검색어: unsetting (한국어 - 영어)

that means, for example, that unsetting $var won't unset global variable.
$var = $globals[ "var"];

the settings of pcre_caseless, pcre_multiline, pcre_dotall, and pcre_extended can be changed from within the pattern by a sequence of perl option letters enclosed between "(?" and ")". the option letters are i for pcre_caseless m for pcre_multiline s for pcre_dotall x for pcre_extended for example, (?im) sets caseless, multiline matching. it is also possible to unset these options by preceding the letter with a hyphen, and a combined setting and unsetting such as (?im-sx), which sets pcre_caseless and pcre_multiline while unsetting pcre_dotall and pcre_extended, is also permitted. if a letter appears both before and after the hyphen, the option is unset. the scope of these option changes depends on where in the pattern the setting occurs. for settings that are outside any subpattern (defined below), the effect is the same as if the options were set or unset at the start of matching. the following patterns all behave in exactly the same way: (?i)abc a(?i)bc ab(?i)c abc(?i) which in turn is the same as compiling the pattern abc with pcre_caseless set. in other words, such "top level" settings apply to the whole pattern (unless there are other changes inside subpatterns). if there is more than one setting of the same option at top level, the rightmost setting is used. if an option change occurs inside a subpattern, the effect is different. this is a change of behaviour in perl 5.005. an option change inside a subpattern affects only that part of the subpattern that follows it, so (a(?i)b)c matches abc and abc and no other strings (assuming pcre_caseless is not used). by this means, options can be made to have different settings in different parts of the pattern. any changes made in one alternative do carry on into subsequent branches within the same subpattern. for example, (a(?i)b_bar_c) matches "ab", "ab", "c", and "c", even though when matching "c" the first branch is abandoned before the option setting. this is because the effects of option settings happen at compile time. there would be some very weird behaviour otherwise. the pcre-specific options pcre_ungreedy and pcre_extra can be changed in the same way as the perl-compatible options by using the characters u and x respectively. the (?x) flag setting is special in that it must always occur earlier in the pattern than any of the additional features it turns on, even when it is at top level. it is best put at the start.
for example, when it is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()for example, when it is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() it yields "no match "quickly.