Text vs. Non-Text vs. PostScript

1. Text vs. Non-Text

Text files, also referred to as plain text or ASCII, consists of normal words/numbers/punctuation. You can edit such files with the simplest text editors (vi, emacs, pico, nedit). Email messages are text, Fortran source code is text, shell scripts are text, even the following ``ASCII art'' is text;

      _____         .    _  .
     /#  /_\_       |\_|/__/|
    |   |/o\o\     / / \/ \  \
    |   \\_/_/    /__|o||o|__ \
   /  |_   |    |/_  \_/\_/ _\ |
  |   ||\_ ~|   | |  (____) | ||
  |   ||| \/    \/\____/\__/  //
  |   |||_      (_/          ||
   \_//  |       |           ||
     ||  |       |           ||\
     ||_  \       \         //_/
     \_|  o|       \_______//
     /\___/        __ || __||
    /  ||||__     (____(____)
      (____)_)    /***********\
     ----------------------
      Happy Happy Joy Joy

In short, if you can type it on a keyboard or typewriter, it's text.

The following image is NOT text;

nor is the file ``a.out'' that I get when compiling a C++ or Fortran program. Such nontext files are also called binary files.

Here's what you do with a plain text file;

You can email it in unchanged form
Display its contents on the terminal using more or cat
Edit its contents using vi or pico or emacs or nedit
Scan its contents for a certain phrase using grep, e.g., grep "diagonal matrix" thesis.txt
Print it using enscript

2. PostScript Files

PostScript files are, strictly speaking, text files, but a special kind of text file containing commands in the PostScript page-description language. Unless you learn the PostScript language, the contents of such a file may bewilder you; however, here are some simple tips.

PostScript files should be named with the suffix .ps or .eps (but Unix doesn't enforce naming rules).
PostScript files always begin, on the very top line, with the two characters %!. This is how a printer knows that the text in the remainder of the file should be interpreted according to the rules of PostScript
Rather than view the textual contents of a PostScript file, use ghostview to view the page/graphic which the PostScript commands describe, e.g., ghostview graph.ps
Print it using lp, unless it is ``encapsulated'' PostScript (the latter is intended only for inclusion in documents)
Edit it only if you have sufficient understanding of the PostScript language. PostScript files are usually generated by word processing or graphics programs rather than by hand, so they tend to be unfriendly to the would-be human text-editor.

3. Non-Text Files

Non-text or binary files, neither plain text nor PostScript, cannot be printed directly. Many binary files, like compiled programs or audio files, do not have visual content and are never intended to be printed. Others, like image files in JPG or PNG format, can only be printed from within graphics/viewing software, unless they are explicitly converted to PostScript and the resulting file printed with the lp command.

JPEG and PNG images can be converted to PostScript, on Unix computers, by commands like convert or xv. Also, heavy-duty software like IDL or Mathematica or Matlab can read and display images from JPG and PNG files; from there you can convert and/or print according to that software's usual methods.