Built-in String Handling Functions

Lending the power of regular expressions to some simple data-handling operations is a bit like giving a Kalashnikov to a small fish. It's simply overkill. To prevent ourselves from getting carried away and throwing away potential speed, we'll summarize the more useful of Perl's built-in string handling functions in Table C-1. Repeat after us:

We're only allowed to use regular expressions if the built-in functions won't hack it.

In this table, the Perl function is shown in lowercase (e.g., index ) and its replaceable parameters in uppercase (e.g., STRING ). As with most things in Perl, many of the functions in Table C-1 use $_ as a default EXPRESSION value, if no EXPRESSION value is supplied.

Table C-1. Built-in Perl string-handling functions

Function	Description
index STRING, SUBSTRING [,OFFSET]	Returns the position of the first SUBSTRING in STRING , where the first position is zero. If OFFSET is given, it tells index how many characters to skip before searching: index('Toad of Toad Hall', 'Toad') gives 0 index('Toad of Toad Hall', 'Toad', 1) gives 8 (-1 is returned if no match is found)
join EXPRESSION, LIST	Joins a LIST of strings into a single string, each separated by EXPRESSION (which can be an empty string, ""): join ":", "Badger", "Ratty", "Mole" gives Badger:Ratty:Mole
lc EXPRESSION	Lowercases EXPRESSION : lc "The Stoats took the Hall" gives the stoats took the hall
lcfirst EXPRESSION	Lowercases the first letter of EXPRESSION : lcfirst "MyBeautifulMind" gives myBeautifulMind
length EXPRESSION	Gives the length of EXPRESSION : length "Washerwoman" gives 11
reverse EXPRESSION	When used in a scalar context and with a single scalar, this reverses EXPRESSION : reverse "Poop poop, said Toad" gives daoT dias ,poop pooP ( reverse is also often used in a list context to reverse arrays, hashes, and other listy type things.)
rindex STRING, SUBSTRING [,POSITION]	Similar to index , this returns the position of the rightmost SUBSTRING in STRING . The optional POSITION is the rightmost position which is acceptable: rindex "Toad of Toad Hall", "Toad" gives 8 rindex "Toad of Toad Hall", "Toad", 7 gives 0 (-1 is returned if no match is found.)
split /PATTERN/, EXPRESSION, LIMIT	This function is the black sheep of the built-in string handling world, because it rather naughtily uses regular expressions to process the /PATTERN/ match, to split EXPRESSION strings into lists. After we've covered regular expressions proper, we'll come back to split , one of the most useful of the Perl munge operators.
sprintf FORMAT, LIST	Returns a formatted string in the manner of the ubiquitous printf conventions from the C programming language. The main sprintf Perl formatters are described in Table C-2. This is highly useful for reports .
substr EXPRESSION, OFFSET [,LENGTH] [,REPLACEMENT]	Extracts a substring out of EXPRESSION , starting at OFFSET , where the first position is zero: substr "Messing about in boats", 8 gives about in boats If OFFSET is negative, the count starts from the right-hand side of the string: substr "Messing about in boats", -8 gives in boats If LENGTH is omitted, everything to the end of the string is returned. Otherwise, LENGTH determines the length of the string returned: substr "Messing about in boats", 8, 5 gives about If LENGTH is negative, this is how many characters are left off the end of the substring: substr "Messing about in boats", 8, -5 gives about in The optional REPLACEMENT will replace the substring it finds in EXPRESSION : $stoat1 = "Messing about in boats"; $stoat2 = substr $stoat1, 0, 16, "Wonderful"; print $stoat1, "\n"; print $stoat2, "\n"; This produces: Wonderful boats Messing about in An alternative to using REPLACEMENT is to use substr on the left-hand side of an assignment operation: $stoat = "Messing about in boats"; substr ($stoat, 0, 16) = "Wonderful"; print $stoat, "\n"; This produces: Wonderful boats
uc EXPRESSION	Uppercases EXPRESSION : uc "canal barge " gives CANAL BARGE
ucfirst EXPRESSION	Uppercases the first character of EXPRESSION : ucfirst "railway engine" gives Railway engine

Table C-2. Perl formats for sprintf

Formatter	Description
%c	A character with the given number
%s	A string
%d	A signed integer, in decimal
%u	An unsigned integer, in decimal
%o	An unsigned integer, in octal
%x	An unsigned integer, in hexadecimal
%e	A floating-point number, in scientific notation (e.g., 1.00e+09 for 1 billion)
%f	A floating-point number, in fixed decimal notation
%g	A floating-point number, in either %e or %f notation
%X	Like %x , but using upper-case letters
%E	Like %e , but using an upper-case "E" (e.g., 1.00E+09)
%G	Like %g , but with an upper-case "E" (if applicable )
%b	An unsigned integer, in binary
%p	A pointer (outputs the Perl value's address in hexadecimal)
%n	This is a special formatter which stores the number of characters output so far into the next variable in the parameter list
%%	An ordinary percent sign