OMG any one know about PERL scripting HELP....?

Answers

1. kartoos5050

   On 2006-08-14 23:47:32

   
   
   The only kind of simple statement is an expression evaluated for its side effects. Every simple statement must be terminated with a semicolon, unless it is the final statement in a block, in which case the semicolon is optional. (A semicolon is still encouraged there if the block takes up more than one line, because you may eventually add another line.) Note that there are some operators like eval {} and do {} that look like compound statements, but aren't (they're just TERMs in an expression), and thus need an explicit termination if used as the last item in a statement. Any simple statement may optionally be followed by a SINGLE modifier, just before the terminating semicolon (or block ending). The possible modifiers are: if EXPR unless EXPR while EXPR until EXPR foreach EXPR The if and unless modifiers have the expected semantics, presuming you're a speaker of English. The foreach modifier is an iterator: For each value in EXPR, it aliases $_ to the value and executes the statement. The while and until modifiers have the usual ``while loop'' semantics (conditional evaluated first), except when applied to a do -BLOCK (or to the now-deprecated do -SUBROUTINE statement), in which case the block executes once before the conditional is evaluated. This is so that you can write loops like: do { $line = ; ... } until $line eq ".\n"; See do. Note also that the loop control statements described later will NOT work in this construct, because modifiers don't take loop labels. Sorry. You can always put another block inside of it (for next) or around it (for last) to do that sort of thing. For next, just double the braces: do {{ next if $x == $y; # do something here }} until $x++ > $z; For last, you have to be more elaborate: LOOP: { do { last if $x = $y**2; # do something here } while $x++ <= $z; } -------------------------------------------------------------------------------- Compound statements In Perl, a sequence of statements that defines a scope is called a block. Sometimes a block is delimited by the file containing it (in the case of a required file, or the program as a whole), and sometimes a block is delimited by the extent of a string (in the case of an eval). But generally, a block is delimited by curly brackets, also known as braces. We will call this syntactic construct a BLOCK. The following compound statements may be used to control flow: if (EXPR) BLOCK if (EXPR) BLOCK else BLOCK if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK LABEL while (EXPR) BLOCK LABEL while (EXPR) BLOCK continue BLOCK LABEL for (EXPR; EXPR; EXPR) BLOCK LABEL foreach VAR (LIST) BLOCK LABEL BLOCK continue BLOCK Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not statements. This means that the curly brackets are required--no dangling statements allowed. If you want to write conditionals without curly brackets there are several other ways to do it. The following all do the same thing: if (!open(FOO)) { die "Can't open $FOO: $!"; } die "Can't open $FOO: $!" unless open(FOO); open(FOO) or die "Can't open $FOO: $!"; # FOO or bust! open(FOO) ? 'hi mom' : die "Can't open $FOO: $!"; # a bit exotic, that last one The if statement is straightforward. Because BLOCKs are always bounded by curly brackets, there is never any ambiguity about which if an else goes with. If you use unless in place of if, the sense of the test is reversed. The while statement executes the block as long as the expression is true (does not evaluate to the null string ("") or 0 or "0"). The LABEL is optional, and if present, consists of an identifier followed by a colon. The LABEL identifies the loop for the loop control statements next, last, and redo. If the LABEL is omitted, the loop control statement refers to the innermost enclosing loop. This may include dynamically looking back your call-stack at run time to find the LABEL. Such desperate behavior triggers a warning if you use the -w flag. If there is a continue BLOCK, it is always executed just before the conditional is about to be evaluated again, just like the third part of a for loop in C. Thus it can be used to increment a loop variable, even when the loop has been continued via the next statement (which is similar to the C continue statement). -------------------------------------------------------------------------------- Loop Control The next command is like the continue statement in C; it starts the next iteration of the loop: LINE: while () { next LINE if /^#/; # discard comments ... } The last command is like the break statement in C (as used in loops); it immediately exits the loop in question. The continue block, if any, is not executed: LINE: while () { last LINE if /^$/; # exit when done with header ... } The redo command restarts the loop block without evaluating the conditional again. The continue block, if any, is not executed. This command is normally used by programs that want to lie to themselves about what was just input. For example, when processing a file like /etc/termcap. If your input lines might end in backslashes to indicate continuation, you want to skip ahead and get the next record. while (<>) { chomp; if (s/\\$//) { $_ .= <>; redo unless eof(); } # now process $_ } which is Perl short-hand for the more explicitly written version: LINE: while (defined($line = )) { chomp($line); if ($line =~ s/\\$//) { $line .= ; redo LINE unless eof(); # not eof(ARGV)! } # now process $line } Note that if there were a continue block on the above code, it would get executed even on discarded lines. This is often used to reset line counters or ?pat? one-time matches. # inspired by :1,$g/fred/s//WILMA/ while (<>) { ?(fred)? && s//WILMA $1 WILMA/; ?(barney)? && s//BETTY $1 BETTY/; ?