[log4perl-devel] Log::Log4perl Recipe of the Week (#19)

[<log...@pe...>]

Welcome to the Log::Log4perl recipe of the week. Today:

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Log::Log4perl Recipe of the Week (#19):

Log4perl doesn't interpret my backslashes correctly!
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If you're using Log4perl's feature to specify the
configuration as a string in your program (as opposed to a
separate configuration file), chances are that you've
written it like this:

    # *** WRONG! ***

    Log::Log4perl->init( \ <<END_HERE);
        log4perl.logger = WARN, A1
        log4perl.appender.A1 = Log::Dispatch::Screen
        log4perl.appender.A1.layout = \
            Log::Log4perl::Layout::PatternLayout
        log4perl.appender.A1.layout.ConversionPattern = %m%n
    END_HERE

    # *** WRONG! ***

and you're getting the following error message:

    Layout not specified for appender A1 at .../Config.pm line 342.

What's wrong? The problem is that you're using a
here-document with substitution enabled ("<<END_HERE") and
that Perl won't interpret backslashes at line-ends as
continuation characters but will essentially throw them out.
So, in the code above, the layout line will look like

    log4perl.appender.A1.layout =

to Log::Log4perl which causes it to report an error. To
interpret the backslash at the end of the line correctly as
a line-continuation character, use the non-interpreting mode
of the here-document like in

    # *** RIGHT! ***

    Log::Log4perl->init( \ <<'END_HERE');
        log4perl.logger = WARN, A1
        log4perl.appender.A1 = Log::Dispatch::Screen
        log4perl.appender.A1.layout = \
            Log::Log4perl::Layout::PatternLayout
        log4perl.appender.A1.layout.ConversionPattern = %m%n
    END_HERE

    # *** RIGHT! ***

(note the single quotes around 'END_HERE') or use "q{...}"
instead of a here-document and Perl will treat the
backslashes at line-end as intended.


Have fun! Until next week.

-- Mike

###################################
# Mike Schilli                    #
# log...@pe...        #
# http://perlmeister.com          #
# http://log4perl.sourceforge.net #
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