@c $Id: viewing-text.texinfo,v 1.32 2001/06/04 15:29:21 m Exp m $
@node    Viewing Text, Text Editing, Text, Text
@comment node-name,     next,   previous,       up
@chapter Viewing Text
@cindex viewing text

@noindent
Dealing with textual matter is the meat of Linux (and of most
computing), so there are going to be many chapters about the various
aspects of text. This first chapter in this part of the book shows how
to @emph{view} text on your display screen.

There are many ways to view or otherwise output text. When your
intention is to edit the text of a file, open it in a text editor, as
described in @ref{Text Editing, , Text Editing}.

Some kinds of files---such as PostScript, DVI, and PDF files---often
contain text in them, but they are technically not text files. These are
image format files, and I describe methods for viewing them in
@ref{Print Preview, , Previewing Print Files}.

@sp .25
@noindent
@strong{NOTE:} To learn how to browse files and their contents in a Web
browser, see @ref{Browsing Files, , Browsing Files}.

@menu
* Perusing Text::               Perusing text on the display.
* Outputting Text::             Outputting part of a text file.
* Streaming Text::              Reading a stream of text.
* ASCII Chart::                 Viewing a character chart.
@end menu


@node Perusing Text, Outputting Text, Viewing Text, Viewing Text
@comment  node-name,  next,  previous,  up
@section Perusing Text
@cindex perusing text
@cindex text, perusing
@pindex less
@pindex zless
@pindex more

@noindent
Use @code{less} to peruse text, viewing it one screen (or ``page'') at
a time. The @code{less} tool works on either files or standard
output---it is popularly used as the last command on a pipeline so that
you can page through the text output of some commands. For an example, see
@ref{Pipelines, , Redirecting Output to Another Command's Input}.

@code{zless} is identical to @code{less}, but you use it to view
compressed text files; it allows you to read a compressed text file's
contents without having to uncompress it first (@pxref{File Compression,
, Compressed Files}). Most of the system documentation in the
@file{/usr/doc} and @file{/usr/share/doc} directories, for example,
consists of compressed text files.

You may, on occasion, be confronted with a reference to a command for
paging text called @code{more}. It was the standard tool for paging text
until it gave way to @code{less} in the early to mid-1990s; @code{less}
comes with many more options---its most notable advantage being the
ability to scroll @emph{backward} through a file---but at the expense of
being almost exactly three times the size of @code{more}. Hence there
are two meanings to the saying, ``less is more.''

@menu
* Perusing File::               Perusing a file.
* Perusing Multiple Files::     Perusing many files at once.
* Less Options::                Keystroke commands while you peruse.
@end menu


@node Perusing File, Perusing Multiple Files, Perusing Text, Perusing Text
@comment  node-name,  next,  previous,  up
@subsection Perusing a Text File
@cindex perusing a text file
@cindex paging through a file
@cindex file, perusing a text

@noindent
To peruse or page through a text file, give the name of the file as an
argument to @code{less}.

@itemize @bullet
@item
To page through the text file @file{README}, type:

@example
$ @kbd{less README @key{RET}}
@end example
@end itemize

This command starts @code{less} and displays the file @file{README} on
the screen.

You can more forward through the document a line at a time by typing
@kbd{@key{@math{@downarrow}}}, and you can move forward through the
document a screenful at a time by typing @kbd{@key{PgDn}}. To move
backward by a line, type @key{@math{@uparrow}}, and type
@kbd{@key{PgUp}} to move backward by a screenful.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the <- and/or -> arrow keys.]
@end ifinfo

You can also search through the text you are currently perusing---this
is described in @ref{Less Search, , Searching Text in Less}.

To stop viewing and exit @code{less}, press @kbd{@key{Q}}.


@node Perusing Multiple Files, Less Options, Perusing File, Perusing Text
@comment  node-name,  next,  previous,  up
@subsection Perusing Multiple Text Files
@cindex perusing multiple text files
@cindex paging through multiple files
@cindex files, perusing multiple text

@noindent
You can specify more than one file to page through with @code{less}, and
you can specify file patterns in order to open all of the files that
match that pattern.

