breaking the loop

[Shaunn Johnson]

Howdy:

I'm trying to find the best solution for breaking
out of a loop when editing a list of files.

I have a script that:

* gets a list of files
* opens the files with a 'foreach $f(@list)'
* does a 'while <> { ... } close (FILE)'

The script works, but if I run it, it loops
continually and edits (then re-edits) the files.
I think I could use a lock file to do until I
get a particular file, but I'm not sure how
to go about it - at the same time, it may not be
the more productive way to go.

[--snip script--]
my @list = grep {/\.txt/ } readdir(DIR) or die "Can not read the dir\n";

# create a loop to search for instances of
# control characters and change it to something else


foreach $file(@list) {
open (FILE, $file) or die "can not open this file: $!";

local $^I=".bak"; # to keep a backup of the files
# set to "" if i don't want backups
local @ARGV = @list; # the files to work on
while (<>) {
s!$pattern!$new_ptrn!g ;
print;
} # end while loop
close (FILE);
} #end of for loop


close (DIR);

__END__
[/--snip script--]

Any suggestions? Thanks!

-X

[Paul Kraus]

Perldoc -f last
Perldoc -f next

-----Original Message-----
From: Johnson, Shaunn [mailto:SJohnson6@bcbsm.com]
Sent: Tuesday, September 16, 2003 4:22 PM
To: perl beginners
Subject: breaking the loop


Howdy:

I'm trying to find the best solution for breaking
out of a loop when editing a list of files.

I have a script that:

* gets a list of files
* opens the files with a 'foreach $f(@list)'
* does a 'while <> { ... } close (FILE)'

The script works, but if I run it, it loops
continually and edits (then re-edits) the files.
I think I could use a lock file to do until I
get a particular file, but I'm not sure how
to go about it - at the same time, it may not be
the more productive way to go.

[--snip script--]
my @list = grep {/\.txt/ } readdir(DIR) or die "Can not read the dir\n";

# create a loop to search for instances of
# control characters and change it to something else


foreach $file(@list) {
open (FILE, $file) or die "can not open this file: $!";

local $^I=".bak"; # to keep a backup of the files
# set to "" if i don't want backups
local @ARGV = @list; # the files to work on
while (<>) {
s!$pattern!$new_ptrn!g ;
print;
} # end while loop
close (FILE);
} #end of for loop


close (DIR);

__END__
[/--snip script--]

Any suggestions? Thanks!

-X

[Jeff 'Japhy' Pinyan]

On Sep 16, Johnson, Shaunn said:

>* gets a list of files
>* opens the files with a 'foreach $f(@list)'
>* does a 'while <> { ... } close (FILE)'
>
>The script works, but if I run it, it loops
>continually and edits (then re-edits) the files.
>I think I could use a lock file to do until I
>get a particular file, but I'm not sure how
>to go about it - at the same time, it may not be
>the more productive way to go.

Your code is doing too much work.

>my @list = grep {/\.txt/ } readdir(DIR) or die "Can not read the dir\n";

This creates the list of files.

>foreach $file(@list) {
>open (FILE, $file) or die "can not open this file: $!";
>
>local $^I=".bak"; # to keep a backup of the files
> # set to "" if i don't want backups
>local @ARGV = @list; # the files to work on

Perhaps you mean

local @ARGV = $file;

instead.

> while (<>) {
> s!$pattern!$new_ptrn!g ;
> print;
> } # end while loop
> close (FILE);
>} #end of for loop

Better yet, remove the for loop. I'll show the code in a moment.

>close (DIR);

That should be closedir().

You can do this without opendir(), and without grep() or the for loop.

{
local $^I = ".bak";
local @ARGV = glob "$directory/*.txt";
while (<>) {
s/foo/bar/g;
print;
}
}

Ta da!

--
Jeff "japhy" Pinyan [email]japhy@pobox.com[/email] [url]http://www.pobox.com/~japhy/[/url]
RPI Acacia brother #734 [url]http://www.perlmonks.org/[/url] [url]http://www.cpan.org/[/url]
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]

[John W. Krahn]

Shaunn Johnson wrote:

>
> Howdy:

Hello,

> I'm trying to find the best solution for breaking
> out of a loop when editing a list of files.
>
> I have a script that:
>
> * gets a list of files
> * opens the files with a 'foreach $f(@list)'
> * does a 'while <> { ... } close (FILE)'
>
> The script works, but if I run it, it loops
> continually and edits (then re-edits) the files.
> I think I could use a lock file to do until I
> get a particular file, but I'm not sure how
> to go about it - at the same time, it may not be
> the more productive way to go.
>
> [--snip script--]
> my @list = grep {/\.txt/ } readdir(DIR) or die "Can not read the dir\n";
>
> # create a loop to search for instances of
> # control characters and change it to something else
>
> foreach $file(@list) {
> open (FILE, $file) or die "can not open this file: $!";
>
> local $^I=".bak"; # to keep a backup of the files
> # set to "" if i don't want backups
> local @ARGV = @list; # the files to work on
> while (<>) {

You are looping through all the files in @list using foreach above and
then you are looping through all the files in @list using while (<>).
This means that you are modifying each file the number of times for each
file in the directory. Are you sure this even works at all because you
are not prepending the directory name to the file name?

> s!$pattern!$new_ptrn!g ;
> print;
> } # end while loop
> close (FILE);
> } #end of for loop
>
> close (DIR);
>
> __END__

Something like this should work:

my $dir = '/home/someone';
local $^I = '.bak'; # to keep a backup of the files
# set to "" if i don't want backups

opendir DIR, $dir or die "Cannot open $dir: $!";
local @ARGV = map "$dir/$_", grep /\.txt$/, readdir DIR;
close DIR;

# create a loop to search for instances of
# control characters and change it to something else

while ( <> ) {
s!$pattern!$new_ptrn!g;
print;
} # end while loop

__END__



John
--
use Perl;
program
fulfillment

[R. Joseph Newton]

Jeff 'japhy' Pinyan wrote:

> You can do this without opendir(), and without grep() or the for loop.
>
> {
> local $^I = ".bak";
> local @ARGV = glob "$directory/*.txt";
> while (<>) {
> s/foo/bar/g;
> print;
> }
> }
>
> Ta da!
>

Score one for Japhy!

This is the first time I have seen the diamond or in-place editing operator
used well. Usually I blanch when I see them--the diamond conjures up the
image of some poor shmuck typing in lists of filenames at the command-line,
and the in-place suggests a delusory "economy" where there really is none in
the processing itself.. Here, with the encapsulation within a small block,
the immediacy of the assignment of @ARGV relative to its use in feeding the
diamond, and the overall brevity of the code, it makes good sense and makes
the process more clear by abstracting the [in this case] irrelevant details of
file access.

Thanks,

Joseph

[James Edward Gray II]

On Saturday, September 27, 2003, at 01:57 PM, R. Joseph Newton wrote:

> This is the first time I have seen the diamond or in-place editing
> operator
> used well. Usually I blanch when I see them--the diamond conjures up
> the
> image of some poor shmuck typing in lists of filenames at the
> command-line...

This seems a strange thing to say, to me. The diamond operator is
simple a shortcut to implementing the UNIX filter methodology, which I
believe has done quite well proving it's usefulness over the years.

James