read20 - read a tape produced by the TOPS-20 Dumper Program

     read20 [-f tapefile] [-t]  [-x]  [-v]  [-c]  [-T]  [-g]  [-e
     expression] [-S ssnums...] [-F filenums...] [string...]

     Read20 reads  tapes  produced  by  the  TOPS-20  backup  and
     archival  program  DUMPER,  producing directory listings and
     extracting files.  The -t option specifies a directory list-
     ing,  and  the -x option specifies extraction.  Both actions
     can be specified.

     If no string, -e, -F, or -S option is given, every  file  on
     the  tape  is  processed.  Otherwise, every file with a name
     that either contains string ..., matches (as in  ed(1))  the
     regular  expression expression, or is selected by the -S and
     -F options will be processed.  The last two options are used
     to  select files by saveset number and file number.  This is
     useful when extracting from  an  archive  tape.   The  most-
     recently  specified  saveset  number  is associated with the
     specified file numbers.  The TOPS-20  filenames  are  lower-
     cased  before  any matching.  Note that string is not a gen-
     eralized pattern, but  is  just  a  simple  string  that  is
     matched  against  all the characters in the filenames.  Spe-
     cial characters (such as '<' and '>') must be quoted to  get
     past the shell.

     The UNIX filename of an extracted file is generated from the
     TOPS-20 filename by stripping off the device name, translat-
     ing the TOPS-20 directory syntax to a relative directory  in
     UNIX format, and stripping off the generation number, unless
     the -g flag is given.  Directories will be built  as  needed
     with  protection 775, but any existing directory or its con-
     tents will not be changed (unless an extracted file replaces
     one of the same name).

     The directory listing prints out for every file

          -- a ``flags'' field which indicates  if  the  file  is
          archived (A), offline (O), or invisible (I)
          -- the size in TOPS-20 pages  (for  offline  files  the
          size before archiving)
          -- the number of bytes in the file
          -- the bytesize (number of bits per byte) of the file
          -- the octal TOPS-20 file protection
          -- the time and date the file was last modified
          -- the full pathname of the file.

     If the -v flag is given, two additional fields  are  printed
     at the left:
     -- the saveset number
     -- the file number

     Read20 only extracts text files and 8-bit  files.   In  text
     files, unless the -c flag is given, carriage returns preced-
     ing linefeeds are removed.  The file length  as  printed  by
     the  `t' option is not adjusted to account for this.  Read20
     decides whether or not a  file  is  text  by  examining  the
     bytesize  of  the  file.  If the file has 7-bit bytes, it is
     assumed to be a text file.  If it has  8-bit  bytes,  it  is
     extracted  at  4  bytes/word,  including null bytes.  If the
     file has any other bytesize,  requests  to  extract  it  are

     Occasionally, text files have a bytesize of 36 or 0  instead
     of the proper bytesize of 7.  The -T flag forces these files
     to be considered as text files.

     Alternate tape devices or files may be specified with the -f
     flag.   The  special  filename  `-'  signifies  the standard

     On non-Berkeley Unix systems, name collisions can occur when
     the first 14 characters of extracted files are the same.  If
     this is the case, use the -n  <number>  option.   This  will
     cause  the  Unix  filenames to be numeric, starting with the
     number following the -n.   The  mapping  from  the  original
     TOPS-20 to the numeric Unix filenames is written to the file
     `` Logfile '' in the current directory.

     /dev/rmt8 - default tapefile.

     Jim Guyton, The Rand Corporation
     Jay Lepreau, University of Utah

     Files which span tape boundaries  are  handled  poorly.   To
     extract such a file, extract each piece and then combine the
     files under UNIX.

     Directory descriptor blocks on the tape are not interpreted.

     Offline files usually show up in directory listings  with  a
     zero bytesize.