Learning Perl on Win32 Systems

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, ...