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split /PATTERN/,EXPR
I read the following in a book,
When you use a pattern in split, be sure to avoid memory parantheses in the pattern since these trigger seperator retention mode.
I can't seem to find the documentation which explains this in detail. Could someone please explain Seperator Retention Mode and its possible usage briefly?
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A string is splitted based on delimiter specified by pattern. By default, it whitespace is assumed as delimiter. split syntax is: Split /pattern/, variableName.
split() is a string function in Perl which is used to split or you can say to cut a string into smaller sections or pieces. There are different criteria to split a string, like on a single character, a regular expression(pattern), a group of characters or on undefined value etc..
Using the split function: my $x='welcome'; my @arr=split (//, $x); print "@arr"; The split function is used to split the string $x by giving the delimiter as nothing. Since the delimiter is empty, split splits at every character, and hence all the individual characters are retrieved in the array.
I use the following perl code: ($First,$Last) = split "." , $string; I have also used: ($First,$Last) = split '.
This is documented in perldoc -f split towards the end (in-code commentary is my own):
If the
PATTERNcontains capturing groups, then for each separator, an additional field is produced for each substring captured by a group (in the order in which the groups are specified, as per backreferences); if any group does not match, then it captures theundefvalue instead of a substring. Also, note that any such additional field is produced whenever there is a separator (that is, whenever a split occurs), and such an additional field does not count towards theLIMIT. Consider the following expressions evaluated in list context (each returned list is provided in the associated comment):split(/-|,/, "1-10,20", 3) # ('1', '10', '20') # No retention, '-', ',' consumed split(/(-|,)/, "1-10,20", 3) # ('1', '-', '10', ',', '20') # Split on and retain '-' or ',' # 5 elements returned split(/-|(,)/, "1-10,20", 3) # ('1', undef, '10', ',', '20') # undef because '-' matches split(/(-)|,/, "1-10,20", 3) # ('1', '-', '10', undef, '20') # undef because ',' matches split(/(-)|(,)/, "1-10,20", 3) # ('1', '-', undef, '10', undef, ',', '20') # one match per capturing group. (-) matches -, but # (,) returns undef on trying to match -. # 7 elements (!)
So, two interesting quirks that may catch out the unwary:
The generation of undefs in list context whenever a capturing group does not match, but something else in PATTERN does
You might split with a capture group, specifying LIMIT as $n, and the resultant list has more than $n elements
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It means that if you use a regex with parentheses that generates back references, then the matched separators will be retained, and returned in the list, along with the split values.
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