This variable stores the index of the first element in an array, and of the first character in a substring. The default is 0, but you could theoretically set it to 1 to make Perl behave more likeawk (or Fortran) when subscripting and when evaluating the index() and substr() functions.
As of release 5 of Perl, assignment to$[ is treated as a compiler directive, and cannot influence the behavior of any other file. (That's why you can only assign compile-time constants to it.) Its use is highly discouraged.
Prior to Perl v5.10.0, assignment to$[ could be seen from outer lexical scopes in the same file, unlike other compile-time directives (such asstrict). Using local() on it would bind its value strictly to a lexical block. Now it is always lexically scoped.
As of Perl v5.16.0, it is implemented by thearybase module.
As of Perl v5.30.0, or underuse v5.16, orno feature "array_base",$[ no longer has any effect, and always contains 0. Assigning 0 to it is permitted, but any other value will produce an error.
Mnemonic: [ begins subscripts.
Deprecated in Perl v5.12.0.
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