do - turn a BLOCK into a TERM

- NAME
- SYNOPSIS
- DESCRIPTION

# NAME

do - turn a BLOCK into a TERM

# SYNOPSIS

do BLOCK

do `SUBROUTINE(LIST)`

do EXPR

# DESCRIPTION

Not really a function. Returns the value of the last command in the sequence of commands indicated by BLOCK. When modified by the `while` or `until` loop modifier, executes the BLOCK once before testing the loop condition. (On other statements the loop modifiers test the conditional first.)

`do BLOCK` does not count as a loop, so the loop control statements `next`, `last`, or `redo` cannot be used to leave or restart the block. See the perlsyn manpage for alternative strategies.

This form of subroutine call is deprecated. See the perlsub manpage.

Uses the value of EXPR as a filename and executes the contents of the file as a Perl script.

        do 'stat.pl';

is just like

        eval `cat stat.pl`;

except that it's more efficient and concise, keeps track of the current filename for error messages, searches the @INC directories, and updates `%INC` if the file is found. See Predefined Names in the perlvar manpage 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;
            }
        }

do - turn a BLOCK into a TERM