how to run piece of code just before the exit of perl script

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旧巷少年郎
旧巷少年郎 2021-01-02 03:20

In my script, I need to load some info from disk file and during the run of script the info might be changed.To keep the consistence of the file in disk and it\'s in memory

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  • 2021-01-02 03:57

    I think you're looking for END block:

    END {
        # cleanup
    }
    

    An END code block is executed as late as possible, that is, after perl has finished running the program and just before the interpreter is being exited, even if it is exiting as a result of a die() function. (But not if it's morphing into another program via exec, or being blown out of the water by a signal--you have to trap that yourself (if you can).) You may have multiple END blocks within a file--they will execute in reverse order of definition; that is: last in, first out (LIFO). END blocks are not executed when you run perl with the -c switch, or if compilation fails.

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  • 2021-01-02 04:02

    There's two different ways to do this, depending on what you're looking for.

    • The END block is executed when the interpreter is shut down. See the previous answer for more details :)
    • The DESTROY block/sub, that is executed when your object goes out of scope. That is, if you want to embed your logic into a module or class, then you can use DESTROY.

    Take a look at the following example (it's a working example, but some details like error checking, etc.. are omitted):

    #!/usr/bin/env perl
    
    package File::Persistent;
    
    use strict;
    use warnings;
    use File::Slurp;
    
    sub new {
        my ($class, $opt) = @_;
    
        $opt ||= {};
    
        my $filename = $opt->{filename} || "./tmpfile";
        my $self = {
            _filename => $filename,
            _content => "",
        };
    
        # Read in existing content
        if (-s $filename) {
            $self->{_content} = File::Slurp::read_file($filename);
        }
    
        bless $self, $class;
    }
    
    sub filename {
        my ($self) = @_;
        return $self->{_filename};
    }
    
    sub write {
        my ($self, @lines) = @_;
        $self->{_content} .= join("\n", @lines);
        return;
    }
    
    sub DESTROY {
        my ($self) = @_;
        open my $file_handle, '>', $self->filename
            or die "Couldn't save persistent storage: $!";
        print $file_handle $self->{_content};
        close $file_handle;
    }
    
    # Your script starts here...
    package main;
    
    my $file = File::Persistent->new();
    
    $file->write("Some content\n");
    
    # Time passes...
    $file->write("Something else\n");
    
    # Time passes...
    $file->write("I should be done now\n");
    
    # File will be written to only here..
    
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  • 2021-01-02 04:06

    to handle Control-C you need to handle signals (no END block is triggered). It could be done next:

    $SIG{INT}  = \&signal_handler;
    $SIG{TERM} = \&signal_handler;
    
    sub signal_handler {
        #implement here pre exit logic
        die "\n";
    }
    
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