With DECC$EFS_CHARSET enabled, UNIX names can contain ODS-5
    extended characters. Support includes multiple dots and all ASCII
    characters in the range 0 to 255, except the following:

    <NUL>
    /         *
    "         ?

    Unless DECC$FILENAME_UNIX_ONLY is enabled, some characters can be
    interpreted as OpenVMS characters depending on context. They are:

    :         ^
    [         ;
    <

    DECC$EFS_CHARSET might be necessary for existing applications
    that make assumptions about filenames based on the presence
    of certain characters, because the following nonstandard and
    undocumented C RTL extensions do not work when EFS extended
    character-set support is enabled:

    o  $HOME is interpreted as the user's login directory

       With DECC$EFS_CHARSET enabled, $HOME is treated literally and
       may be in an OpenVMS or UNIX style filename.

    o  ~name is interpreted as the login directory for user name

       With DECC$EFS_CHARSET enabled, ~name is treated literally and
       can be in an OpenVMS or UNIX style filename.

    o  Wild card regular expressions in the form [a-z]

       With DECC$EFS_CHARSET enabled, square brackets are acceptable
       in OpenVMS and UNIX style filenames. For instance, in a
       function such as open, abc[a-z]ef.txt is interpreted as a
       UNIX style name equivalent to the OpenVMS style name abc^[a-
       z^]ef.txt, and [a-z]bc is interpreted as an OpenVMS style name
       equivalent to the UNIX style name /sys$disk/a-z/bc.

    With DECC$EFS_CHARSET enabled, the following encoding for EFS
    extended characters is supported when converting from an OpenVMS
    style filename to a UNIX style filename:

    o  All ODS-2 compatible names

    o  All encoding for 8-bit characters, either as single byte or
       using two-digit hexadecimal form ^ab. In a UNIX path these are
       always represented as a single byte.

    o  Encoding for DEL (^7F)

    o  The following characters when preceded by a caret:

       space ! , _ & ' ( ) + @ { } ; # [ ] % ^ = $ - ~ .

    o  The following characters when not preceded by a caret:

       $  -  ~  .

    o  The implementation supports the conversion from OpenVMS to
       UNIX needed for functions readdir, ftw, getname, fgetname,
       getcwd, and others.

                                   NOTE

       There are some special cases in C RTL filename processing.
       For example:

       o  Pathnames ending in ^.dir are treated as directories, and
          when translated, these characters are truncated from the
          string.

       o  Pathnames begining with ^/ treat the next token as a
          logical name or a directory from the root.

       The following sample program shows these nuances:

       #include <stdio.h>
       #include <dirent.h>
       #include <unixlib.h>
       #include <string.h>
       main()
       {
         char adir[80];
         DIR *dir;
         struct dirent *dp;
         int decc_feature_efs_charset_index = 0;
         int decc_feature_efs_charset_default_val = 0;

         if (
             ( (decc_feature_efs_charset_index =
               decc$feature_get_index("DECC$EFS_CHARSET")) == -1 )
             ||
             ( (decc_feature_efs_charset_default_val =
   decc$feature_get_value(decc_feature_efs_charset_index, 0)) == -1 )
             ||
 ( (decc$feature_set_value(decc_feature_efs_charset_index, 1, TRUE) == -1))
            )
           {
             printf("Error setting up DECC$EFS_CHARSET macro\n");
           }

         strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^,test^.dir^;22]");
         printf("\n\nFor %s\n", adir);
       mrb:  dir = opendir(adir);
         if(dir)
           {
             do
               {
                 dp = readdir(dir);
                 if(dp->d_name) printf("%s\n", dp->d_name);
               } while (dp);
           }

         closedir(dir);

         strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^,test^.dir]");
         printf("\n\nFor %s\n", adir);
         dir = opendir(adir);
         if(dir)
           {
             do
               {
                 dp = readdir(dir);
                 if(dp->d_name) printf("%s\n", dp->d_name);
               } while (dp);
           }

         closedir(dir);

         strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^\\test]");
         printf("\n\nFor %s\n", adir);
         dir = opendir(adir);
         if(dir)
           {
             do
               {
                 dp = readdir(dir);
                 if(dp->d_name) printf("%s\n", dp->d_name);
               } while (dp);
           }

         strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.copies]");
         printf("\n\nFor %s\n", adir);
         dir = opendir(adir);
         if(dir)
           {
             do
               {
                 dp = readdir(dir);
                 if(dp->d_name) printf("%s\n", dp->d_name);
               } while (dp);
           }

         closedir(dir);

         strcpy(adir, "/SYS$SYSDEVICE/SSHTEST/TEST/copies");
         printf("\n\nFor %s\n", adir);
         dir = opendir(adir);
         if(dir)
           {
             do
               {
                 dp = readdir(dir);
                 if(dp->d_name) printf("%s\n", dp->d_name);
               } while (dp);
           }

         closedir(dir);

       }