Modify the last two characters of a string in Perl
I am looking for a solution to a problem:
I have the NSAP address which is 20 characters long:
I now have to replace the last two characters of this string with F0 and the final string should look like:
My current implementation chops the last two characters and appends F0 to it:
my $nsap = "39250F800000000000000100011921680030081D"; chop($nsap); chop($nsap); $nsap = $nsap."F0";
Is there a better way to accomplish this?
You can use substr:
substr ($nsap, -2) = "F0";
substr ($nsap, -2, 2, "F0");
Or you can use a simple regex:
$nsap =~ s/..$/F0/;
This is from substr's manpage:
substr EXPR,OFFSET,LENGTH,REPLACEMENT substr EXPR,OFFSET,LENGTH substr EXPR,OFFSET Extracts a substring out of EXPR and returns it. First character is at offset 0, or whatever you've set $[ to (but don't do that). If OFFSET is nega- tive (or more precisely, less than $[), starts that far from the end of the string. If LENGTH is omitted, returns everything to the end of the string. If LENGTH is negative, leaves that many characters off the end of the string.
Now, the interesting part is that the result of substr can be used as an lvalue, and be assigned:
You can use the substr() function as an lvalue, in which case EXPR must itself be an lvalue. If you assign something shorter than LENGTH, the string will shrink, and if you assign something longer than LENGTH, the string will grow to accommodate it. To keep the string the same length you may need to pad or chop your value using "sprintf".
or you can use the replacement field:
An alternative to using substr() as an lvalue is to specify the replacement string as the 4th argu- ment. This allows you to replace parts of the EXPR and return what was there before in one oper- ation, just as you can with splice().
$nsap =~ s/..$/F0/;
replaces the last two characters of a string with F0.
Use the substr( ) function:
substr( $nsap, -2, 2, "F0" );
chop( ) and the related chomp( ) are really intended for removing line ending characters - newlines and so on.
I believe that substr( ) will be quicker than using a regular expression.