How do I delete the first n characters on a line

[CyCliC]

How do I delete the first n characters on a line

Originally posted as a Categorized Question.

[jmcnamara]

Use substr:

    # substr EXPR,OFFSET,LENGTH,REPLACEMENT

    my $n    = 3;

    my $str1 = "1234567890\n";
    my $str2 = substr($str1, $n);

    print $str1; # 1234567890
    print $str2; # 4567890


John.
--

[ar0n]

substr($str, 0, $n) = "";

[tachyon]

You could also use a regex although this is not as fast as substr.

my $n = 3;

my $str = "1234567890\n";
$str =~ s/^.{$n}//s;
# was: $str =~ s/^.{$n}(.*)$/$1/s;
print $str;

The difference with the regex solution is that if $n > length $str no change will be made. With substr you will get a null string left in $str if you try to delete more chars than exist in $str. You need the /s modifier to make the . match a newline which is a valid char.

cheers

tachyon

To get the same behavior as a substr solution use: $str =~ s/^.{1,$n}//s;

Edit by tye to incorporate I0's reply

[I0]

#a simpler regex is
$str =~ s/^.{$n}//s #or, if you want a null string left in $str if you try to delete more chars than exist in $str,
$str =~ s/^.{1,$n}//s

[abstracts]

# substr EXPR,OFFSET,LENGTH,REPLACEMENT

    my $n    = 3;

    my $str1 = "1234567890\n";
    print $str1; # 1234567890
    
    substr($str1,0,$n,'');
    print $str1; # 4567890

Aziz,,,

Originally posted as a Categorized Answer.

[bikeNomad]

Another interesting thing about substr is that it can be assigned to (it's an lvalue). So if you really wanted to delete the characters, you could do this:

my $line = "abcdefghijk";
# delete the first 3 characters:
substr($line, 0, 3) = '';
print $line; # "defghijk"

Originally posted as a Categorized Answer.

[Anonymous Monk]

regexes carry with them a performance penalty.
there is nothing wront with just:

$foo = substr($foo,$n) unless(length $foo => $n);

or

$substr($foo,0,$n)="" unless(length $foo => $n);

or

$substr($foo,0,$n,'') unless(length $foo => $n);

this is generally faster than a regex ;-)

Originally posted as a Categorized Answer.

[alfie]

Given that you have the line in $_ and substitute the n with the amount of characters you'd like to delete:

s/^.{n}//;

Originally posted as a Categorized Answer.