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how to deal with incorrect command line argument

by scripter87 (Novice)
on Oct 30, 2013 at 21:35 UTC ( #1060452=perlquestion: print w/replies, xml ) Need Help??

scripter87 has asked for the wisdom of the Perl Monks concerning the following question:

Hey monks, Got an issue that I would like help with if possible. I got this program that accepts arguments from the cl so say I typed perl test.html testb.html the program would do something with the arguments. The problem I have is that if I typed the arguments incorrectly say perl twst.html testb.html (they should both be as above) I want the program to report an error "warn" but continue and work with the correct argument. This is a snippet that I cant correctly use
foreach $_(@ARGV) { my $rename = $_; if (!-e $rename) { warn "$rename does not exist"; # previously I had this as die but +obviously that killed the program and did not continue with the corre +ct argument for(my $i=0;$i<$rename;$i++){ # I am not really sure if this loop +is the right idea #or what to put in it.. }

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Re: how to deal with incorrect command line argument
by Kenosis (Priest) on Oct 30, 2013 at 21:58 UTC

    Perhaps the following will be helpful:

    use strict; use warnings; my @array; for (@ARGV) { if (-e) { push @array, $_; next; } warn qq{"$_" doesn't exist!}; } @ARGV = @array; print "@ARGV";

    This pushes the 'good' params onto @array and warns on the others, then reinitializes @ARGV with the 'good' ones.

      Slightly simplified, I think:

      use strict; use warnings; for (@ARGV) { if (-e) { &doTheWork($_); } else { warn qq{"$_" doesn't exist!}; } }

        Good suggestion! Or even just:

        use strict; use warnings; (-e) ? doTheWork($_) : warn qq{"$_" doesn't exist!} for @ARGV;
      Thanks my man, does the trick. May I ask a few questions on your solution though... I am going to comment it on your code and maybe you can correct me where I am wrong.
      my @array; # this an array to store the good arguments for (@ARGV) { # for the argumets array if (-e) { # if the file exists push @array, $_;# push the file that exists onto the @array # why use $_ here? next; # what purpose has this } warn qq{"$_" doesn't exist!}; } @ARGV = @array;
      I Appreciate the time you took to answer my question to man.

        You're most welcome! Am glad it helped.

        You're commenting is correct. You asked, "why use $_ here?" Because Perls default scalar ($_) is implicitly used in the for loop that's iterating through the elements of @ARGV. Note, also, that Perl's default scalar is also implicitly used in the expression if (-e) { as that expression is equivalent to if (-e $_) {.

        The purpose of next is to get the next element of @ARGV, otherwise a warn would occur.

Re: how to deal with incorrect command line argument
by AnomalousMonk (Bishop) on Oct 31, 2013 at 08:10 UTC
    ... I want the program to report an error "warn" but continue and work with the correct argument.

    In general, I find I have enough trouble when I try to guess what my programs should be doing; I certainly don't want my programs making those guesses!

    However, in the spirit of giving good advice and then immediately undercutting it, you might look at Text::Levenshtein and related fuzzy string comparison modules; see Levenshtein distance. The strategy might be something like "look for all file names in a given directory with an L-D (or other match metric) less than a given threshold, then use the file name with the least distance if that name is unique".

    >perl -wMstrict -le "use Text::LevenshteinXS; ;; my $tyop = 'twst.html'; for my $try (qw(test.html testb.html)) { my $d = distance($tyop, $try); print qq{'$tyop' < $d > '$try'}; } " 'twst.html' < 1 > 'test.html' 'twst.html' < 2 > 'testb.html'
      <speechless> </speechless>
      Um. Wow. I have some self-educational opportunities here, it seems.

        Make sure to have paramedics standing by before you start juggling your swiss army chainsaws like this :).

      The day that commands in the rm family start exposing that kind of behaviour, where not only they offer suggestions a la Google ("twst.htm doesn't exist - did you mean to rm test.htm instead?") but also assume that that's what I meant ("twst.htm doesn't exist, so I went out of my way for you and rm'ed test.html instead, which, hey, you only worked on for 8 hours straight and haven't backed up yet. You're welcome, bro.") I swear I'm never touching a computer again.

        ROFLSHIPMP OMG My wife is going to disown me I am laughing so hard.

        Nice way to end my PerlMonks day. Thank you!

Re: how to deal with incorrect command line argument
by Anonymous Monk on Oct 30, 2013 at 23:08 UTC

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