Festival Speech Synthesis System: - Speech Resource Pages

25. Tools
A number of basic data manipulation tools are supported by Festival. These often make building new modules very
easy and are already used in many of the existing modules. They typically offer a Scheme method for entering data,
and Scheme and C++ functions for evaluating it.
25.1 Regular expressions
25.2 CART trees Building and using CART
25.3 Ngrams Building and using Ngrams
25.4 Viterbi decoder Using the Viterbi decoder
25.5 Linear regression Building and using linear regression models
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25.1 Regular expressions
Regular expressions are a formal method for describing a certain class of mathematical languages. They may be
viewed as patterns which match some set of strings. They are very common in many software tools such as scripting
languages like the UNIX shell, PERL, awk, Emacs etc. Unfortunately the exact form of regualr expressions often
differs slightly between different applications making their use often a little tricky.
Festival support regular expressions based mainly of the form used in the GNU libg++ Regex class, though we have
our own implementation of it. Our implementation (EST_Regex) is actually based on Henry Spencer's
`regex.c' as distributed with BSD 4.4.
Regular expressions are represented as character strings which are interpreted as regular expressions by certain
Scheme and C++ functions. Most characters in a regular expression are treated as literals and match only that
character but a number of others have special meaning. Some characters may be escaped with preceeding backslashes
to change them from operators to literals (or sometime literals to operators).
.
Matches any character.
$
matches end of string
^
matches beginning of string
X*
matches zero or more occurrences of X, X may be a character, range of parenthesized expression.
X+
matches one or more occurrences of X, X may be a character, range of parenthesized expression.
X?
matches zero or one occurrence of X, X may be a character, range of parenthesized expression.
[...]
a ranges matches an of the values in the brackets. The range operator "-" allows specification of ranges e.g. az
for all lower case characters. If the first character of the range is ^ then it matches anything character except
those specificed in the range. If you wish - to be in the range you must put that first.
\\(...\\)
Treat contents of parentheses as single object allowing operators *, +, ? etc to operate on more than single
characters.
X\\|Y
matches either X or Y. X or Y may be single characters, ranges or parenthesized expressions.
Note that actuall only one backslash is needed before a character to escape it but becuase these expressions are most
often contained with Scheme or C++ strings, the escpae mechanaism for those strings requires that backslash itself be
escaped, hence you will most often be required to type two backslashes.