Re: Forward slashes around argument

The forward slashes are signify a "regular expression". Regular Expressions. A regex can match a series of characters within a variable and much, much more than that. Be careful with syntax like "if this variable doesn't match 'not stop'" - that is a double negative and is hard to understand.

Update: italics added to main point. Extraneous \ removed before single quotes.

use strict;
use warnings;

my @CPC_STP_type =('bus does not stop here','bus stop', 'anything', 'n
+ot this stop');

foreach my $type (@CPC_STP_type)
{
    if ($type =~ m/not stop/)  #the "m" is optional
    {
       print "type=$type......'not stop' detected\n";
    }
    else
    {
       print "type=$type......'not stop' was NOT detected\n";
    }
}
print "\n";

=prints
type=bus does not stop here......'not stop' detected
type=bus stop......'not stop' was NOT detected
type=anything......'not stop' was NOT detected
type=not this stop......'not stop' was NOT detected
=cut

foreach my $type (@CPC_STP_type)
{
    if ($type !~ m/not stop/)  #the "m" is optional
    {
       print "type=$type......We stop here\n";
    }
    else
    {
       print "type=$type......We keep going\n";
    }
}
__END__
#watch out for the unexpected!

type=bus does not stop here......We keep going
type=bus stop......We stop here
type=anything......We stop here
type=not this stop......We stop here <= Whoa!!
[download]

Comment on Re: Forward slashes around argument Download Code

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Re^2: Forward slashes around argument by hippo (Bishop) on Jul 02, 2019 at 08:03 UTC
`print "type=$type......\'not stop\' detected\n";` You might be pleased to hear that those backslashes before the single-quotes are superfluous. If you omit them your code will become shorter to type and simpler to eye-parse: `print "type=$type......'not stop' detected\n";` [download] HTH.	[reply] [d/l] [select]
Re^3: Forward slashes around argument by Marshall (Canon) on Jul 04, 2019 at 04:13 UTC
You are quite correct. My point was: Be careful with syntax like "if this variable doesn't match 'not stop'" - that is a double negative and is hard to understand.. Perl quoting can become hard to understand. An extraneous \ in this case makes little difference, but thanks for pointing that out.	[reply]


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