How can I match a pipe character followed by whitespace and another pipe?

Question

I am trying to find all matches in a string that begins with | |.

I have tried: if ($line =~ m/^\\\\\\|\\s\\\\\\|/) which didn\'t work. <

Answer 1

What about:

m/^\|\s*\|/ 

Answer 2

Pipe character should be escaped with a single backslash in a Perl regex. (Perl regexes are a bit different from POSIX regexes. If you're using this in, say, grep, things would be a bit different.) If you're specifically looking for a space between them, then use an unescaped space. They're perfectly acceptable in a Perl regex. Here's a brief test program:

my @lines = <DATA>;

for (@lines) {
    print if /^\| \|/;
}

__DATA__  
| | Good - space  
|| Bad - no space  
|   | Bad - tab  
 | | Bad - beginning space  
        Bad - no bars  

Answer 3

You are escaping the pipe one time too many, effectively escaping the backslash instead.

print "YES!" if ($line =~ m/^\|\s\|/);

Answer 4

If it's a literal string you're searching for, you don't need a regular expression.

my $search_for = '| |';
my $search_in = whatever();
if ( substr( $search_in, 0, length $search_for ) eq $search_for ) {
    print "found '$search_for' at start of string.\n";
}

Or it might be clearer to do this:

my $search_for = '| |';
my $search_in = whatever();
if ( 0 == index( $search_in, $search_for ) ) {
    print "found '$search_for' at start of string.\n";
}

You might also want to look at quotemeta when you want to use a literal in a regexp.

Answer 5

Remove the ^ and the double back-slashes. The ^ forces the string to be at the beginning of the string. Since you're looking for all matches in one string, that's probably not what you want.

m/\|\s\|/