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    --nl=0                Disable newline
    --sp=~                Convert spaces to tilde
    --sp='OPEN BOX'       Unicode name
    --esc=+U+035B         Unicode code point

=head1 VERSION

Version 1.05

=head1 DESCRIPTION

The C<cat -v> command is often used to display characters that cannot
be displayed, but is not always suitable for viewing the output of
modern applications because it converts all non-ASCII characters.

The C<cat-v> command visualizes whitespace and control characters
while preserving the display of displayable graphic characters.

=begin html

<p><img width="750" src="https://raw.githubusercontent.com/tecolicom/App-cat-v/main/images/tree.png">

=end html

Also, by default, escape characters are not converted, so decorations
by ANSI escape sequences are retained.

=begin html

<p><img width="750" src="https://raw.githubusercontent.com/tecolicom/App-cat-v/main/images/visualized.png">

=end html

Sometimes it is desirable to visualize whitespace characters.  The
C<cat -t> command can visualize tab characters, but the problem is
that it breaks the visual format.  We may want to see which parts are
tabs and which parts are space characters while preserving the format.
Extra whitespace characters at the end of a line can also be noticed
by visualizing them.

Using C<cat-v>, tab characters are visualized in such a way that the
space on the display does not change.

=begin html

<p><img width="750" src="https://raw.githubusercontent.com/tecolicom/App-cat-v/main/images/tabstyle-needle.png">

=end html

Control characters can be displayed in control format and Unicode
symbol characters.  By default, control characters other than newline
and escape characters are displayed as corresponding Unicode symbols.

The second field is the default action. C<s> stands for symbol, C<m>
for Unicode mark, and C<0> for no conversion.

    nul   s  \000  \x{2400}  ␀  SYMBOL FOR NULL
    soh   s  \001  \x{2401}  ␁  SYMBOL FOR START OF HEADING
    stx   s  \002  \x{2402}  ␂  SYMBOL FOR START OF TEXT
    etx   s  \003  \x{2403}  ␃  SYMBOL FOR END OF TEXT
    eot   s  \004  \x{2404}  ␄  SYMBOL FOR END OF TRANSMISSION
    enq   s  \005  \x{2405}  ␅  SYMBOL FOR ENQUIRY
    ack   s  \006  \x{2406}  ␆  SYMBOL FOR ACKNOWLEDGE
    bel   s  \007  \x{2407}  ␇  SYMBOL FOR BELL
    bs    s  \010  \x{2408}  ␈  SYMBOL FOR BACKSPACE
    ht    s  \011  \x{2409}  ␉  SYMBOL FOR HORIZONTAL TABULATION
    nl    m  \012  \x{240A}  ␊  SYMBOL FOR LINE FEED
    vt    s  \013  \x{240B}  ␋  SYMBOL FOR VERTICAL TABULATION
    np    m  \014  \x{240C}  ␌  SYMBOL FOR FORM FEED
    cr    s  \015  \x{240D}  ␍  SYMBOL FOR CARRIAGE RETURN
    so    s  \016  \x{240E}  ␎  SYMBOL FOR SHIFT OUT
    si    s  \017  \x{240F}  ␏  SYMBOL FOR SHIFT IN
    dle   s  \020  \x{2410}  ␐  SYMBOL FOR DATA LINK ESCAPE
    dc1   s  \021  \x{2411}  ␑  SYMBOL FOR DEVICE CONTROL ONE
    dc2   s  \022  \x{2412}  ␒  SYMBOL FOR DEVICE CONTROL TWO
    dc3   s  \023  \x{2413}  ␓  SYMBOL FOR DEVICE CONTROL THREE
    dc4   s  \024  \x{2414}  ␔  SYMBOL FOR DEVICE CONTROL FOUR
    nak   s  \025  \x{2415}  ␕  SYMBOL FOR NEGATIVE ACKNOWLEDGE
    syn   s  \026  \x{2416}  ␖  SYMBOL FOR SYNCHRONOUS IDLE
    etb   s  \027  \x{2417}  ␗  SYMBOL FOR END OF TRANSMISSION BLOCK
    can   s  \030  \x{2418}  ␘  SYMBOL FOR CANCEL
    em    s  \031  \x{2419}  ␙  SYMBOL FOR END OF MEDIUM
    sub   s  \032  \x{241A}  ␚  SYMBOL FOR SUBSTITUTE
    esc   0  \033  \x{241B}  ␛  SYMBOL FOR ESCAPE
    fs    s  \034  \x{241C}  ␜  SYMBOL FOR FILE SEPARATOR
    gs    s  \035  \x{241D}  ␝  SYMBOL FOR GROUP SEPARATOR
    rs    s  \036  \x{241E}  ␞  SYMBOL FOR RECORD SEPARATOR
    us    s  \037  \x{241F}  ␟  SYMBOL FOR UNIT SEPARATOR
    sp    m  \040  \x{2420}  ␠  SYMBOL FOR SPACE
    del   s  \177  \x{2421}  ␡  SYMBOL FOR DELETE
    nbsp  s  \240  \x{2423}  ⍽  SHOULDERED OPEN BOX

At this time, Unicode markings are available for the following
characters

    nul   \x{2205}  ∅  EMPTY SET
    bel   \x{237E}  ⍾  BELL SYMBOL
    nl    \x{23CE}  ⏎  RETURN SYMBOL
    np    \x{2398}  ⎘  NEXT PAGE
    sp    \x{00B7}  ·  MIDDLE DOT
    esc   \x{21B0}  ↰  UPWARDS ARROW WITH TIP LEFTWARDS
    del   \x{232B}  ⌫  ERASE TO THE LEFT

=head1 OPTIONS

=over 7

=item B<-n>, B<--reset>

Disables all character conversions and tab expansion, and resets
repeat characters.  Therefore, the C<cat-v -n> effectively does
nothing, just like the C<cat> command.

Once the default behavior is reset, only options specified after it
will have any effect.  For example, the following command will only
visualize tab characters.

    cat-v -nt

=item B<-c>, B<--visible> I<name>=I<flag>,...