Learning Perl on Win32 Systems

The split and join Functions

Regular expressions can be used to break a string into fields. The split function does this and the join function glues the pieces back together.

The split Function

The split function takes a regular expression and a string and looks for all occurrences of the regular expression within that string. The parts of the string that don’t match the regular expression are returned in sequence as a list of values. For example, here’s something to parse semicolon-separated fields, such as the PATH environment variable:

$line = "c:\\;;c:\\windows\\;c:\\windows\\system;";
@fields = split(/;/,$line); # split $line, using ; as delimiter
# now @fields is ("c:\", "", "c:\windows","c:\windows\system")

Note how the empty second field became an empty string. If you don’t want this to happen, match all of the semicolons in one fell swoop:

@fields = split(/;+/, $line);

This matches one or more adjacent semicolons together, so that there is no empty second field.

One common string to split is the $_ variable, and that turns out to be the default:

$_ = "some string";
@words = split(/ /); # same as @words = split(/ /, $_);

For this split, consecutive spaces in the string to be split will cause null fields (empty strings) in the result. A better pattern would be / +/, or ideally /\s+/, which matches one or more whitespace characters together. In fact, this pattern is the default pattern,^[55] so if you’re splitting the $_ variable on whitespace, you can use all the defaults and merely ...