Perl Cookbook

Processing Variable-Length Text Fields

Problem

You want to extract variable length fields from your input.

Solution

Use split with a pattern matching the field separators.

# given $RECORD with field separated by PATTERN,
# extract @FIELDS.
@FIELDS = split(/PATTERN/, $RECORD);

Discussion

The split function takes up to three arguments: PATTERN, EXPRESSION, and LIMIT. The LIMIT parameter is the maximum number of fields to split into. (If the input contains more fields, they are returned unsplit in the final list element.) If LIMIT is omitted, all fields (except any final empty ones) are returned. EXPRESSION gives the string value to split. If EXPRESSION is omitted, $_ is split. PATTERN is a pattern matching the field separator. If PATTERN is omitted, contiguous stretches of whitespace are used as the field separator and leading empty fields are silently discarded.

If your input field separator isn’t a fixed string, you might want split to return the field separators as well as the data by using parentheses in PATTERN to save the field separators. For instance:

split(/([+-])/, "3+5-2");

returns the values:

(3, '+', 5, '-', 2)

To split colon-separated records in the style of the /etc/passwd file, use:

@fields = split(/:/, $RECORD);

The classic application of split is whitespace-separated records:

@fields = split(/\s+/, $RECORD);

If $RECORD started with whitespace, this last use of split would have put an empty string into the first element of @fields because split would consider the record to have ...