(homer)? && s//MARGE $1 MARGE/; } continue { print "$ARGV $.: $_"; close ARGV if eof(); # reset $. reset if eof(); # reset ?pat? } If the word while is replaced by the word until, the sense of the test is reversed, but the conditional is still tested before the first iteration. The loop control statements don't work in an if or unless, since they aren't loops. You can double the braces to make them such, though. if (/pattern/) {{ next if /fred/; next if /barney/; # so something here }} The form while/if BLOCK BLOCK, available in Perl 4, is no longer available. Replace any occurrence of if BLOCK by if (do BLOCK). -------------------------------------------------------------------------------- For Loops Perl's C-style for loop works exactly like the corresponding while loop; that means that this: for ($i = 1; $i < 10; $i++) { ... } is the same as this: $i = 1; while ($i < 10) { ... } continue { $i++; } (There is one minor difference: The first form implies a lexical scope for variables declared with my in the initialization expression.) Besides the normal array index looping, for can lend itself to many other interesting applications. Here's one that avoids the problem you get into if you explicitly test for end-of-file on an interactive file descriptor causing your program to appear to hang. $on_a_tty = -t STDIN && -t STDOUT; sub prompt { print "yes? " if $on_a_tty } for ( prompt(); ; prompt() ) { # do something } -------------------------------------------------------------------------------- Foreach Loops The foreach loop iterates over a normal list value and sets the variable VAR to be each element of the list in turn. If the variable is preceded with the keyword my, then it is lexically scoped, and is therefore visible only within the loop. Otherwise, the variable is implicitly local to the loop and regains its former value upon exiting the loop. If the variable was previously declared with my, it uses that variable instead of the global one, but it's still localized to the loop. (Note that a lexically scoped variable can cause problems if you have subroutine or format declarations within the loop which refer to it.) The foreach keyword is actually a synonym for the for keyword, so you can use foreach for readability or for for brevity. (Or because the Bourne shell is more familiar to you than csh, so writing for comes more naturally.) If VAR is omitted, $_ is set to each value. If any element of LIST is an lvalue, you can modify it by modifying VAR inside the loop. That's because the foreach loop index variable is an implicit alias for each item in the list that you're looping over. If any part of LIST is an array, foreach will get very confused if you add or remove elements within the loop body, for example with splice. So don't do that. foreach probably won't do what you expect if VAR is a tied or other special variable. Don't do that either. Examples: for (@ary) { s/foo/bar/ } foreach my $elem (@elements) { $elem *= 2; } for $count (10,9,8,7,6,5,4,3,2,1,'BOOM') { print $count, "\n"; sleep(1); } for (1..15) { print "Merry Christmas\n"; } foreach $item (split(/:[\\\n:]*/, $ENV{TERMCAP})) { print "Item: $item\n"; } Here's how a C programmer might code up a particular algorithm in Perl: for (my $i = 0; $i < @ary1; $i++) { for (my $j = 0; $j < @ary2; $j++) { if ($ary1[$i] > $ary2[$j]) { last; # can't go to outer :-( } $ary1[$i] += $ary2[$j]; } # this is where that last takes me } Whereas here's how a Perl programmer more comfortable with the idiom might do it: OUTER: foreach my $wid (@ary1) { INNER: foreach my $jet (@ary2) { next OUTER if $wid > $jet; $wid += $jet; } } See how much easier this is? It's cleaner, safer, and faster. It's cleaner because it's less noisy. It's safer because if code gets added between the inner and outer loops later on, the new code won't be accidentally executed. The next explicitly iterates the other loop rather than merely terminating the inner one. And it's faster because Perl executes a foreach statement more rapidly than it would the equivalent for loop. -------------------------------------------------------------------------------- Basic BLOCKs and Switch Statements A BLOCK by itself (labeled or not) is semantically equivalent to a loop that executes once. Thus you can use any of the loop control statements in it to leave or restart the block. (Note that this is NOT true in eval{}, sub{}, or contrary to popular belief do{} blocks, which do NOT count as loops.) The continue block is optional. The BLOCK construct is particularly nice for doing case structures. SWITCH: { if (/^abc/) { $abc = 1; last SWITCH; } if (/^def/) { $def = 1; last SWITCH; } if (/^xyz/) { $xyz = 1; last SWITCH; } $nothing = 1; } There is no official switch statement in Perl, because there are already several ways to write the equivalent. In addition to the above, you could write SWITCH: { $abc = 1, last SWITCH if /^abc/; $def = 1, last SWITCH if /^def/; $xyz = 1, last SWITCH if /^xyz/; $nothing = 1; } (That's actually not as strange as it looks once you realize that you can use loop control ``operators'' within an expression, That's just the normal C comma operator.) or SWITCH: { /^abc/ && do { $abc = 1; last SWITCH; }; /^def/ && do { $def = 1; last SWITCH; }; /^xyz/ && do { $xyz = 1; last SWITCH; }; $nothing = 1; } or formatted so it stands out more as a ``proper'' switch statement: SWITCH: { /^abc/ && do { $abc = 1; last SWITCH; }; /^def/ && do { $def = 1; last SWITCH; }; /^xyz/ && do { $xyz = 1; last SWITCH; }; $nothing = 1; } or SWITCH: { /^abc/ and $abc = 1, last SWITCH; /^def/ and $def = 1, last SWITCH; /^xyz/ and $xyz = 1, last SWITCH; $nothing = 1; } or even, horrors, if (/^abc/) { $abc = 1 } elsif (/^def/) { $def = 1 } elsif (/^xyz/) { $xyz = 1 } else { $nothing = 1 } A common idiom for a switch statement is to use foreach's aliasing to make a temporary assignment to $_ for convenient matching: SWITCH: for ($where) { /In Card Names/ && do { push @flags, '-e'; last; }; /Anywhere/ && do { push @flags, '-h'; last; }; /In Rulings/ && do { last; }; die "unknown value for form variable where: `$where'"; } Another interesting approach to a switch statement is arrange for a do block to return the proper value: $amode = do { if ($flag & O_RDONLY) { "r" } # XXX: isn't this 0? elsif ($flag & O_WRONLY) { ($flag & O_APPEND) ? "a" : "w" } elsif ($flag & O_RDWR) { if ($flag & O_CREAT) { "w+" } else { ($flag & O_APPEND) ? "a+" : "r+" } } }; Or print do { ($flags & O_WRONLY) ? "write-only" : ($flags & O_RDWR) ? "read-write" : "read-only"; }; Or if you are certainly that all the && clauses are true, you can use something like this, which ``switches'' on the value of the HTTP_USER_AGENT envariable. #!/usr/bin/perl # pick out jargon file page based on browser $dir = 'http://www.wins.uva.nl/~mes/jargon'; for ($ENV{HTTP_USER_AGENT}) { $page = /Mac/ && 'm/Macintrash.html' || /Win(dows )?NT/ && 'e/evilandrude.html' || /Win|MSIE|WebTV/ && 'm/MicroslothWindows.html' || /Linux/ && 'l/Linux.html' || /HP-UX/ && 'h/HP-SUX.html' || /SunOS/ && 's/ScumOS.html' || 'a/AppendixB.html'; } print "Location: $dir/$page\015\012\015\012"; That kind of switch statement only works when you know the && clauses will be true. If you don't, the previous ?: example should be used. You might also consider writing a hash instead of synthesizing a switch statement.

