perl regex substring

To match strings that start with a ! you need this pattern. The ^ is the anchor at the beginning of the string.

/^!/

If you want to capture the stuff after the !, you need this pattern. The parenthesis () are a capture group. They tell Perl to grab everything between them and keep it. The . means any character, and the + is a quantifier for as many as possible, at least one. So .+ means grab everything.

/^!(.+)/

To apply it, do this.

$str =~ m/^!(.+)/;

And to get the "bypass" out of that pattern, use the $1 match variable that was assigned automatically by Perl with the m// operation.

print $1; # will print bypass

To make that conditional, it would be:

print $1 if $str =~ m/^!(.+)/;

The if here is in post-fix notation, which lets you omit the block and the parenthesis. It's the same as the following, but shorter and easier to read for single statements.

if ( $str =~ m/^!(.+)/ ) {
    print $1;
}

If you want to permanently change $str to not have an exclamation mark at the beginning, you need to use a substitution instead.

$str =~ s/^!//;

The s/// is the substitution operator. It changes $str in place. The original value including the ! will be lost.

Use ^!\K.+.

It works this way:

• ^! - Match initial ! (but this will soon change, see below).
• \K - Keep - "forget" about what you have matched so far and set the starting point of the match here (after the !).
• .+ - Match non-empty sequence of chars.

Due to \K, only the last part (.+) is actually matched.