Transliteration
When you
want to take a string and replace every instance of some character
with some new character, or delete every instance of some character,
you can do so with carefully selected s///
commands. But suppose you had to change all of the
a
’s into b
’s, and
all of the b
’s into
a
’s? You can’t do that with two
s///
commands because the second one would undo
all of the changes that the first one made.
Perl provides a
tr
operator that does the trick:
tr/ab/ba/;
The tr
operator takes two arguments: an
old string and a new
string. These arguments work like the two arguments to
s///
; in other words, there’s some
delimiter
that appears immediately after the tr
keyword that
separates and terminates the two arguments (in this case, a slash,
but nearly any character will do).
The tr
operator modifies the contents of the
$_
variable (just
like s///
), looking for characters of the old
string within the $_
variable. All such characters
found are replaced with the corresponding characters in the new
string. Here are some examples:
$_ = "fred and barney"; tr/fb/bf/; # $_ is now "bred and farney" tr/abcde/ABCDE/; # $_ is now "BrED AnD fArnEy" tr/a-z/A-Z/; # $_ is now "BRED AND FARNEY"
Notice how a range of characters can be indicated by two characters separated by a dash. If you need a literal dash in either string, precede it with a backslash.
If the new string is shorter than the old string, the last character of the new string is repeated enough times to make the strings equal length, ...
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