Many built-in functions accept a regex pattern as an argument. Furthermore, any subroutine can accept a string yet treat it as a regex pattern. This could be done, for example, by passing the string to the match operator (
m//). Because regex patterns are encoded as regular strings, it is tempting to assume that a string literal will be treated as if a regex that matched only that string literal were supplied. Unexpected function behavior can result if the string contains characters that have special meanings when the string is treated as a regex pattern. Therefore, do not pass strings that are not clearly regex patterns to a function that takes a regex.
Noncompliant Code Example
This code example appears to split a list of names.
But the first argument to
split() is treated as a regex pattern. Because
$ indicates the end of the string, no splitting occurs.
This compliant solution passes a regex pattern to
split() as the first argument, properly specifying
$ as a raw character. Consequently,
@names is assigned the three names
STR31-PL-EX0: A string literal may be passed to a function if it normally takes a regex pattern but provides special behavior for that string. For example, the perlfunc manpage [Wall 2011] says, regarding
PATTERN, the first argument to
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 initial null fields (empty string) as there are leading spaces.