NAME

vis, inv − make unprintable characters in a file visible or invisible

SYNOPSIS

vis [ −n ] [ −s ] [ −u ] [ −w ] file ... 

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: HP

Native Language Support:
8−bit and 16−bit data, customs, messages.

DESCRIPTION

Vis reads characters from each file in sequence and writes them to the standard output, converting those which are not printable into a visible form.  Inv performs the inverse function, reading printable characters from each file and writing them, returned if appropriate to non-printable form, to standard out. 

Non-printable characters are represented using C-like escape conventions:

\\ backslash

\b backspace

\e escape

\f form-feed

\n new-line

\r carriage return

\s space

\t horizontal tab

\v vertical tab

\n the 8-bit character whose ASCII code is the 3-digit octal number n.

\xn the 8-bit character whose ASCII code is the 2-digit hexidecimal number n.

Space, horizontal tab, and new line may be treated as printable (and therefore passed unscathed to the output) or non-printable dependent on the options selected.  Backslash, although printable, is expanded by vis, to a pair of backslashes so that when passed back through inv, it can be mapped back to a single backslash.

If no input file is given, or if the argument − is encountered, vis and inv read from the standard input file. 

The options are:

−n causes new-line, space, and horizontal tab to be treated as non-printable characters.  Thus vis expands them visibly as \n, \s, and \t, rather passing them directly to the output.  Inv discards these character, expecting only the printable expansions.  New-line characters are inserted by vis every 16 characters so that the output will be in form acceptable for most editors. 

−s makes vis and inv silent about non-existent files, identical input and output, and write errors.  Normally, no input file may be the same as the output file unless it is a special file. 

−t treats horizontal tab and space as non-printable characters, in the same manner in which −n options treats them. 

−u causes output to be unbuffered (character-by-character); normally, output is buffered. 

−x causes vis output to be in hexidecimal form rather than the default octal form.  Either form is accepted to inv as input. 

EXAMPLE

If you encounter a file whose contents are unknown-perhaps binary or text-you can take a quick peek into it without jeopordizing your terminal:

vis -n file | head

This will safely show the first 160 bytes of the file. 

SEE ALSO

cat(1), echo(1), od(1). 

WARNING

Command formats such as

vis file1 file2 >file1

will cause the original data in file1 to be lost. 

Hewlett-Packard  —  last mod. May 11, 2021