2. edurles

   On 2006-08-15 02:50:44

   
   
   I am not going to write the program for you, but just to let you know that even the logic is incorrect. You have to use a while loop, not a do-while. Put the "Do you have anymore cars?" before the while loop, and then after the "what year was it made?", like print "Do you have anymore cars?\n"; chomp $morecars = ; $morecars = lc $morecars; # This is to convert to lower case, so # it's easier while ($morecars ne "no") { ... ... print "what year was it made? \n"; chomp $year = ; print "Do you have anymore cars?\n"; chomp $morecars = ; $morecars = lc $morecars; } The second issue is that you are not using arrays!! You should have somehitng like this: my @years; my @name; and then in the loop $year[$n] = ; etc.. Anyway, it doesnt seem to me you have a lot of programming experience, so I recommend you read a bit more about Perl and then try again. Things will become clearer and you'll come up with a much better solution, as this one is so cumbersome and cheesy....

3. timespiral

   On 2006-08-15 15:32:50

   
   
   I added comments (#) to help you. This is the basic idea on how to do it. When in doubt, print it out. For debugging, using the print command and exit command is useful. Anytime you can isolate a problem it makes your debugging easier. If something isn't working right just comment it out as this will help to identify the errors. my $morecars = "yes"; #initialize #for(initialize counter; loop termination condition; increment counter) for (my $i = 0; $morecars ne "no"; $i++) { print "What make is the car? \n"; $name[$i] = ; chomp $name[$i]; #remove whitespace print "what year was it made? \n"; $year[$i] = ; chomp $year[$i]; print &CarAge($year[$i]); #call subroutine to test #the year.. assume 4 digit #year. In real world you #would have to make sure #it is in the right format #and not rely on users. print "\n\nDo you have anymore cars? \n"; $morecars = ; chomp $morecars; $morecars = lc($morecars); # convert to lower case #to comply with termination #test in for loop. } # sub CarAge # accepts the year # the car was created # which is called "born" # in this example sub CarAge { my $born = shift; #store the paramater #passed to this subroutine #in variable $born. my $age = 2006 - $born; #compute age my $text = "Your car is a baby."; if ($age > 6) { $text = "Your car is older than the hills."; } return $text; }