@itemize @bullet
@item
To page through all of the Unix FAQ files in @file{/usr/doc/FAQ}, type:

@example
$ @kbd{less /usr/doc/FAQ/unix-faq-part* @key{RET}}
@end example
@end itemize

This command starts @code{less}, opens in it all of the files that
match the given pattern @samp{/usr/doc/FAQ/unix-faq-part*}, and begins
displaying the first one:

@cartouche
@image{viewing-text-less-01, 4 in}
@end cartouche

@sp .25
@noindent
@strong{NOTE:} When you specify more than one file to page, @code{less}
displays each file in turn, beginning with the first file you specify or
the first file that matches the given pattern. To move to the next file,
press @kbd{@key{N}}; to move to the previous file, press @kbd{@key{P}}.


@node Less Options, , Perusing Multiple Files, Perusing Text
@comment  node-name,  next,  previous,  up
@subsection Commands Available While Perusing Text
@cindex commands available while perusing text
@cindex perusing text, commands available while 
@pindex less

@noindent
The following table gives a summary of the keyboard commands that you
can use while paging through text in @code{less}. It lists the
keystrokes and describes the commands.

@multitable @columnfractions .30 .70
@item @sc{Keystroke}
@tab @sc{Command}
@item @key{@math{@uparrow}}
@tab Scroll back through the text (``up'') one line.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the <- and/or -> arrow keys.]
@end ifinfo

@item @key{@math{@downarrow}}
@tab Scroll forward through the text (``down'') one line.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the <- and/or -> arrow keys.]
@end ifinfo

@item @key{@math{@leftarrow}} @var{or} @key{@math{@rightarrow}}
@tab Scroll horizontally (left or right) one tab stop; useful for
perusing files that contain long lines.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the <- and/or -> arrow keys.]
@end ifinfo

@item @key{PgUp} @var{or} @key{SPC}
@tab Scroll forward through the text by one screenful.

@item @key{PgDn}
@tab Scroll backward through the text by one screenful.

@item @code{C-l}
@tab Redraw the screen.

@item @code{/@var{pattern}}
@tab Search forward through the file for lines containing
@var{pattern}.

@item @code{?@var{pattern}}
@tab Search backward through the file for lines containing
@var{pattern}.

@item @code{<}
@tab Move to beginning of the file.

@item @code{>}
@tab Move to end of the file.

@item @code{h}
@tab Display a help screen.

@item @code{q}
@tab Quit viewing the file and exit @code{less}.
@end multitable


@node Outputting Text, Streaming Text, Perusing Text, Viewing Text
@comment  node-name,  next,  previous,  up
@section Outputting Text
@cindex outputting text
@cindex text, outputting
@pindex cat

@noindent
The simplest way to view text is to output it to standard output. This
is useful for quickly looking at part of a text, or for passing part of
a text to other tools in a command line.

Many people still use @code{cat} to view a text file, especially if it
is a very small file. To output all of a file's contents on the screen,
use @code{cat} and give the file name as an argument.

This isn't always the best way to peruse or read text---a very large
text will scroll off the top of the screen, for example---but sometimes
the simple outputting of text is quite appropriate, such as when you
just want to output one line of a file, or when you want to output
several files into one new file.

This section describes the tools used for such purposes. These tools are
best used as filters, often at the end of a pipeline, outputting the
standard input from other commands.

@sp .25
@noindent
@strong{NOTE:} Tools and methods for outputting text for printing, such
as outputting text in a font, are described in @ref{Enscript, ,
Converting Plain Text for Output}.

@menu
* Nonprinting Text::            Showing non-printing characters.
* Beginning Output::            Output the beginning part of a text.
* Ending Output::               Output the ending part of a text.
* Middle Output::               Output the middle part of a text.
* String Output::               Output the text between strings.
* Dialect Output::              Output text in a dialect.
@end menu


@node Nonprinting Text, Beginning Output, Outputting Text, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Showing Non-printing Characters
@cindex showing non-printing characters
@cindex non-printing characters, showing
@cindex control characters, showing
@cindex lines, showing the ends of
@cindex tab characters, showing
@cindex hat notation
@pindex cat

@noindent
Use @code{cat} with the @samp{-v} option to output non-printing
characters, such as control characters, in such a way so that you can
see them. With this option, @code{cat} outputs those characters in
@dfn{hat notation}, where they are represented by a @samp{^} and the
character corresponding to the actual control character (for example, a
bell character would be output as @samp{^G}).

@itemize @bullet
@item
To peruse the file @file{translation} with non-printing characters
displayed in hat notation, type:

@example
$ @kbd{cat -v translation | less @key{RET}}
@end example
@end itemize

In this example, the output of @code{cat} is piped to @code{less} for
viewing on the screen; you could have piped it to another command, or
redirected it to a file instead.

