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The interface to file handles that are linked to variables with
Perl's tie( ) function is not yet complete. The
format( ) and write( )
functions are missing. If you configure Perl with sfio,
write( ) and format( )
should work just fine.
Instead of format( ), you can use
printf( ). For example, the following formats are
equivalent:
format printf---------------##.## %2.2f####.## %4.2f
To print a string with fixed-length elements, use the printf(
) format %n.ms where n
is the length of the field allocated for the string and m
is the maximum number of characters to take from the string. For example:
printf "[%5.3s][%10.10s][%30.30s]\n",12345, "John Doe", "1234 Abbey Road"
prints:
[ 123][ John Doe][ 1234 Abbey Road]
Notice that the first string was allocated five characters in
the output, but only three were used because m=5 and
n=3 (%5.3s). If you want
to ensure that the text will always be correctly aligned without being truncated,
n should always be greater than or equal to m.
You can change the alignment to the left by adding a minus sign
(-) after the %. For
example:
printf "[%-5.5s][%-10.10s][%-30.30s]\n",123, "John Doe", "1234 Abbey Road"
prints:
[123 ][John Doe ][1234 Abbey Road ]
You can also use a plus sign (+)
for the right-side alignment. For example:
printf "[%+5s][%+10s][%+30s]\n",123, "John Doe", "1234 Abbey Road"
prints:
[ 123][ John Doe][ 1234 Abbey Road]
Another alternative to format( )
and printf( ) is to use the Text::Reform
module from CPAN.
In the examples above we've printed the number 123
as a string (because we used the %s format specifier),
but numbers can also be printed using numeric formats. See perldoc
-f sprintf for full details.
The output of system( ), exec(
), and open(PIPE,"|program") calls
will not be sent to the browser unless Perl was configured with sfio.
To learn if your version of Perl is sfio-enabled,
look at the output of the perl -V command for the
useperlio and d_sfio strings.
You can use backticks as a possible workaround:
print `command here`;
But this technique has very poor performance, since it forks a new process. See the discussion about forking in Chapter 10.
Perl executes BEGIN blocks as soon
as possible, when it's compiling the code. The same is true under mod_perl.
However, since mod_perl normally compiles scripts and modules only once, either
in the parent process or just once per child, BEGIN
blocks are run only once. As the perlmod manpage explains,
once a BEGIN block has run, it is immediately undefined.
In the mod_perl environment, this means that BEGIN
blocks will not be run during the response to an incoming request unless that
request happens to be the one that causes the compilation of the code. However,
there are cases when BEGIN blocks will be rerun
for each request.
BEGIN blocks in modules and files
pulled in via require( ) or use(
) will be executed:
Apache::StatINC.
PerlFreshRestart is On.
BEGIN
block is deleted from %INC, before the module's
compilation is needed. The same thing happens when do(
) is used, which loads the module even if it's already loaded.
BEGIN blocks in Apache::Registry
scripts will be executed:
Apache::RegistryLoader.
Apache::RegistryLoader
and PerlFreshRestart is On.
Note that this second list is applicable only to the scripts themselves. For the modules used by the scripts, the previous list applies.
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Created: March 27, 2003
Revised: July 23, 2003
URL: http://webreference.com/programming/perl/mod_perl/chap6/2
