defined

NAME

defined - test whether a value, variable, or function is defined

SYNOPSIS

defined EXPR

DESCRIPTION

Returns a boolean value saying whether EXPR has a real value or not. Many operations return the undefined value under exceptional conditions, such as end of file, uninitialized variable, system error and such. This function allows you to distinguish between an undefined null scalar and a defined null scalar with operations that might return a real null string, such as referencing elements of an array. You may also check to see if arrays or subroutines exist. Use of defined on predefined variables is not guaranteed to produce intuitive results.

When used on a hash array element, it tells you whether the value is defined, not whether the key exists in the hash. Use exists() for that.

Examples:

print if defined $switch{'D'}; print "$val\n" while defined($val = pop(@ary)); die "Can't readlink $sym: $!" unless defined($value = readlink $sym); eval '@foo = ()' if defined(@foo); die "No XYZ package defined" unless defined %_XYZ; sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }