我有一个SQL Select转储，其中许多行看起来像这样：
07/11/2011 16:48:08,07/11/2011 16:48:08,'YD','MANUAL',0,1,'text','text','text','text',,,,'text',,,0,0,
我想对每一行做两件事：
sysdate函数替换所有日期。日期也可以没有时间（如07/11/2011）。null字符串这是我的尝试：
$_ =~ s/,(,|\n)/,null$1/g; # Replace no data by "null"
$_ =~ s/\d{2}\/\d{2}\/d{4}.*?,/sysdate,/g; # Replace dates by "sysdate"
但是这会将字符串转换为：
07/11/2011 16:48:08,07/11/2011 16:48:08,'YD','MANUAL',0,1,'text','text','text','text',null,,null,'text',null,,0,0,null
虽然我希望它是
sysdate,sysdate,'YD','MANUAL',0,1,'text','text','text','text',null,null,null,'text',null,null,0,0,null
我不明白为什么日期不匹配以及为什么某些,,不会被null取代。
任何见解都欢迎，提前谢谢。
答案 0 :(得分：1)
你可以这样做：
$ cat perlregex.pl
use warnings;
use strict;
my $row = "07/11/2011 16:48:08,07/11/2011 16:48:08,'YD','MANUAL',0,1,'text','text','text','text',,,,'text',,,0,0,\n";
print( "$row\n" );
while ( $row =~ /,([,\n])/ ) { $row =~ s/,([,\n])/,null$1/; }
print( "$row\n" );
$row =~ s/\d{2}\/\d{2}\/\d{4}.*?,/sysdate,/g;
print( "$row\n" );
结果如下：
$ ./perlregex.pl
07/11/2011 16:48:08,07/11/2011 16:48:08,'YD','MANUAL',0,1,'text','text','text','text',,,,'text',,,0,0,
07/11/2011 16:48:08,07/11/2011 16:48:08,'YD','MANUAL',0,1,'text','text','text','text',null,null,null,'text',null,null,0,0,null
sysdate,sysdate,'YD','MANUAL',0,1,'text','text','text','text',null,null,null,'text',null,null,0,0,null
这当然可以进行优化，但它可以解决问题。
答案 1 :(得分：1)
\d{2}\/\d{2}\/d{4}.*?,无效，因为最后d未被转义
如果,可以位于字符串的任一侧或开头/结尾，则可以分两步执行：
第1步
s/(?:^|(?<=,))(?=,|\n)/null/g
的展开：
/
(?: ^ # Begining of line, ie: nothing behind us
| (?<=,) # Or, a comma behind us
)
# we are HERE!, this is the place between characters
(?= , # A comma in front of us
| \n # Or, a newline in front of us
)
/null/g
# The above regex does not consume, it just inserts 'null', leaving the
# same search position (after the insertion, but before the comma).
# If you want to consume a comma, it would be done this way:
s/(?:^|(?<=,))(,|\n)/null$1/xg
# Now the search position is after the 'null,'
第2步
s/(?:^|(?<=,))\d{2}\/\d{2}\/\d{4}.*?(?=,|\n)/sysdate/g
或者，您可以使用eval修饰符将它们组合成单个正则表达式：
$row =~ s/(?:^|(?<=,))(\d{2}\/\d{2}\/\d{4}.*?|)(?=,|\n)/ length $1 ? 'sysdate' : 'null'/eg;
分解它看起来像这样
s{
(?: ^ | (?<=,) ) # begin of line or comma behind us
( # Capt group $1
\d{2}/\d{2}/\d{4}.*? # date format and optional non-newline chars
| # Or, nothing at all
) # End Capt group 1
(?= , | \n ) # comma or newline in front of us
}{
length $1 ? 'sysdate' : 'null'
}eg
如果有可能出现非换行空白填充，则可以写成：
$row =~ s/(?:^|(?<=,))(?:([^\S\n]*\d{2}\/\d{2}\/\d{4}.*?)|[^\S\n]*)(?=,|\n)/ defined $1 ? 'sysdate' : 'null'/eg;
答案 2 :(得分：1)
你想要替换一些东西。通常前瞻是一个更好的选择：
$subject =~ s/(?<=,)(?=,|$)/null/g;
说明：
"
(?<= # Assert that the regex below can be matched, with the match ending at this position (positive lookbehind)
, # Match the character “,” literally
)
(?= # Assert that the regex below can be matched, starting at this position (positive lookahead)
# Match either the regular expression below (attempting the next alternative only if this one fails)
, # Match the character “,” literally
| # Or match regular expression number 2 below (the entire group fails if this one fails to match)
\$ # Assert position at the end of the string (or before the line break at the end of the string, if any)
)
"
您希望更换日期：
$subject =~ s!\d{2}/\d{2}/\d{4}.*?(?=,)!sysdate!g;
这与原始正则表达式几乎相同。用前瞻替换最后一个。 （如果您不想替换它，请不要匹配它。）
# \d{2}/\d{2}/\d{4}.*?(?=,)
#
# Match a single digit 0..9 «\d{2}»
# Exactly 2 times «{2}»
# Match the character “/” literally «/»
# Match a single digit 0..9 «\d{2}»
# Exactly 2 times «{2}»
# Match the character “/” literally «/»
# Match a single digit 0..9 «\d{4}»
# Exactly 4 times «{4}»
# Match any single character that is not a line break character «.*?»
# Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
# Assert that the regex below can be matched, starting at this position (positive lookahead) «(?=,)»
# Match the character “,” literally «,»
答案 3 :(得分：0)
也许。*？太贪心了，试试：
$_ =~ s/\d{2}\/\d{2}\/d{4}[^,]+,/sysdate,/g;