25.4. System Interaction
Platforms that rely on a graphical user interface sometimes
lack command lines, so programs requiring a command-line interface
might not work everywhere. You can't do much about this, except upgrade.
Some other tips:
Some platforms can't delete or rename files that are in use, so remember to close files when you are done
with them. Don't unlink or rename an open file. Don't tie
or open a file already tied or opened; untie or close it
Don't open the same file more than once at a time for writing, since some
operating systems put mandatory locks on such files.
Don't depend on a specific environment variable existing in
%ENV, and don't assume that anything in
%ENV will be case sensitive or case preserving.
Don't assume Unix inheritance semantics for environment
variables; on some systems, they may be visible to all other processes.
Don't use signals or %SIG.
Try to avoid filename globbing. Use opendir, readdir, and
closedir instead. (As of release 5.6.0 of Perl, basic filename
globbing is much more portable than it was, but some systems may still
chafe under the Unixisms of the default interface if you try to get
Don't assume specific values of the error numbers or strings stored in
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