require VERSION require EXPR require Demands a version of Perl specified by VERSION, or demands some semantics specified by EXPR or by $_ if EXPR is not supplied. VERSION may be either a numeric argument such as 5.006, which will be compared to $] , or a literal of the form v5.6.1, which will be compared to $^V (aka $PERL_VERSION). An exception is raised if VERSION is greater than the version of the current Perl interpreter. Compare with use, which can do a similar check at compile time. Specif

Relational Operators Perl operators that return true or false generally return values that can be safely used as numbers. For example, the relational operators in this section and the equality operators in the next one return 1 for true and a special version of the defined empty string, "" , which counts as a zero but is exempt from warnings about improper numeric conversions, just as "0 but true" is. Binary "<" returns true if the left argument is numerically less than the right argument.

rename OLDNAME,NEWNAME Changes the name of a file; an existing file NEWNAME will be clobbered. Returns true for success, false otherwise. Behavior of this function varies wildly depending on your system implementation. For example, it will usually not work across file system boundaries, even though the system mv command sometimes compensates for this. Other restrictions include whether it works on directories, open files, or pre-existing files. Check perlport and either the rename(2) manpage or

reset EXPR reset Generally used in a continue block at the end of a loop to clear variables and reset ?? searches so that they work again. The expression is interpreted as a list of single characters (hyphens allowed for ranges). All variables and arrays beginning with one of those letters are reset to their pristine state. If the expression is omitted, one-match searches (?pattern? ) are reset to match again. Only resets variables or searches in the current package. Always returns 1. Examples:

Regexp Quote-Like Operators Here are the quote-like operators that apply to pattern matching and related activities. qr/STRING/msixpodualn This operator quotes (and possibly compiles) its STRING as a regular expression. STRING is interpolated the same way as PATTERN in m/PATTERN/. If "'" is used as the delimiter, no interpolation is done. Returns a Perl value which may be used instead of the corresponding /STRING/msixpodualn expression. The returned value is a normalized version of the origi

redo LABEL redo EXPR redo The redo command restarts the loop block without evaluating the conditional again. The continue block, if any, is not executed. If the LABEL is omitted, the command refers to the innermost enclosing loop. The redo EXPR form, available starting in Perl 5.18.0, allows a label name to be computed at run time, and is otherwise identical to redo LABEL . Programs that want to lie to themselves about what was just input normally use this command: # a simpleminded Pascal comme

ref EXPR ref Returns a non-empty string if EXPR is a reference, the empty string otherwise. If EXPR is not specified, $_ will be used. The value returned depends on the type of thing the reference is a reference to. Builtin types include: SCALAR ARRAY HASH CODE REF GLOB LVALUE FORMAT IO VSTRING Regexp You can think of ref as a typeof operator. if (ref($r) eq "HASH") { print "r is a reference to a hash.\n"; } unless (ref($r)) { print "r is not a reference at all.\n"; } The return value

readpipe EXPR readpipe EXPR is executed as a system command. The collected standard output of the command is returned. In scalar context, it comes back as a single (potentially multi-line) string. In list context, returns a list of lines (however you've defined lines with $/ or $INPUT_RECORD_SEPARATOR ). This is the internal function implementing the qx/EXPR/ operator, but you can use it directly. The qx/EXPR/ operator is discussed in more detail in I/O Operators in perlop. If EXPR is omitted,

readlink EXPR readlink Returns the value of a symbolic link, if symbolic links are implemented. If not, raises an exception. If there is a system error, returns the undefined value and sets $! (errno). If EXPR is omitted, uses $_ . Portability issues: readlink in perlport.

readline EXPR readline Reads from the filehandle whose typeglob is contained in EXPR (or from *ARGV if EXPR is not provided). In scalar context, each call reads and returns the next line until end-of-file is reached, whereupon the subsequent call returns undef. In list context, reads until end-of-file is reached and returns a list of lines. Note that the notion of "line" used here is whatever you may have defined with $/ or $INPUT_RECORD_SEPARATOR ). See $/ in perlvar. When $/ is set to undef,