Prior to Perl version 5.10, the result of using an lvalue multiple times was unspecified. $_ = 'a' print $x,' ' # prints 1a4, as above With negative offsets, it remembers its position from the end of the string when the target string is modified: my $x = '1234' Note that the lvalue returned by the three-argument version of substr acts as a 'magic bullet' each time it is assigned to, it remembers which part of the original string is being modified for example: my $x = '1234' # $s is now 'The black cat jumped from the green tree' My $z = substr $s, 14, 7, 'jumped from' # climbed my $s = 'The black cat climbed the green tree' This allows you to replace parts of the EXPR and return what was there before in one operation, just as you can with splice. Substr($name, 7) = 'gap' # raises an exceptionĪn alternative to using substr as an lvalue is to specify the replacement string as the 4th argument. A Perl string has the length that depends on the amount of memory in your system, which is theoretically unlimited. A string can contain ASCII, UNICODE and escape sequences characters such as. My $oops = substr $name, 7 # returns undef, with warning In Perl, a string is a sequence of characters surrounded by some kinds of quotation marks. My $null = substr $name, 6, 2 # returns '' (no warning) Substr($name, 4) = 'dy' # $name is now 'freddy' Here's an example showing the behavior for boundary cases: my $name = 'fred'

When used as an lvalue, specifying a substring that is entirely outside the string raises an exception. If the substring is beyond either end of the string, substr returns the undefined value and produces a warning. If OFFSET and LENGTH specify a substring that is partly outside the string, only the part within the string is returned.

To keep the string the same length, you may need to pad or chop your value using sprintf. 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. You can use the substr function as an lvalue, in which case EXPR must itself be an lvalue. My $end = substr $s, 14 # climbed the green tree My $middle = substr $s, 4, -11 # black cat climbed the If LENGTH is negative, leaves that many characters off the end of the string. If LENGTH is omitted, returns everything through the end of the string. If OFFSET is negative, starts that far back from the end of the string. # substr EXPR,OFFSET,LENGTH,REPLACEMENT # substr EXPR,OFFSET,LENGTH # substr EXPR,OFFSETĮxtracts a substring out of EXPR and returns it.

Perl string compare