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Re: My first perl script is working, what did I do wrong?

by eyepopslikeamosquito (Canon)
on Nov 09, 2012 at 07:13 UTC ( #1003075=note: print w/ replies, xml ) Need Help??


in reply to My first perl script is working, what did I do wrong?

Some suggestions below on how to improve the early part of your script.

1) Replace:

if ($#ARGV != 0) { print "One, and only one (not $#ARGV), command line parameter is +expected\n"; exit; }
with:
@ARGV == 1 or die "usage: $0 inputfile\n";
When a script encounters an error it should exit with a non-zero value (a bald exit returns a zero exit value), a usage statement is conventional, and or die is idiomatic.

BTW, you should rarely need to use the cumbersome $#array notation. Using it here is unnecessary and the code is clearer using @ARGV instead. Another example, from Perl Best Practices, chapter 5, "Use negative indices when counting from the end of an array" is to prefer $frames[-2] to $frames[$#frames-1] because it is easier on the eye and avoids the undesirable repetition of the variable name (DRY).

2) Replace:

my $inputFile=$ARGV[0];
with:
my $inputFile = shift;
Using shift makes maintenance easier if you later add or remove command line arguments because you don't need to manually shuffle the ARGV indices (which are "magic numbers").

3) Replace:

if ( not -e $inputFile) { die "$inputFile doesn't exist!!!\nExiting.\n"; }
with:
-f $inputFile or die "input file '$inputFile' does not exist.\n";
Using -f is more precise than -e because the first argument must be a file (not a directory, say). Using or die is idiomatic and more concise.

4) Replace:

open my $file, $inputFile or die "Could not open $inputFile: $!";
with:
open my $file, '<', $inputFile or die "Could not open $inputFile: $!";
As for why the three-argument form of open is preferred, the old two-argument form of open is subject to various security exploits as described at Opening files securely in Perl.


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