Uses the value of EXPR as a filename and executes the contents of the file as a Perl
script. Its primary use is to include subroutines from a Perl subroutine library.
is just like
except that it's more efficient and concise, keeps track of the current filename for
error messages, searches the @INC libraries, and updates %INC if the file is
found. See perlvar/Predefined
Names for these variables. It also differs in that code evaluated with do
FILENAME cannot see lexicals in the enclosing scope; eval STRING does.
It's the same, however, in that it does reparse the file every time you call it, so you
probably don't want to do this inside a loop.
If do cannot read the file, it returns undef and sets $! to
the error. If do can read the file but cannot compile it, it returns undef
and sets an error message in $@. If the file is successfully compiled, do
returns the value of the last expression evaluated.
Note that inclusion of library modules is better done with the use and require
operators, which also do automatic error checking and raise an exception if there's a
problem.
You might like to use do to read in a program configuration file. Manual
error checking can be done this way:
# read in config files: system first, then user
for $file ("/share/prog/defaults.rc",
"$ENV{HOME}/.someprogrc")
{
unless ($return = do $file) {
warn "couldn't parse $file: $@" if $@;
warn "couldn't do $file: $!" unless defined $return;
warn "couldn't run $file" unless $return;
}
}
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