risk of confusion

steph_bow has asked for the wisdom of the Perl Monks concerning the following question:

Dear and Serene Monks

I would like to know if there's a possibilty of confusion between the two "$_" in my program (each $_ correponds to a line of a input file (there are two input files for my code)

My code seems to work but I would like be 100 % sure it's OK

Here is my code

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;

# la commade "use strict" permet d'être plus rigoureux

##############################################
# TASKS MADE BY THE SCRIPT 
##############################################

# the task of this script is to look for the following aircraft_id

##################################
##  ARGUMENTS OF THE SCRIPT 
##################################

#####################################
# do not forget the $ before the ARGV
#####################################


#  THE FIRST ARGUMENT :
# we have to give the name of the regulation which will help us to ope
+n the first file
# the name of the first file to open is :  Regulation_Slot_List_${reg_
+id}
 my ${reg_id} = "$ARGV[0]";

 # THE SECOND ARGUMENT
 #  it will be used later to open the ALL_FT file
 my $date = "$ARGV[1]";


################# END OF THE DECLARATION OF THE ARGUMENTS

#################  IN WHICH DIRECTORY WE ARE ########################

my $Current_Dir = `pwd`;
print STDOUT "the current directory is $Current_Dir";

#####################################################################



################### OPEN THE ANALYSIS INFILE #########################
+###
# open the first file 
# do not forget the "" to declare  my ${analysis_file} = 

my ${analysis_file} = "without_commas_Analysis_Regulation_Slot_List_${
+reg_id}_last.csv";
open(INFILE,"<${analysis_file}") or die "Can't open ${analysis_file} :
+ $!";
######################################################################
+#####


################### OPEN THE OUTFILE ############################
# open the first file 
# do not forget the "" to declare  my ${analysis_file} = 

my $outfile = "with_ALL_FT_${analysis_file}";

open(OUTFILE,">${outfile}") or die "Can't open ${outfile} : $!";
######################################################################
+#####



# we want to skip the first line of the INFILE

    while (<INFILE>){
    # the /^ indicates the begining of the research for $_ ($_ is unde
+rstated here)
    my @Elements = split(/;/,$_); 

    # $Elements[2] is the $CTO

    my $aircraft_id = $Elements[1];
    

        if ($Elements[4] ne ""){
        # print STDOUT "$Elements[4]";
        ################### OPEN THE ALL_FT FILE #####################
+#######
        # open the first file 
        # do not forget the "" to declare  my ${ALL_FT_file} = 

        my ${ALL_FT_file} = "ALL_FT.${date}";
        open(INFILE_2,"<${ALL_FT_file}") or die "Can't open ${ALL_FT_f
+ile} : $!";
        ##############################################################
+#############
        

            while(<INFILE_2>){
            my $Line_ALL_FT = $_;
            print STDOUT "$Line_ALL_FT\n";
            my @Parts_ALL_FT = split(/;/,$Line_ALL_FT);
            my $aircraft_ALL_FT_id = $Parts_ALL_FT[2]; 
            # print STDOUT "le nom de l'avion dans le fichier ALL_FT e
+st $aircraft_ALL_FT_id\n";
            # print STDOUT "le nom de l'avion dans le fichier analysis
+ est $aircraft_id\n";
            next if ($aircraft_id ne $aircraft_ALL_FT_id);
                if ($aircraft_id eq $aircraft_ALL_FT_id){

                # do not forget the "" in the declaration of the OUTFI
+LE
                
                print OUTFILE "$aircraft_id\n";
            
                }    

            }
        close INFILE_2;
        }
    } 


close INFILE;
close OUTFILE;
[download]

Here is my first input file : the analysis file (the true one, the one I opened with wordpad)

08:47:46;;;;;
08:48:45;;;;;
08:49:43;DAL11;08:47;527;08:50;530;3
08:50:41;;;;;
08:51:40;;;;;
12:16:28;RYR211;12:13;733;12:16;736;3
12:17:26;EEZ95A;12:23;743;12:17;737;-6
12:18:24;SHT2938;12:24;744;12:17;737;-7
[download]

Here is my second input file : the ALL_FT file

LIRF;KJFK;EEZ95A;
EGKK;KATL;DAL11;
ENCN;EHAM;KLM1210;
LEMD;LIMC;AZA067;
[download]

Here is my output file

DAL11
EEZ95A
[download]

Comment on risk of confusion Select or Download Code

Replies are listed 'Best First'.
Re: risk of confusion by shmem (Chancellor) on Aug 07, 2007 at 16:07 UTC
So the relevant parts of your code are, along with the question: `my $analysis_file = shift; open INFILE_1, '<', $analysis_file or die "Can't open '$analysis_file': $!\n"; while(<INFILE_1>) { my $ALL_FT_FILE = $_; # or some part of $_ after munging open INFILE_2, '<', $ALL_FT_FILE or die "Can't open '$ALL_FT_FILE': $!\n"; while(<INFILE_2>) { ... # is the outer $_ clobbered here? } }` [download] That's considerably shorter, and more to the point, isn't it? Answer: ~~No, each `$_` is localized to its own while() block. But you can't access the contents of the outer `$_` from the inner block, unless you assign that to another variable.~~ <update> Sigh. As jdporter pointed out, yes, `$_` isn't localized in a `while` loop: `open O, '>', 'foo'; print O "bar\n"; close O; open O, '>', 'bar'; print O "$_\n" for qw(foo quux wrdlbrmfd); close O; open I, '<', 'foo'; while (<I>) { chop; open II, '<', $_ if -f $_; while (<II>) { print; } print "\$_ = '$_'\n"; } __END__ foo quux wrdlbrmfd $_ = ''` [download] As you see at the last line of the ouput above, `$_` is clobbered. </update> Some nits: three argument open is generally preferred (there are edge cases where 2-argument open makes sense) the construct `"${ALL_FT_FILE}"`is only used to disambiguate an interpolated variable from an adjacent literal, as in `"${foo}_bar"`; interpolating a single variable in a double quoted string is bad practice, unless it is necessary - in your code it is not code inside a block is better readable if it's indented relative to its enclosing brackets </pedantic> :) --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^2: risk of confusion by jdporter (Paladin) on Aug 07, 2007 at 18:56 UTC
each $_ is localized to its own while() block. I'm sorry, that is false. Are you getting while confused with foreach? As it says in When to Still Use local(): it's important to localize $_ in any routine that assigns to it. Look out for implicit assignments in `while` conditionals. So the correct answer to the OP is actually Yes, there will be "confusion". local can be used to remedy the problem. A word spoken in Mind will reach its own level, in the objective world, by its own weight	[reply] [d/l]
Re^3: risk of confusion by shmem (Chancellor) on Aug 07, 2007 at 21:53 UTC
Are you getting while confused with foreach? Obviously. Thanks for the correction. I'm very sorry about having propagated crap blush... maybe the corrections do mend that. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply]
Re: risk of confusion by thezip (Vicar) on Aug 07, 2007 at 16:04 UTC
steph_bow, If you're concerned that that the $_ variable is going to get clobbered, try reading/assigning each line into a variable, as in: `while (my $file_1_line = <INFILE>) { ... do stuff }` [download] BTW, your code would be much more readable (to Perlmonks) if you only included the relevant code that demonstrates your particular issue. You might consider weeding it down to about 10-15 lines, with not so many comments, as they don't aid in increasing my understanding of the problem at hand. Update: Added a number to the variable name Where do you want them* to go today?*	[reply] [d/l]