Programming Perl, 4th Edition

tie

tie VARIABLE, CLASSNAME, LIST

This function binds a variable to a package class that will provide the implementation for the variable. VARIABLE is the variable (scalar, array, or hash) or typeglob (representing a filehandle) to be tied. CLASSNAME is the name of a class implementing objects of an appropriate type.

Any additional arguments are passed to the appropriate constructor method of the class, meaning one of TIESCALAR, TIEARRAY, TIEHASH, or TIEHANDLE. (If the appropriate method is not found, an exception is raised.) Typically, these are arguments such as might be passed to the dbm_open(3) function of C, but their meaning is package dependent. The object returned by the constructor is in turn returned by the tie function, which can be useful if you want to access other methods in CLASSNAME. (The object can also be accessed through the tied function.) So a class for tying a hash to an I SAM implementation might provide an extra method to traverse a set of keys sequentially (the “S” of I SAM), since your typical DBM implementation can’t do that.

Functions such as keys and values may return huge list values when used on large objects like DBM files. You may prefer to use the each function to iterate over such. For example:

use NDBM_File; tie(%ALIASES, "NDBM_File", "/etc/aliases", 1, 0) || die "Can't open aliases: $!"; while (($key,$val) = each %ALIASES) { say "$key = $val"; } untie ...