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@(#) favorite trick for putting non-printables in scripts

 Most machines now have printf(1) put this information may still be handy


 If you actually type the  non-printable  characters  into a UNIX script
 you can cause  problems if you copy the file to a screen or printer, as
 some of the sequences might cause actions on the devices. Some mail 
 transmissions or editors may destroy or corrupt non-printable strings.
  
 The use of non-printable characters with echo(1) is not portable between
 various Unix implementations; and printf(1) is not always available. 

 A  very  portable  way  of  sticking  the  escape  character  into  the
 appropriate variable that avoids this problem follows.  As you can see,
 you get set up a lot of "non-printable" characters at once.

   #################
   #!/bin/sh
   set -a # start automatically exporting variables in Bourne shell
          # no lowercase letters in first string given to tr(1)
	  # make variable names in 'here' document all lowercase
   eval `tr '\[AM' '\033\001\015' <<\EOF
   esc=[
   soh=A
   cr=M
   EOF
   `
   set +a # stop automatically exporting variables in Bourne shell
   # you can now use the variables to generate 'nonprintable' strings.
   echo "${esc}2J"
   #################

 Now, for example, the variable esc contains an actual escape character.
 esc is the octal value 033.  Use lowercase for the variable names.  Use
 uppercase  for the letter to be converted so tr(1) does not  accidently
 convert a letter in the  variable  name.  I like to use the  characters
 that would  generate the desired  character  when used with the control
 key.

 UPDATE:
 Note  that  SOME  echo(1)  commands  will  let  you  put  non-printable
 characters in them using \octal_codes or other special sequences; that
 the printf command can do this;
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 Entering non-printable characters into a file using vi(1):

 To insert a  non-printable  character into a file or command when using
 vi, preceed the character  with a control-V.  Adding  carriage  returns
 and  escapes to a map command in your .exrc  files to define a function
 key is a common use of this feature.

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A safe way (other  than a dump with  od(1)) to display a file that might
contain non-printable  characters is to use the cat command with several
options:

   cat -v -e -t

On some  machines  -vet  will  work,  on  others  it will  not.  On some
machines the -v option must be present or the -t and -e options will not
work. The most restrictive behavior is something like:

-v   Cause non-printing characters except tabs, new-lines and form-feeds
     to be printed.
       o  Control  characters  are printed  using the form ^X (Ctrl-X)
       o  the DEL  character  (octal 0177) is printed as ^?.
       o  Other  non-printing  characters are printed as M-x, where x is
          the character specified by the seven low order bits.

     When the -v option is used these options are also available:

        -e   Print a $ character at the end of each line.  This lets you
             see trailing  white  space,  which  sometimes  is causing a
             problem.

        -t   Print each tab character as ^I.  

On some  systems  (HP-UX,  for  one)  commands  called  vis and  inv are
available for a somewhat similiar purpose.
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