To visually display the end of each line, use the @samp{-E} option; it
specifies that a @samp{$} should be output after the end of each line.
This is useful for determining whether lines contain trailing space
characters.

Also useful is the @samp{-T} option, which outputs tab characters as
@samp{^I}. 

The @samp{-A} option combines all three of these options---it is the
same as specifying @samp{-vET}.


@node Beginning Output, Ending Output, Nonprinting Text, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Outputting a Beginning Part of a Text
@cindex outputting a beginning part of a text
@cindex text, outputting a beginning part of a 
@pindex head

@noindent
Use @code{head} to output the beginning of a text. By default, it
outputs the first ten lines of its input.

@itemize @bullet
@item
To output the first ten lines of file @file{placement-list}, type:

@example
$ @kbd{head placement-list @key{RET}}
@end example
@end itemize

You can specify as a numeric option the number of lines to output. If
you specify more lines than a file contains, @code{head} just outputs
the entire text.

@itemize @bullet
@item
To output the first line of file @file{placement-list}, type:

@example
$ @kbd{head -1 placement-list @key{RET}}
@end example

@item
To output the first sixty-six lines of file @file{placement-list}, type:

@example
$ @kbd{head -66 placement-list @key{RET}}
@end example
@end itemize

To output a given number of @emph{characters} instead of lines, 
give the number of characters to output as an argument to the @samp{-c}
option.

@itemize @bullet
@item
To output the first character in the file @file{placement-list}, type:

@example
$ @kbd{head -c1 placement-list @key{RET}}
@end example
@end itemize


@node Ending Output, Middle Output, Beginning Output, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Outputting an Ending Part of a Text
@cindex outputting an ending part of a text
@cindex text, outputting an ending part of a 
@pindex tail
@pindex less

@noindent
The @code{tail} tool works like @code{head}, but outputs the last part
of its input. Like @code{head}, it outputs ten lines by default.

@itemize @bullet
@item
To output the last ten lines of file @file{placement-list}, type:

@example
$ @kbd{tail placement-list @key{RET}}
@end example

@item
To output the last fourteen lines of file @file{placement-list}, type:

@example
$ @kbd{tail -14 placement-list @key{RET}}
@end example
@end itemize

It is sometimes useful to view the end of a file on a continuing basis;
this can be useful for a ``growing'' file, a file that is being written
to by another process. To keep viewing the end of such a file, use
@code{tail} with the @samp{-f} (``follow'') option. Type @kbd{C-c} to
stop viewing the file.

@itemize @bullet
@item
To follow the end of the file @file{access_log}, type:

@example
$ @kbd{tail -f access_log @key{RET}}
@end example
@end itemize

@sp .25
@noindent
@strong{NOTE:} You can achieve the same result with @code{less}; to do
this, type @kbd{F} while perusing the text (@pxref{Perusing Text, ,
Perusing Text}).


@node Middle Output, String Output, Ending Output, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Outputting a Middle Part of a Text
@cindex outputting a middle part of a text
@cindex text, outputting a middle part of a
@pindex head
@pindex tail
@pindex sed

@noindent
There are a few ways to output only a middle portion of a text.

To output a particular line of a file, use the @code{sed} tool
(@pxref{Stream Editing, , Editing Streams of Text}).  Give as a quoted
argument the line number to output followed by @samp{!d}. Give the file
name as the second argument.

@itemize @bullet
@item
To output line 47 of file @file{placement-list}, type:

@example
$ @kbd{sed '47!d' placement-list @key{RET}}
@end example
@end itemize

To output a region of more than one line, give the starting and ending
line numbers, separated by a comma.

@itemize @bullet
@item
To output lines 47 to 108 of file @file{placement-list}, type:

@example
$ @kbd{sed '47,108!d' placement-list @key{RET}}
@end example
@end itemize

You can also combine multiple @code{head} or @code{tail} commands on a
pipeline to get the desired result (@pxref{Pipelines, , Redirecting
Output to Another Command's Input}).

