Xxaxx's Xperimint #7 -- Playing with PERL -- Split Function

Xxaxx's Xperimints #7
Split Function
Playing with PERL

Let's play around with parsing shall we?

In Perl you can parse an expression (slit it up) using a statement such as the following:

@an_array = split(/marker/,"Some string to split.");

@an_array -- is the array that will recieve the results of the spliting process.

split -- is the function that splits the string up. (But then you probably figured that out.)

marker -- is the letter or substring to look for to split the string up with.

"Some string to split." -- is the string to split.

; -- is the ever important semi-colon without which Perl freaks out.

So let's try this:

@an_array = split(//,".");

Name:
split - split up a string using a regexp delimiter

Synopsis:
split /PATTERN/,EXPR,LIMIT

split /PATTERN/,EXPR

split /PATTERN/

split

Description:
Splits a string into an array of strings, and returns it. By default, empty leading fields are preserved, and empty trailing ones are deleted.

If not in list context, returns the number of fields found and splits into the @_ array. (In list context, you can force the split into @_ by using ?? as the pattern delimiters, but it still returns the list value.) The use of implicit split to @_ is deprecated, however, because it clobbers your subroutine arguments.

If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, splits on whitespace (after skipping any leading whitespace). Anything matching PATTERN is taken to be a delimiter separating the fields. (Note that the delimiter may be longer than one character.)

If LIMIT is specified and positive, splits into no more than that many fields (though it may split into fewer). If LIMIT is unspecified or zero, trailing null fields are stripped (which potential users of pop() would do well to remember). If LIMIT is negative, it is treated as if an arbitrarily large LIMIT had been specified.

A pattern matching the null string (not to be confused with a null pattern //, which is just one member of the set of patterns matching a null string) will split the value of EXPR into separate characters at each point it matches that way. For example:

    print join(':', split(/ */, 'hi there'));

produces the output 'h:i:t:h:e:r:e'.

The LIMIT parameter can be used to split a line partially

    ($login, $passwd, $remainder) = split(/:/, $_, 3);

When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT one larger than the number of variables in the list, to avoid unnecessary work. For the list above LIMIT would have been 4 by default. In time critical applications it behooves you not to split into more fields than you really need.

If the PATTERN contains parentheses, additional array elements are created from each matching substring in the delimiter.

    split(/([,-])/, "1-10,20", 3);

produces the list value

    (1, '-', 10, ',', 20)

If you had the entire header of a normal Unix email message in $header, you could split it up into fields and their values this way:

    $header =~ s/\n\s+/ /g;  # fix continuation lines
    %hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

The pattern /PATTERN/ may be replaced with an expression to specify patterns that vary at runtime. (To do runtime compilation only once, use /$variable/o.)

As a special case, specifying a PATTERN of space (' ') will split on white space just as split() with no arguments does. Thus, split(' ') can be used to emulate awk's default behavior, whereas split(/ /) will give you as many null initial fields as there are leading spaces. A split() on /s+/ is like a split(' ') except that any leading whitespace produces a null first field. A split() with no arguments really does a split(' ', $_) internally.

Example:

    open(PASSWD, '/etc/passwd');
    while (<PASSWD>) {
        ($login, $passwd, $uid, $gid,
         $gcos, $home, $shell) = split(/:/);
        #...
    }

(Note that $shell above will still have a newline on it. See chop, chomp, and join.)

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