Parsing of blocks (e.g. foo { bar })

[Tor Houghton]

Hi,

I'm wondering if there is a more elegant way of parsing "blocks" of data.

I have a configuration file, thus:

# comment

some.host.name {
; another comment
/etc/hostname.fxp0
/etc/hosts
/etc/mail
}

And I currently parse this using the following code:

while(<CONF>) {
next if(/^\s*(\#||^\s*$/);
if(m#(\S+)\s+{# .. m#}#) {
$HOST=$1 if $1;
if(!/\{|\}/) {
print "add: $HOST ",$_;
}
}
}

Before I go "all out" and complete this section of the code using the
above technique, I was wondering if there was other (better) ways of doing
this (for one, I'm not sure how to catch out any errors in the file, for
instance:

some.host.here {
another.host {
/usr
/opt
}
/etc
/var/mail
}

... here the current code fails miserably. Mind you, I'm probably the only
one going to use this, so that may not be such a big deal :-> )

Thanks!

Tor

 

[Brian Harnish]

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Hash: SHA1

Hi,

I'm wondering if there is a more elegant way of parsing "blocks" of data. [snip]
Before I go "all out" and complete this section of the code using the
above technique, I was wondering if there was other (better) ways of doing
this (for one, I'm not sure how to catch out any errors in the file, for
instance:

some.host.here {
another.host {
/usr
/opt
}
/etc
/var/mail
}

.. here the current code fails miserably. Mind you, I'm probably the only
one going to use this, so that may not be such a big deal :-> )

You didn't really say how you wanted to handle this condition. Is it a
valid condition, or can your program just abort?

If you need to handle that condition, then instead of using the scalar
".."'s flag, use a nesting counter:
my $nest = 0;
while(<CONF>) {
$nest++ if (/(\S+)\s*\{/);
$nest-- if (/\}/);
if($nest == 1) { # Or, $nest >= 1
# Handle conditions.
}
}

Actually, thinking about it, aborting would use very similar logic.

- Brian
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[Tor Houghton]

[snip]

You didn't really say how you wanted to handle this condition. Is it a
valid condition, or can your program just abort?

Hm. No, it's an invalid condition, so the program should just abort.

If you need to handle that condition, then instead of using the scalar
".."'s flag, use a nesting counter:
my $nest = 0;
while(<CONF>) {
$nest++ if (/(\S+)\s*\{/);
$nest-- if (/\}/);
if($nest == 1) { # Or, $nest >= 1
# Handle conditions.
}
}

Actually, thinking about it, aborting would use very similar logic.

Ah. I didn't think about doing it that way. Thanks!

Tor

 

[David K. Wall]

I'm wondering if there is a more elegant way of parsing "blocks"
of data.
[snip]

Before I go "all out" and complete this section of the code using
the above technique, I was wondering if there was other (better)
ways of doing this

If you're not tied to that particular format you could use
Config::Simple or one of the numerous other Config::* modules in the
CPAN.

But I may be revealing some ignorance here; your data may be the
output of another program that requires that format.

 

[Tor Houghton]

If you're not tied to that particular format you could use
Config::Simple or one of the numerous other Config::* modules in the
CPAN.

Thanks for the tip!

For this application, however, I need to make sure it'll work on a system
"out of the box", without the worry of whether a certain CPAN module needs
to be installed.

Tor