rotate items in log file

[Robert Wallace]

in my code i'm trying to keep a log file of say 10 lines.
if a line is added and the log file is more than 10 lines, then the last
line is removed before a new line is added.
if the log file is less than 10 lines, then the new line will be added
and no lines will be removed.
here's my first attempt:


#append and clean logfile
my(@logFile);
open (READ, $logFile);
chomp(@logFile=<READ>);
close (READ);
my($size)=@logFile;
if ($size > 10){
unshift @logFile, $search;
pop @logFile;
}

my($logFileWrite)=join "\n", @logFile;
open (WRITE, ">$logFile");
print WRITE $logFileWrite;
close (WRITE);

the problem with unshift/pop here is that if there's only one line it'll
still rotate.
so I added the if statement. but if there are say 19 lines, it'll rotate
the 19 lines instead of trimming off 9.

is there a way perhaps to move 10 items from one array to another
like psudo code:
@arrayClean=@array [item 1], [item 2] ... [item 10]...throw out the
rest;

 

[Tad McClellan]

in my code i'm trying to keep a log file of say 10 lines.

Why don't you just use an existing wheel, such as Logfile::Rotate ?

if a line is added and the log file is more than 10 lines, then the last
line is removed before a new line is added.

open (READ, $logFile);

You should always, yes *always*, check the return value from open():

open (READ, $logFile) or die "could not open '$logFile' $!";

chomp(@logFile=<READ>);
close (READ);
my($size)=@logFile;

That does NOT get the size of the @logFile array, that gets the
1st element, same as:

my($size) = $logFile[0];

You need the name of the array in _scalar_ context if you want
to get the size:

my $size = @logFile;

if ($size > 10){

Here you already have a scalar context, so you don't even need the $size
temporary variable:

if (@logFile > 10) {

my($logFileWrite)=join "\n", @logFile;

Why did you chomp() them above only to put the newlines back in?

(and why no newline on the last element?)


I don't see any file locking going on. Is logging going on while
you are rotating the log?

is there a way perhaps to move 10 items from one array to another

You can also do it from one array back to the _same_ array.

like psudo code:
@arrayClean=@array [item 1], [item 2] ... [item 10]...throw out the
rest;

Yes, by using an "array slice":

@array = @array[ 0 .. 9 ];

or, in keeping with your write-only style:

@array=@array[0..9];


Space characters are not a scarce resource, feel free to use as many
as you like to make your code easier to read and understand.

 

[Gunnar Hjalmarsson]

in my code i'm trying to keep a log file of say 10 lines. if a line
is added and the log file is more than 10 lines, then the last line
is removed before a new line is added. if the log file is less than
10 lines, then the new line will be added and no lines will be
removed. here's my first attempt:

my($size)=@logFile;

--------^-----^
Remove those parentheses, or else $size is assigned the first line
rather than the number of lines.

if ($size > 10){
unshift @logFile, $search;
pop @logFile;
}

Try this instead:

unshift @logFile, $search;
splice @logFile, 10 if $size >= 10;

 

[Robert Wallace]

thanks folks. here's what I did:

in my code i'm trying to keep a log file of say 10 lines.

.....


That does NOT get the size of the @logFile array, that gets the
1st element, same as:

my($size) = $logFile[0];

You need the name of the array in _scalar_ context if you want
to get the size:

my $size = @logFile;

if ($size > 10){

got rid of the $size thing.

Here you already have a scalar context, so you don't even need the $size
temporary variable:

if (@logFile > 10) {


Why did you chomp() them above only to put the newlines back in?

(and why no newline on the last element?)
done.

I don't see any file locking going on. Is logging going on while
you are rotating the log?

I thought I keep it simple.
you think it'll be a problem without locking?

 

[Tad McClellan]

Tad McClellan wrote:

you think it'll be a problem without locking?

If you answer my question, then I will answer your question.


(the reason for asking the question was to determine whether
there might be a problem. But you did not answer it, so I
don't know if it will be a problem or not...
)

 

[Robert Wallace]

yes, it's possible.
I guess that's also my answer.

 

[Tad McClellan]

yes, it's possible.
I guess that's also my answer.

Yes, it will surely be a problem without locking.