Browsing CategoryOld Notes

Use eval To Timeout a Section Of Code

eval {
    local $SIG{__DIE__} = "DEFAULT";
    local $SIG{ALRM} = sub { die "timeout" };

    # Tells OS to send alarm signal after 10 secs

    # your chunk of code that could time out
    while(1) {
        # do something
if ($@ =~ /timeout/) {
    print "Timed out";
} elsif ($@) {
    # some other error caught

# the rest of your code here


  1. Set the alarm inside the eval.
  2. Can’t use eq on $@ since it will contain something like “timeout at line 10”. Have to use pattern.

How To Check If a Perl Module Exists

To quickly check if a certain module is installed in your environment, do this from the command line

perl -MModuleName -e 1

If the prompt comes back with no message, then the module exists. Otherwise, if it comes back with a “Can’t Locate…” message, it’s not available.

Cleanup Leading and Trailing Whitespaces

Here’s a regular expression to remove the leading and trailing whitespaces from a string:

$str =~ s/^s*//;    # remove leading whitespaces
$str =~ s/s*$//;    # remove trailing whitespaces

I have often seen this used to do the same thing:

$str =~ s/s*(.*?)s*$/$1/;

According to the book Mastering Regular Expressions by Jeffrey E.F. Friedl, this is slower. The reason he says is that “with each character, before allowing the dot to match, the ‘*?’ must try to see whether what follows can match. That’s a lot of backtracking, particularly since it’s the kind that goes in and out of the parenthesis.”

Output Logging Routine

This code will allow logging into a file and optionally, to the screen as well. This will create the file if necessary.

sub mlog {
    my ($msg) = @_;
    open (FH, ">> /tmp/logfile.log")
        or croak "error opening logfile: $!n";

    my $timestamp = localtime;
    print FH "$timestamp: $msgn";
    close FH;

    print "$timestamp: $msgn";    # also log to the screen

And to use this in your code:

mlog("This is a test log");