LESSPIPE.SH(1)

NAME
lesspipe.sh - a filter for less

SYNOPSIS
lesspipe.sh [FILE[s]]...

DESCRIPTION

The aim of lesspipe.sh is to enhance the output of less. The choice of the rules to be applied to modify the output are based on the file contents. The file extension is respected only as a last resort. Usually lesspipe.sh is called as an input filter to less.

With the help of that filter less will display the uncompressed contents of compressed (gzip, bzip2, compress, zstd, lz4, lzip, xz, lzma or brotli) files. For files containing archives and directories, a table of contents will be displayed (tar, ar, zip, 7-zip, rar, jar, cpio, rpm, deb ms-cabinet, iso, appimage and snap formats). Many other files will be reformatted for display. It includes pdf, dvi, markdown, Office (MS and Openoffice) suites formats, NetCDF, matlab, device tree blob, html, xml and media (image, audio and video) formats. This does require helper programs being installed.

The filter can also be applied recursively to extract and display files in archives on the fly. This works to a depth of 6 where applying a decompression algorithm counts as a separate level.

If the file utility reports text with an encoding different from the one used in the terminal then the text will be transformed using iconv into the default encoding. This does assume the file command gets the file encoding right, which can be wrong in some situations. An appended colon to the file name does suppress the conversion.

When using the programs git, vim or mutt they can be enabled to read non-text files by using lesspipe.sh. That is described in the Wiki at https://github.com/wofr06/lesspipe/wiki.

FILTER ACTIVATION
The filter is called from less provided the environment variable LESSOPEN is set properly. For ksh like shells (bash, zsh) the command
    LESSOPEN="|lesspipe.sh %s"; export LESSOPEN
does activate the filter for less. Use the fully qualified path, if lesspipe.sh is not in the search path. The command to set LESSOPEN can also be displayed by calling lesspipe.sh without arguments. This can even be used to set LESSOPEN directly:
    eval `lesspipe.sh` (bash) or
    lesspipe.sh|source /dev/stdin (zsh)
The above commands work only in the described manner if the file name is lesspipe.sh. If it is installed under a different name then calling it without an argument will work as a filter with LESSQUIET set and expecting input from STDIN.

Having set the environment variable as described above, less :will then display textual information for a wide range of file formats.

The filter is normally not called if input is piped to less as in
    cat somefile | less
As described in the man page of less, the filtering in a pipe can however be forced by starting LESSOPEN with the characters |-.

LESSOPEN starting with the two characters || to handle empty files and command errors is implemented only partly, usually on failures of commands within lesspipe.sh the error messages get displayed.

To suppress informal messages in the first line of the filter output the ENV variable LESSQUIET can be set to a nonempty value.

To disengage the filter temporarily a colon can be appended to the file name. If the file name contains a colon, then an equal sign should be used instead.

HTML, XML and Perl POD Files
Files in the html, xml and perl pod format are always rendered. Sometimes however the original contents of the file should be viewed instead. As mentioned before that can be achieved by appending a colon to the file name. If the correct file type (html, xml, pod) follows, the output can get colorized (see also the section below).

    Example: less index.html:html

If the binary xmq is installed, then xml is rendered differently, so that the xml structure is better recognized. A similar display for html contents using xmq is achieved by appending a colon to the file name. To get the original html file contents, two colons are required in this case.

OUTPUT COLORIZATION
The filter is able to do syntax highlighting for a wide variety of file types. If installed, nvimpager is used for colorizing the output. If not, bat/batcat, pygmentize, source-highlight, vimcolor and code2color are tried in turn. For bat/batcat the theme is set to ansi and the style is set to plain which comes closer to the unfiltered output of less. These settings can be changed in ~/.config/bat/config or by the environment variables BAT_STYLE and BAT_THEME.