@itemize @bullet
@item
To output the tenth line in the file @file{placement-list}, type:

@example
$ @kbd{head placement-list | tail -1 @key{RET}}
@end example

@item
To output the fifth and fourth lines from the bottom of file
@file{placement-list}, type:

@example
$ @kbd{tail -5 placement-list | head -2 @key{RET}}
@end example

@item
To output the 500th character in @file{placement-list}, type:

@example
$ @kbd{head -c500 placement-list | tail -c1 @key{RET}}
@end example

@item
To output the first character on the fifth line of the file
@file{placement-list}, type:

@example
$ @kbd{head -5 placement-list | tail -1 | head -c1 @key{RET}}
@end example
@end itemize

In the preceding example, three commands were used: the first five lines
of the file @file{placement-list} are passed to @code{tail}, which
outputs the last line in the output (the fifth line in the file); then,
the last @code{head} command outputs the first character in that last
line, which achieves the desired result.


@node String Output, Dialect Output, Middle Output, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Outputting the Text between Strings
@cindex outputting the text between strings
@cindex text, outputting that between strings
@cindex strings, outputting the text between
@pindex sed

@noindent
Use @code{sed} to select lines of text between strings and output either
just that section of text, or all of the lines of text @emph{except}
that section. The strings can be words or even regular expressions
(@pxref{Regexps, , Regular Expressions---Matching Text Patterns}).

Use the @samp{-n} option followed by
@samp{'/@var{first}/,/@var{last}/p'} to output just the text between the
strings @var{first} and @var{last}, inclusive. This is useful for
outputting, say, just one chapter or section of a text file when you
know the text used to begin the sections with.

@itemize @bullet
@item
To output all the text from file @file{book-draft} between @samp{Chapter
3} and @samp{Chapter 4}, type:

@example
$ @kbd{sed -n '/Chapter 3/,/Chapter 4/p' book-draft @key{RET}}
@end example
@end itemize

To output all of the lines of text @emph{except} those between two
patterns, omit the @samp{-n} option.

@itemize @bullet
@item
To output all the text from file @file{book-draft}, except that which
lies between the text @samp{Chapter 3} and @samp{Chapter 4}, type:

@example
$ @kbd{sed '/Chapter 3/,/Chapter 4/p' book-draft @key{RET}}
@end example
@end itemize

@sp .25
@noindent
@strong{NOTE:} For a more thorough introduction to @code{sed}, see
@ref{Stream Editing, , Editing Streams of Text}.


@need 1500
@node Dialect Output, , String Output, Outputting Text
@comment  node-name,  next,  previous,  up
@subsection Outputting Text in a Dialect
@cindex outputting text in a dialect
@cindex dialects, outputting text in
@cindex text, outputting in a dialect
@cindex filter, defined
@cindex Orwell, George
@cindex @cite{1984}
@pindex filters
@pindex kraut
@pindex cat

@flushleft
@sf{Debian}: @file{filters}
@sf{WWW}: @url{http://www.princeton.edu/~mkporwit/pub_links/davido/slang/}
@sf{WWW}: @url{http://www.mathlab.sunysb.edu/~elijah/src.html}
@end flushleft
@*
@noindent
There are all kinds of tools that work as filters on text; this recipe
describes a specific group of filters---those that filter their standard
input to give the text an accent or dialect, and are intended to be
humorous.

Generally speaking, a @dfn{filter} is a tool that works on standard
input, changing it in some way, and then passing it to standard output.

@itemize @bullet
@item
To apply the @code{kraut} filter to the text in the file
@file{/etc/motd}, type:

@example
$ @kbd{cat /etc/motd | kraut @key{RET}}
@end example
@end itemize

These commands pass the contents of the file @file{/etc/motd} to the
@code{kraut} filter, whose output is then sent to standard output. The
contents of @file{/etc/motd} are not changed.

Some of the dialect filters available include @code{nyc}, which gives a
``New Yawker'' dialect to text, and @code{newspeak}, which translates
text into the approved language of the thought police, as described in
George Orwell's novel, @cite{1984}. Hail Big Brother!


@node Streaming Text, ASCII Chart, Outputting Text, Viewing Text
@comment  node-name,  next,  previous,  up
@section Streaming Text
@cindex streaming text
@cindex text, streaming
@cindex RSVP
@cindex rapid serial visual presentation (RSVP)
@pindex sview

@flushleft
@sf{WWW}: @url{http://www.maurer-it.com/open-source/sview/}
@end flushleft
@*
@noindent
It's been demonstrated that people read and comprehend printed text
faster than they read and comprehend text displayed on a computer
display screen. Rapid serial visual presentation, or RSVP, is a
technique that aims to increase reading speed and comprehension with the
use of computer display screens. With this technique, text is displayed
@emph{streamed} on the screen, one word at a time, with pauses between
words and punctuation. The average reading time is lowered and
comprehension is increased significantly with this technique.

