Note that this is not guaranteed to contribute to the readability of
your program.
-=head2 Assigment Operators
+=head2 Assignment Operators
"=" is the ordinary assignment operator.
In a list context, it's just the list argument separator, and inserts
both its arguments into the list.
-The => digraph is simply a synonym for the comma operator. It's useful
-for documenting arguments that come in pairs.
+The => digraph is mostly just a synonym for the comma operator. It's useful for
+documenting arguments that come in pairs. As of 5.001, it also forces
+any word to the left of it to be interpreted as a string.
=head2 List Operators (Rightward)
C</o> constitutes a promise that you won't change the variables in the pattern.
If you change them, Perl won't even notice.
-If the PATTERN evaluates to a null string, the most recently executed
-(and successfully compiled) regular expression is used instead.
+If the PATTERN evaluates to a null string, the last
+successfully executed regular expression is used instead.
If used in a context that requires a list value, a pattern match returns a
list consisting of the subexpressions matched by the parentheses in the
end-of-string test, the variable will be interpolated into the pattern
at run-time. If you only want the pattern compiled once the first time
the variable is interpolated, use the C</o> option. If the pattern
-evaluates to a null string, the most recently executed (and successfully compiled) regular
+evaluates to a null string, the last successfully executed regular
expression is used instead. See L<perlre> for further explanation on these.
Options are:
# Delete C comments.
$program =~ s {
- /\* (?# Match the opening delimiter.)
- .*? (?# Match a minimal number of characters.)
- \*/ (?# Match the closing delimiter.)
+ /\* # Match the opening delimiter.
+ .*? # Match a minimal number of characters.
+ \*/ # Match the closing delimiter.
} []gsx;
s/^\s*(.*?)\s*$/$1/; # trim white space
variable (e.g. <$foo>), then that variable contains the name of the
filehandle to input from.
-If the string inside angle brackets is not a filehandle, it is
-interpreted as a filename pattern to be globbed, and either a list of
-filenames or the next filename in the list is returned, depending on
-context. One level of $ interpretation is done first, but you can't
-say C<E<lt>$fooE<gt>> because that's an indirect filehandle as explained in the
-previous paragraph. You could insert curly brackets to force
-interpretation as a filename glob: C<E<lt>${foo}E<gt>>. (Alternately, you can
-call the internal function directly as C<glob($foo)>, which is probably
-the right way to have done it in the first place.) Example:
+If the string inside angle brackets is not a filehandle, it is interpreted
+as a filename pattern to be globbed, and either a list of filenames or the
+next filename in the list is returned, depending on context. One level of
+$ interpretation is done first, but you can't say C<E<lt>$fooE<gt>>
+because that's an indirect filehandle as explained in the previous
+paragraph. In older version of Perl, programmers would insert curly
+brackets to force interpretation as a filename glob: C<E<lt>${foo}E<gt>>.
+These days, it's consdired cleaner to call the internal function directly
+as C<glob($foo)>, which is probably the right way to have done it in the
+first place.) Example:
while (<*.c>) {
chmod 0644, $_;
implementation of using a shell, the glob() routine may get "Arg list too
long" errors (unless you've installed tcsh(1L) as F</bin/csh>).
+A glob only evaluates its (embedded) argument when it is starting a new
+list. All values must be read before it will start over. In a list
+context this isn't important, because you automatically get them all
+anyway. In a scalar context, however, the operator returns the next value
+each time it is called, or a FALSE value if you've just run out. Again,
+FALSE is returned only once. So if you're expecting a single value from
+a glob, it is much better to say
+
+ ($file) = <blurch*>;
+
+than
+
+ $file = <blurch*>;
+
+because the latter will alternate between returning a filename and
+returning FALSE.
+
+It you're trying to do variable interpolation, it's definitely better
+to use the glob() function, because the older notation can cause people
+to become confused with the indirect filehandle notatin.
+
+ @files = glob("$dir/*.[ch]");
+ @files = glob($files[$i]);
+
=head2 Constant Folding
Like C, Perl does a certain amount of expression evaluation at
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