Perl通常会抱怨实际错误,例如当变量只使用一次时：
use warnings;
if ( 0 ) {
} elsif ( $test ) { } # line 3
# Name "main::test" used only once: possible typo at testt.pl line 3.
这对于使用未初始化的$_的警告不起作用：
use warnings;
if ( 0 ) { # line 2
} elsif ( chomp ) { }
# Use of uninitialized value $_ in scalar chomp at testt.pl line 2.
use warnings;
if ( 0 ) { # line 2
} elsif ( m/test/ ) { }
# Use of uninitialized value $_ in pattern match (m//) at testt.pl line 2.
是什么导致这个？这种行为何时有用？
解决方法
perldoc perl5101delta：
The line numbers for warnings inside
elsif are now correct.
请注意,此更改仅影响elsif;您仍会看到运行时错误/警告给出语句的开头或结尾行号而不是违规代码的实际行：
$perl
use warnings;
0 ? do {
} : $test ? do {
} : do { };
0 ? do {
} : chomp() ? do {
} : do { };
Name "main::test" used only once: possible typo at - line 3. # correct
Use of uninitialized value $_ in scalar chomp at - line 8. # incorrect