GNOME @code{sview} is a ``streaming viewer'' for X; it streams text a
word at a time on the screen, at a default rate of 450 words per
minute. Use it to read text files and the X selection, which is text you
have selected with the mouse (@pxref{Selecting Text, , Selecting Text}).

To open a file in @code{sview}, either specify it as an argument to the
command, or choose @code{Open} from the @code{File} menu in
@code{sview}, and select the file from there.

@itemize @bullet
@item
To view the contents of the text file @file{alice-in-wonderland} in
@code{sview}, type:

@example
$ @kbd{sview alice-in-wonderland @key{RET}}
@end example
@end itemize

To start streaming the text, either press @key{S} once, or left-click on
the button marked RSVP. Both @key{S} and the RSVP button toggle the
streaming; the left and right arrow keys control the speed.

Text being streamed with @code{sview} looks like this:

@image{viewing-text-sview-01, 4 in}

The large area with the word @samp{beginning} in it is where the text is
being streamed. The text in the lower-left window is a shrunken view of
the entire file, the text in the lower-right window is the paragraph
from which the current word comes from.

To open another file, choose it from the menu; you can have many files
open in @code{sview} at once. @code{sview} places each file in its own
buffer. You can also paste the X selection into a buffer of its own---to
switch to a different buffer, choose its name from the @code{Buffer}
menu.

Type @key{Q} to quit reading and exit @code{sview}.

The following table lists the keyboard commands used in @code{sview} and
describes their meaning.

@multitable @columnfractions .30 .70
@item @sc{Keystroke}
@tab @sc{Description}
@item @code{@key{@math{@leftarrow}}}
@tab Decrease the stream speed.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the <- arrow key.]
@end ifinfo

@item @code{@key{@math{@rightarrow}}}
@tab Increase the stream speed.
@ifinfo
[GNU INFO BUG: any <> in the preceding line should be the -> arrow key.]
@end ifinfo

@item @code{C-o}
@tab Open a file.

@item @code{C-q}
@tab Quit viewing text and exit @code{sview}.

@item @code{C-w}
@tab Erase the current text buffer.

@item @code{M-n}
@tab Move forward to the next word.

@item @code{M-p}
@tab Move backward to the previous word.

@item @code{@key{S}}
@tab Toggle the streaming of text.

@item @code{@key{X}}
@tab Display the X selection in its own buffer.

@item @code{@key{N}}
@tab Move forward to the next paragraph.

@item @code{@key{P}}
@tab Move backward to the previous paragraph.
@end multitable


@node ASCII Chart, , Streaming Text, Viewing Text
@comment  node-name,  next,  previous,  up
@section Viewing a Character Chart
@cindex viewing a character chart
@cindex character chart, viewing a
@cindex special characters, listing
@cindex ASCII character chart, viewing
@cindex ISO 8859-1 character set
@pindex ascii
@pindex man

@noindent
To view a character chart containing a list of all the valid characters
in the ASCII character set and the character codes to use to type them,
view the @code{ascii} @code{man} page.

@itemize @bullet
@item
To view an ASCII character set, type:

@example
$ @kbd{man ascii @key{RET}}
@end example
@end itemize

You can use the octal codes listed for each character to type them in
Emacs---see @ref{Emacs Inserts, , Inserting Special Characters in
Emacs}.

The default Linux character set, the ISO 8859-1 (``Latin 1'') character
set, contains all of the standard ASCII character set plus an additional
128 characters.

To view the ISO 8859-1 character set, which contains an extended set of
characters above the standard 127 ASCII characters, view the
@code{iso_8859_1} @code{man} page.

@itemize @bullet
@item
To view the ISO 8859-1 character set, type:

@example
$ @kbd{man iso_8859_1 @key{RET}}
@end example
@end itemize

You can use this page to see all of the characters in this character set
and how to input them.

@sp .25
@noindent
@strong{NOTE:} There's a special way to ``quote'' these characters in
Emacs; this technique is described in @ref{Emacs Inserts, , Inserting
Special Characters in Emacs}.

The @file{miscfiles} package also contains charts for these character
sets, as explained in @ref{Reference Files, , Word Lists and Reference
Files}.