Perldoc Search: "$(" perl-5.20.1

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4 PODs, 10 LINEs found.
120 :     $(      The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by "getgid()", and the subsequent ones by "getgroups()", one of which may be the same as the first number.
122 :             However, a value assigned to $( must be a single number used to set the real gid. So the value given by $( should *not* be assigned back to $( without being forced numeric, such as by adding zero. Note that this is different to the effective gid ($)) which does take a list.
124 :             You can change both the real gid and the effective gid at the same time by using "POSIX::setgid()". Changes to $( require a check to $! to detect any possible errors after an attempted change.
136 :             $<, $>, $( and $) can be set only on machines that support the corresponding *set[re][ug]id()* routine. $( and $) can be swapped only on machines supporting "setregid()".
1025 :             PATTERN may contain variables, which will be interpolated every time the pattern search is evaluated, except for when the delimiter is a single quote. (Note that $(, $), and $| are not interpolated because they look like end-of-string tests.) Perl will not recompile the pattern unless an interpolated variable that it contains changes. You can force Perl to skip the test and never recompile by adding a "/o" (which stands for "once") after the trailing delimiter. Once upon a time, Perl would recompile regular expressions unnecessarily, and this modifier was useful to tell it not to do so, in the interests of speed. But now, the only reasons to use "/o" are one of:
1247 :                 s/\$(\w+)/${$1}/g;
1632 :             Interpolation in patterns has several quirks: $|, $(, $), "@+" and "@-" are not interpolated, and constructs $var[SOMETHING] are voted (by several different estimators) to be either an array element or $var followed by an RE alternative. This is where the notation "${arr[$bar]}" comes handy: "/${arr[0-9]}/" is interpreted as array element -9, not as a regular expression from the variable $arr followed by a digit, which would be the interpretation of "/$arr[0-9]/". Since voting among different estimators may occur, the result is not predictable.
2290 :         If instead you intended to match the word 'foo' at the end of the line followed by whitespace and the word 'bar' on the next line then you can use "m/$(?)\/" (for example: "m/foo$(?)\s+bar/").
2573 :         (F) You tried to assign to $(, and your operating system doesn't support the setrgid() system call (or equivalent), or at least Configure didn't think so.
345 :     Don't assume the Unix user and group semantics: especially, don't expect the $< and $> (or the $( and $)) to work for switching identities (or memberships).
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