Perl File Test Operators

Example	True if file named in $a
-r $a	is readable by effective uid/gid
-w $a	is writable effective uid/gid
-x $a	is executable effective uid/gid
-o $a	is owned effective uid/gid
-R $a	is readable by real uid/gid
-W $a	is writable real uid/gid
-X $a	is executable real uid/gid
-O $a	is owned real uid/gid
-e $a	exists
-z $a	has zero size
-s $a	has non-zero size
-b $a	is a block special
-c $a	is a character special
-d $a	is a directory
-f $a	is a plain file
-p $a	is a named pipe (fifo)
-S $a	is a socket
-l $a	is a symbolic link
-t $a	is a opened to a tty
-T $a	is a text file
-B $a	is a binary file
-u $a	has setuid bit set
-g $a	has setgid bit set
-k $a	has sticky bit set
-M $a	Age of file (at startup) in days since modification (floating)
-A $a	Age of file (at startup) in days since last access (floating)
-C $a	Age of file (at startup) in days since inode change(floating)

Age, stored in $^T, can be negative
if file changed after script started.
Examples:
-e "/usr/bin/perl" or warn "Perl is improperly installed\n";
-f "/vmunix" and print "Congrats, we seem to be running BSD Unix\n";

Note: The underscore in the following test:

print "Can do.\n if -r $a || -w _ || -x _;

Uses the stat structure of the previous file test (or stat operator), thereby saving a system call. (Does not work with -t, and remember that lstat and -l leave values in the stat structure for the symbolic link, not the real file).