有人可以解释为什么以下代码……
#!/opt/local/bin/perl use strict; use warnings; my $string; $string = "\t\t\tEntry"; print "String: >$string<\n"; $string =~ s/^(\t*)//gi; print "\$1: >$1<\n"; print "String: >$string<\n"; print "\n"; $string = "\t\t\tEntry"; $string =~ s/^(\t*)([^\t]+)/$2/gi; print "\$1: >$1<\n"; print "String: >$string<\n"; print "\n"; exit 0;
…产生以下输出……
String: > Entry< Use of uninitialized value in concatenation (.) or string at ~/sandBox.pl line 12. $1: >< String: >Entry< $1: > < String: >Entry<
……或更直接：为什么第一次替换中的匹配值不会保留在$1中？
解决方法
我在Perl 5.12的两个实现上尝试了这个,并没有遇到问题. 5.8做了.
因为你有g选项,perl会尝试匹配模式,直到它失败.请参阅下面的调试输出.
所以它在Perl 5.8中不起作用,但这样做：
my $c1; $string =~ s/^(\t*)/$c1=$1;''/ge;
因此,每次匹配时,它将其保存到$c1.
这就是重新’调试’告诉我的用法：
Compiling REx `^(\t*)'
size 9 Got 76 bytes for offset annotations.
first at 2
1: BOL(2)
2: OPEN1(4)
4: STAR(7)
5: EXACT <\t>(0)
7: CLOSE1(9)
9: END(0)
anchored(BOL) minlen 0
Offsets: [9]
1[1] 2[1] 0[0] 5[1] 3[1] 0[0] 6[1] 0[0] 7[0]
Compiling REx `^(\t*)([^\t]+)'
size 25 Got 204 bytes for offset annotations.
first at 2
1: BOL(2)
2: OPEN1(4)
4: STAR(7)
5: EXACTF <\t>(0)
7: CLOSE1(9)
9: OPEN2(11)
11: PLUS(23)
12: ANYOF[\0-\10\12-\377{unicode_all}](0)
23: CLOSE2(25)
25: END(0)
anchored(BOL) minlen 1
Offsets: [25]
1[1] 2[1] 0[0] 5[1] 3[1] 0[0] 6[1] 0[0] 7[1] 0[0] 13[1] 8[5] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 14[1] 0[0] 15[0]
String: > Entry<
Matching REx `^(\t*)' against ` Entry'
Setting an EVAL scope,savestack=5
0 <> < Entry> | 1: BOL
0 <> < Entry> | 2: OPEN1
0 <> < Entry> | 4: STAR
EXACT <\t> can match 3 times out of 2147483647...
Setting an EVAL scope,savestack=5
3 < > <Entry> | 7: CLOSE1
3 < > <Entry> | 9: END
Match successful!
match pos=0
Use of uninitialized value in substitution iterator at - line 11.
Matching REx `^(\t*)' against `Entry'
Setting an EVAL scope,savestack=5
3 < > <Entry> | 1: BOL
Failed...
Match Failed
Freeing REx: `"^(\\t*)"'
Freeing REx: `"^(\\t*)([^\\t]+)"'
因为你试图在行的开头匹配空格,所以既不需要g也不需要i.所以你可能会尝试做别的事情.