On 22/08/19 2:20 AM, Warren Young wrote: > On Aug 21, 2019, at 7:35 AM, Xinhuan Zheng <xzheng at christianbook.com> wrote: >> >> my $s = IO::Select->new( $fh ); >> if ( $io->can_write( 10 ) { > > That’s not designed to do what you hope. select(2) is a system call intended for use on network socket handles, not file handles. Since socket handles and file handles are compatible on a Unix type system (including CentOS) the call doesn’t fail, but it *cannot* report the information you’re hoping to get. > > I would first try calling the -w operator: > > print_to_file() if -w $fh; First off I would be remiss if I didn't point out that CentOS 5 has been EOL for years, that said... You're dealing with perl here and so this might be better off asking in a perl list. The -X system of tests as documented with "perldoc -f -X" do not by default test actual ability to read and write files, but instead just check the file mode bits as returned by stat(), thus the -w test will not reflect the filesystem being in read-only mode. There are two ways to get around this. One is to to use the filetest pragma which changes the behavior of the -X tests to use the access(2) system function: { use filetest 'access'; print_to_file() if -w $fh; } The other way is to use POSIX::access() directly (this requires the file name or path): use POSIX qw(access W_OK); ... print_to_file() if access($filepath, W_OK); Note that there are caveats to either of the above approaches as per documentation. See the following for additional info: perldoc -f -X perldoc filetest access(2) Peter