perl中$/的作用

$/在perl中是輸入記錄分隔符，影響perl對"行"的理解。默認是換行符"\n".也可以定義爲其他的內容：

需要特別注意的是，$/的值是字符串，不是模式匹配。

1> 不修改$/的內容，默認爲"\n"

eg: test.pl

open WRI, "<test.pl";
$content = <WRI>; #讀取一行
@lines = <WRI>;  #將讀取的所有行放入@lines數組中。
close WRI;
#foreach my $line (@lines){
#    print "$line";
#}

print "$content";

輸出：

test]# perl test.pl
open WRI, "<test.pl";
test]#

2> 修改$/的值爲某一字符串：

open WRI, "<test.pl";
print "$/";
local $/ = "7799";        #或者是local $/=7799
#$content = <WRI>;
@lines = <WRI>;
close WRI;
$l = 1 ;
foreach my $line (@lines){
    print "line $l: $line\n";
    $l++;
}

輸出：

 test]# perl test.pl

line 1: open WRI, "<test.pl";
print "$/";
local $/ = "7799
line 2: ";
#$content = <WRI>;
@lines = <WRI>;
close WRI;
$l = 1 ;
foreach my $line (@lines){
    print "line $l: $line\n";
    $l++;
}

#print "$content";

 test]#

3> $\改成undef

open WRI, "<test.pl";
local $/ = undef;
#$content = <WRI>;
@lines = <WRI>;
close WRI;
$l = 1 ;
foreach my $line (@lines){
    print "line $l: $line\n";
    $l++;
}

#print "$content";

輸出：

test]# perl test.pl
line 1: open WRI, "<test.pl";
local $/ = undef;
#$content = <WRI>;
@lines = <WRI>;
close WRI;
$l = 1 ;
foreach my $line (@lines){
    print "line $l: $line\n";
    $l++;
}

#print "$content";


eg2：

open WRI, "<test.pl";
local $/ = undef;
$content = <WRI>;
#@lines = <WRI>;
close WRI;
#$l = 1 ;
#foreach my $line (@lines){
#    print "line $l: $line\n";
#    $l++;
#}

print "$content";

輸出：

test]# perl test.pl
open WRI, "<test.pl";
local $/ = undef;
$content = <WRI>;
#@lines = <WRI>;
close WRI;
#$l = 1 ;
#foreach my $line (@lines){
#    print "line $l: $line\n";
#    $l++;
#}

print "$content";

4>如果$/設爲整數、存有整數的標量或可轉換成整數的標量這些值的引用時，Perl會嘗試讀入記錄而不是行，最大記錄長度就是引用的那個整數。

eg:

open WRI, "<test.pl";
local $/ = \7;    #以7個記錄爲一行分開。
#$content = <WRI>;
@lines = <WRI>;
close WRI;
$l = 1 ;
foreach my $line (@lines){
    print "line $l: $line\n";
    $l++;
}

輸出：

test]# perl test.pl
line 1: open WR
line 2: I, "<te
line 3: st.pl";
line 4:
local
line 5: $/ = \7
line 6: ;
#$con
line 7: tent =
line 8: <WRI>;

line 9: @lines
line 10: = <WRI>
line 11: ;
close
line 12:  WRI;
$
line 13: l = 1 ;
line 14:
foreac
line 15: h my $l
line 16: ine (@l
line 17: ines){

line 18:     pri
line 19: nt "lin
line 20: e $l: $
line 21: line\n"
line 22: ;
    $
line 23: l++;
}

line 24:
#print
line 25:  "$cont
line 26: ent";