perl: 9月 2011

#Perl Hash Howto
http://www.cs.mcgill.ca/~abatko/computers/programming/perl/howto/hash/#initialize_a_hash_reference

#Camel perl 駱馬書hash 教學
http://easun.org/perl/perl-toc/ch05.html

迭代器敘述
last
next
continue
redo

Next
Continue
Last
Redo

goto Jumps to a specified label.

goto Syntax

goto LABEL #
goto EXPR #goto "ne"."xt"; <=> goto next; #維護性不高
goto &NAME #Can't goto subroutine outside a subroutine

next Syntax

next
next LABEL #

flowcontrol.pl:

#!/usr/bin/perl

print "content-type: text/html \n\n";

# SET A VARIABLE
$count = 0;
while ($count <= 7) {
  
 # SET A CONDITIONAL STATEMENT TO INTERRUPT @ 4
 if ($count == 4) {
  print "Skip Four!<br />";
  next;
 }
 # PRINT THE COUNTER
 print $count."<br />";

}
 continue {
  $count++;
 };
print "Loop Finished!";

flowcontrol.pl:

0
1
2
3
Skip Four!
5
6
7
Finished Counting!

Above, we skip the fourth iteration by incrementing the variable again. In the example we also print a line, "Skip Four!" just to make things easier to follow

指標參照：
$scalar = "1...10";
@array = (1...10);
%hash = (1...10);
$scalar_ref = \$scalar;
$array_ref = \@array;
$hash_ref = \%hash;

指標取元素值,雜湊,陣列：

my @array = qw/John Paul May/;    # 一個陣列
my $array_ref = \@array;    # 取得這個陣列的參照
print @{$array_ref};     # 印出JohnPaulMary
print ${$array_ref}[1];      # 印出John
my @aray = qw/John Paul May/;
my $array_ref = \@array;
for (@{$array_ref}) {
    print "姓名：$_\n";
}


my %hash = qw/John 24 Paul 30 May 26/;
my $hash_ref = \%hash;
print ${$hash_ref}{John};    # 果然印出 24
for (keys %{$hash_ref}) {
    print ${$hash_ref}{$_}."\n";   # 印出 24, 26, 30
}

%myhash = (
  "k1" => 10,
  "k2" => 8,
  "k3" => -9,
);

#排序技巧(sort by keys ,sort by values,other sorting technical)

@sortKey = sort {$a <=> $b} keys %myhash;
print "@sortKey\n";

@sortHashValue = sort {$a <=>$b} values %myhash;
print "@sortHashValue\n";

@sortKeyTech = sort {$myhash{$a} <=> $myhash{$b}} keys %myhash;
print "@sortKeyTech\n";

#關於for 迴圈的技巧

print "---technical 1:C-like for loop---\n";
for ($count=0;$count<=10;$count++){
print "the counter number is $count.\n";
}

print "---technical 2:range operator---\n";
for $count(1 .. 10){
print "the counter number is $count.\n";
}

print "---technical 3:simplified range operator---\n";
for (1 .. 10){
print "the counter number is $_."."\n";
}
print "---technical 4:push element into array with for loop---\n";
@arr=("initialization");
push (@arr, $_) for (1...10);
print "@arr";#initialization 1 2 3 4 5 6 7 8 9 10

#foreach 迴圈使用方法

@array=(1,2,3);

foreach my $element (@array)

print foreach (@array);   #印出123

不過這時候我們就用到了Perl最常用到的預設變數$_，當我們在迴圈中沒有指定任何變數時，Perl就會把取出來的值放入預設變數$_中。緊接著我們希望把迴圈取得的值列印出來，也就是執行
print $_;
這樣的式子，當然，這樣的式子在Perl出現的機率真是太少，因為大部份的時候，如果你只要列印單一的$_，Perl程式員也就會省略$_這個變數。而因為我們在迴圈中只打算執行print這個指令，所以倒裝句也就順勢產生。
#hash 的定義

%hash = (
"k1" => "v1",
"k2" => "v2",
"k3" => "v3",
"k4" => "v4",
);
#取出hash的keys存為陣列@keys
#取出hash的values存為陣列@values
#將陣列@keys中的元素取出使用
#利用while迴圈 each函數取出%hash的pair
@keys = keys(%hash);
@values = values(%hash);
for (@keys){print "$_ => $hash{$_}\n";}

while (($key, $value) = each (%hash)) {
# 取出雜湊中的每一對鍵值，並且分別放入$key, $value
print "$key => $value\n";
}

#因為Perl會把副常式中最後一個運算的值當成預設的回傳值，所以你可以省略在進行運算後還必須再進行一次return的動作

my $return = &square(4);
print $return;

sub square {
    my $base = shift;
    $base**2;
}

my $return = &div(4, 2);   # 這時候有兩個參數
print $return;

sub div {
    $_[0]/$_[1];    # 只是進行除法
}

不過如果我們在叫用副常式的時候傳了三個參數，就像：

&div(4, 2, 6);

那會產生什麼結果呢？其實回傳值就跟原來的一樣，因為Perl並不會去在意參數的個數問題。f若程式有需要，應該去確認參數的個數，避免參數個數無法應付需要，以確保程式能正常而順利的進行。