Among the colorizers a preferred one can be forced for colorizing by setting the ENV variable LESSCOLORIZER to the name of the colorizer. For pygmentize and bat/batcat restricted option settings are allowed as follows:
    LESSCOLORIZER='pygmentize -O style=foo' (-P allowed as well)
    LESSCOLORIZER='bat --style=foo --theme=bar' (default is theme ansi, style plain)
Syntax highlighting is activated, if the environment variable LESS exists and contains the option -R or less is called with this option. This guarantees that escape sequences get converted into colors and do not garble the display. Using the option -r is not recommended, as the screen layout may be wrong, if long lines are in the output.

Syntax highlighting can be switched off by appending a colon after the file name, if the output was colorful. If the wrong language was chosen for syntax highlighting, then another one can be forced by appending a colon and a suffix to the file name.

In a pipe that method cannot be used. As a way out a last argument can be added that gets inspected by lesspipe.sh. A single colon (disengage filter) or :extension (force language) is possible as e.g with
    command that generates c code | less - :c

When the conditions for syntax highlighting are met directory listings and listings of tar file contents get colorized as well.

As less is used as a default browser in other programs (e.g. man, git, and perldoc)) lesspipe.sh may be engaged and alter the output of those programs.

WATCHING GROWING FILES
As soon as lesspipe.sh calls a program to convert the input the ability to watch growing files (using the F command within less) is lost. This is usually wanted for log files like syslog. To temporarily disengage lesspipe.sh a colon as the last argument for less needs to be added as e.g in
    less /var/log/syslog :
or less can be called with the +F argument, which is equivalent to F within the pager:
    less +F /var/log/syslog
Appending a colon to the file name does not work, as then the filter has to be engaged to at least remove that colon and use cat for the original file. On the other hand non growing log files can be colorized using ccze. Its recognition as a log file is difficult if not ending in .log but can be forced appending :.log to the file name as e.g in
    less /var/log/syslog:.log

ADVANCED USAGE
This version of lesspipe.sh allows you to view individual files contained in a file archive, which itself may even be contained in another archive.

The notation for viewing files in multifile archives is
    less archive_file:contained_file
or even
    less super_archive:archive_file:contained_file
To display the last file in the chain raw format, a colon (:) has to be appended to the file name. If it does contain a colon, then the alternate separator character equal sign (=) has to be used.

Again, this method of extracting and displaying files does not work if less is called in an output pipe and LESSOPEN starts with the |- characters. As already for syntax highlighting the solution is to use a second argument that starts with a colon. Then the above command would be written as
    cat super_archive | less - :archive:contained_file

COMPLETING MECHANISM FOR ARCHIVE CONTENTS
With the provided lesscomplete (for zsh and bash), _less (for zsh) and less_completion (for bash) files a tab completion for files in archives can be accomplished. Entering a colon (:) or an equal sign (=) after an archive file name and then pressing the tab key triggers the completion mechanism. This also works in chained archives. The files lesscomplete and less_completion have to be in one of the directories listed in $PATH and the function _less for zsh in a directory listed by $fpath. The less_completion script has to be sourced within a bash initialization script, e.g. in ~/.bashrc. New directories such as ~/scripts and ~/.fpath can be added using the commands
    PATH=~/scripts:$PATH and fpath=(~/.fpath $fpath)

USER DEFINED FILTERING
The lesspipe.sh filtering can be replaced or enhanced by a user defined program. Such a program has to be called either .lessfilter (and be placed in the users home directory), or lessfilter (and be accessible from a directory mentioned in $PATH). It has to be executable and has to end with an exit code 0, if the filtering was done within that script. Otherwise, a nonzero exit code means the filtering is left to lesspipe.sh.

This mechanism can be used to add filtering for new formats or e.g. inhibit filtering for certain file types.

AUTHOR
Wolfgang Friebel

REPORTING BUGS
Report bugs to <wp.friebel AT gmail DOT com>.

COPYRIGHT
Copyright © 2005-2024 Wolfgang Friebel
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
less(1)

A description of lesspipe.sh is also contained in the file README contained in the source code package