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File opening error. The global symbol "$ infilename" requires an explicit package name

I am writing my first perl script and am unable to compile it. I want to read in a file and output every line that matches the regex criteria for a new file. I am getting a "global symbol requires an explicit package name" error, which seems to be related to variable scope issues from what I was reading. However, I cannot figure out what happened to my code.

code:

#!/usr/bin/perl -w
use strict;
use warnings;

print "Stripping lines from data dump where WREN column is FFF\n" 

my $infilename = "./test_in.txt";
my $outfilename = "./test_out.txt";
my $in = undef;

open($in,  "<",  $infilename)  or die "Can't open $infilename: $!";
open(my $out, ">",  $outfilename) or die "Can't open $outfilename: $!";

while (<$in>) {     # assigns each line in turn to $_
   if (/.{73}FFF/){
      print $out $_;
   }
}

Error message:

syntax error at strip_nonwrites.pl line 8, near "my "
Global symbol "$infilename" requires explicit package name at strip_nonwrites.pl line 8.
Global symbol "$infilename" requires explicit package name at strip_nonwrites.pl line 12.
Global symbol "$infilename" requires explicit package name at strip_nonwrites.pl line 12.
Execution of strip_nonwrites.pl aborted due to compilation errors.
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3 answers


It is not unusual for a single syntax error to flush the parser enough to cause many false errors after the fact. This is such a case.

The first mistake is your first mistake. You are missing the semicolon at the end of line 6 ( near "my "

on line 8

).



All the "Global symbol ..." errors are just confusion created by trying to parse lines 6..8 as one command.

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You do not end the statement print

with a semicolon ;

, so it is my $infilename

considered part of this statement.



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As you read, there is print

no semicolon at the end of the first statement . Later error messages will depend on what Perl refused to do from your faulty script, and are often unreliable.

Some other points

  • You should use warnings

    give preference -w

    to the command line or the shebang line. Both are wrong at once.

  • No need for a master file ./

    for data files. This only applies when running an executable from a shell when PATH is looking for a filename if no path is specified

  • You should declare your lexical variables as late as possible in your program. In the case of file descriptors that are inside the call open

    , as you did with$out

  • The operator select

    allows you to write subsequent calls print

    without specifying a file descriptor

  • It is probably better to use substr

    or unpack

    to extract fixed position substrings from each record

This leaves a program that looks like this:

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

print "Stripping lines from data dump where WREN column is FFF\n";

my ($infilename, $outfilename) = qw/ test_in.txt test_out.txt /;

open my $in_fh,  '<',  $infilename   or die qq{Can't open "$infilename" for input: $!};
open my $out_fh, '<',  $outfilename  or die qq{Can't open "$outfilename" for output: $!};
select $out_fh;

while ( <$in_fh> ) {
   print if substr($_, 73, 3) eq 'FFF';
}
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