#取得陣列或@_中的最大執與最小值

sub getmin{
@sorted = sort @_;
print "@sorted";
$min = shift @_;
print "\nmin : $min\n";
return $min;
}
getmin(1,2,3,4);

sub getmax{
@sorted = sort @_;
print "@sorted";
$max = shift @_;
print "\nmax : $max\n";
return $max;
}
getmax(1,2,3,4);

#陣列的資料取出陣列取出元素數量
@array = (1..10);
my @array2 = @array; #指定陣列給@array2
my $eleNum = @array; #取出陣列的元素數量

print "@array\n";
print "@array2\n";
print $eleNum;

my @array = (1...10); # 利用串列賦值給陣列
my $scalar = @array + 4; # 在純量語境中進行 $scalar=14
my @scalar_array = @array + 4;# 先以純量語境進行運算，然後以串列方式賦值給陣列

print "@array\n";
print "$scalar\n"; # 在純量語境中進行 $scalar=14
print "@scalar_array"; #@scalar_arrray=(14)

@arr=(1..10);
print $#arr; # 印出陣列arr的最大index值,其中$#arr 為9

##找出陣列元素是否存在的辦法
##exists argument MUST BE a HASH or ARRAY element or a subroutine !!
@arr -= (1..10);
print "IT EXIST!!!\n" if (exist $arr[11]); #查看arr[11]是否存在

#找出hash值是否存在的辦法

my %hash = (
            'cd' => 2,
            'book' => 10,
            'video' => 0,
            );
my $media = 'video';
print "bingo" if ($hash{$media});

$_:預設參數
@_:預設參數陣列
$#_:預設參數的最大index值

#subroutine 的參數數量

sub stayFunc{
$numPara = $#_+1;
print "你輸入了$numPara個參數";
print "這些參數分別為:\n";
for (@_){
print "[para]:".$_."\n";
}
print "\tstayFunc執行結束...\n";
}
stayFunc(1,2,"three");
##執行結果
##你輸入了3個參數這些參數分別為:
##[para]:1
##[para]:2
##[para]:three
## stayFunc執行結束...

#比較my和local之間的差別

$var1 = "global";
$var2 = "for local";
&sub1;      # 印出 local, for local
&sub2;      # 印出 global, for local

sub sub1 {
    local $var1 = "local";
    my $var2 = "my";
    &sub2;
}

sub sub2 {
    print "var1=$var1\tvar2=$var2\n";
}

#計數器在等於8時執行redo敘述
#導致從block的開頭再執行一次程式碼此時計數器仍為8
#故印出無窮個8
for (1..10){
if ($_ == 8){
print $_;
redo;
}
}
#印出無限個88888888....

Syntax

redo LABEL

redo

myLabel{
print "Hello";
redo myLabel;
}

#三元運算符

my ($a, $b) = (42, 22);
my $max = ($a > $b) ? $a : $b;
print "$max\n";

Syntax(Raise an Exception)

die LIST

Definition and Usage

Prints the value of LIST to STDERR and calls exit with the error value contained in $!.

Return Value

Nothing

Example

Following are the usage...

die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
or
    chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"
or
    open( FILEH, ">/tmp/test" ) || die( "Can't open file test $!\n" );

output() || die "沒有回傳值";

sub output {
    return 0;
}

#do 敘述的使用

do BLOCK
do SUBROUTINE(LIST)
do EXPR

open FILE,"myfile.txt" or die "Exception:$!";
print FILE "my message";

#取出陣列@arr裡面前兩個元素指定給變數
@arr = (1..10);
($first,$secondary)=@arr;
print "$first\t$secondary"; # $first 為1#$secondary為2

#將字串轉成字元陣列後再進行操作

@strArr = split ("",$input ); #字串轉成字元陣列
print "\@strArr = >@strArr";
print "$_\n" for(@strArr);
print $strArr[0];

perl

2011年9月30日星期五

perl note

goto Syntax

goto LABEL #
goto EXPR #goto "ne"."xt"; <=> goto next; #維護性不高
goto &NAME #Can't goto subroutine outside a subroutine

next Syntax

next
next LABEL #

next Syntax

next
next LABEL #

flowcontrol.pl:

flowcontrol.pl:

Syntax

Syntax(Raise an Exception)

Definition and Usage

Return Value

Example

2011年9月22日星期四

perl study resource

2011年9月30日 星期五

perl note

goto Syntax goto LABEL #goto EXPR #goto "ne"."xt"; <=> goto next; #維護性不高goto &NAME #Can't goto subroutine outside a subroutine

next Syntax next next LABEL #

next Syntax next next LABEL #

flowcontrol.pl:

flowcontrol.pl:

Syntax

Syntax(Raise an Exception)

Definition and Usage

Return Value

Example

2011年9月22日 星期四

perl study resource

2011年9月30日星期五

goto Syntax

goto LABEL #
goto EXPR #goto "ne"."xt"; <=> goto next; #維護性不高
goto &NAME #Can't goto subroutine outside a subroutine

next Syntax

next
next LABEL #

next Syntax

next
next LABEL #

2011年9月22日星期四