subdir('baz'); # foo/bar/baz my $parent = $subdir->parent; # foo/bar my $parent2 = $parent->parent; # foo my $dir2 = $file->dir; # bob # Work with foreign paths use Path::Class qw(foreign_file foreign_dir); my $file = foreign_file('Mac', ':foo:file.txt'); print $file->dir; # :foo: print $file->as_foreign('Win32'); # foofile.txt # Interact with the underlying filesystem: # $dir_handle is an IO::Dir object my $dir_handle = $dir->open or die "Can't read $dir: $!"; # $file_handle is an IO::File object my $file_handle = $file->open($mode) or die "Can't read $file: $!"; DESCRIPTION
"Path::Class" is a module for manipulation of file and directory specifications (strings describing their locations, like '/home/ken/foo.txt' or 'C:WindowsFoo.txt') in a cross-platform manner. It supports pretty much every platform Perl runs on, including Unix, Windows, Mac, VMS, Epoc, Cygwin, OS/2, and NetWare. The well-known module "File::Spec" also provides this service, but it's sort of awkward to use well, so people sometimes avoid it, or use it in a way that won't actually work properly on platforms significantly different than the ones they've tested their code on. In fact, "Path::Class" uses "File::Spec" internally, wrapping all the unsightly details so you can concentrate on your application code. Whereas "File::Spec" provides functions for some common path manipulations, "Path::Class" provides an object-oriented model of the world of path specifications and their underlying semantics. "File::Spec" doesn't create any objects, and its classes represent the different ways in which paths must be manipulated on various platforms (not a very intuitive concept). "Path::Class" creates objects representing files and directories, and provides methods that relate them to each other. For instance, the following "File::Spec" code: my $absolute = File::Spec->file_name_is_absolute( File::Spec->catfile( @dirs, $file ) ); can be written using "Path::Class" as my $absolute = Path::Class::File->new( @dirs, $file )->is_absolute; or even as my $absolute = file( @dirs, $file )->is_absolute; Similar readability improvements should happen all over the place when using "Path::Class". Using "Path::Class" can help solve real problems in your code too - for instance, how many people actually take the "volume" (like "C:" on Windows) into account when writing "File::Spec"-using code? I thought not. But if you use "Path::Class", your file and directory objects will know what volumes they refer to and do the right thing. The guts of the "Path::Class" code live in the "Path::Class::File" and "Path::Class::Dir" modules, so please see those modules' documentation for more details about how to use them. EXPORT The following functions are exported by default. file A synonym for "Path::Class::File->new". dir A synonym for "Path::Class::Dir->new". If you would like to prevent their export, you may explicitly pass an empty list to perl's "use", i.e. "use Path::Class ()". The following are exported only on demand. foreign_file A synonym for "Path::Class::File->new_foreign". foreign_dir A synonym for "Path::Class::Dir->new_foreign". Notes on Cross-Platform Compatibility Although it is much easier to write cross-platform-friendly code with this module than with "File::Spec", there are still some issues to be aware of. o On some platforms, notably VMS and some older versions of DOS (I think), all filenames must have an extension. Thus if you create a file called foo/bar and then ask for a list of files in the directory foo, you may find a file called bar. instead of the bar you were expecting. Thus it might be a good idea to use an extension in the first place. AUTHOR
Ken Williams, KWILLIAMS@cpan.org COPYRIGHT
Copyright (c) Ken Williams. All rights reserved. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. SEE ALSO
Path::Class::Dir, Path::Class::File, File::Spec perl v5.14.2 2012-06-15 Path::Class(3pm)
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