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Home: Perl Programming Help: Intermediate: Significance of ::_

abhinandantn New User Aug 13, 2012, 6:13 AM Post #1 of 5 (5760 views) Significance of ::_ Can't Post I came across a code where in they had used a code similar to below my $code= \@{"::_<$file"}; i understood that the above code reads each line of the $file and references each line as index and we can access each of those line as $code->[10]. what i did not get here is, what is the use of ::_ here, what is it doing to the input from the file.

BillKSmith Veteran Aug 14, 2012, 8:02 AM Post #2 of 5 (5747 views) Re: [abhinandantn] Significance of ::_ [In reply to] Can't Post This does not appear to make sense to me. Perhaps you could post a working subset of the code. I believe that the statement is creating a hard reference to an array which is referenced by a symbolic reference. (The double quotes cause $file to be interpolated into the string. The two colins at the beginning of that string say that the symbolic reference uses the main:: symbol table.) The function of the remaining characters "_>" remains a mystery. The use of 'my' is also strange. It is seldom used without 'use strict;' which would prohibit the use of symbolic reference. Good Luck, Bill

abhinandantn New User Aug 14, 2012, 8:10 AM Post #3 of 5 (5745 views) Re: [BillKSmith] Significance of ::_ [In reply to] Can't Post I saw this code in Trace.pm present in perl/lib/Devel

BillKSmith Veteran Aug 15, 2012, 6:39 AM Post #4 of 5 (5709 views) Re: [abhinandantn] Significance of ::_ [In reply to] Can't Post This code is beyond my skill level. I can safely make a few more observations. Note that the next statement is a print to STDERR. This statement clearly prints the lines described in the DESCRIPTION section of the POD in the same file. From this, we can infer that $code is a reference to an array which contains the source code of the program being debugged, $l is the number of the line being executed and $f contains the name of that program (apparently preceded by '/.'). Also note that "use strict' is not in effect. Both of these observations support my previous comments about a symbolic reference. I still cannot figure out the purpose of the special characters in the symbolic reference. Good Luck, Bill

rovf Veteran Aug 16, 2012, 12:34 AM Post #5 of 5 (5686 views) Re: [BillKSmith] Significance of ::_ [In reply to] Can't Post Though seldom used, Perl variable names can contain virtually any combination of characters (AFIK, variable names consisting of digits only are forbidden). I guess the purpose is here to create a variable with a very "unlikely" name, i.e. one which likely doesn't exist yet in the main package.

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