LESSPIPE.SH(1)

User Commands

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 is 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, zlib 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, dmg, appimage and snap formats). Many other files will be reformatted for display. This includes pdf, dvi, markdown, Office (MS and OpenOffice) suite formats, NetCDF, matlab, device tree blob, html, xml and media (image, audio and video) formats. This requires helper programs to be 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, the text will be transformed using iconv into the default encoding. This assumes that the file command gets the file encoding right, which can be wrong in some situations. An appended colon to the file name suppresses 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 that the environment variable LESSOPEN is set properly. For ksh-like shells (bash, zsh), the command

LESSOPEN="|lesspipe.sh %s"; export LESSOPEN

activates 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 as described if the file name is lesspipe.sh. If it is installed under a different name, calling it without an argument will work as a filter with LESSQUIET set and expect 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, filtering in a pipe can however be forced by starting LESSOPEN with the characters |-.

If commands within lesspipe.sh fail, error messages are sometimes displayed; this is a considered buggy behavior and should be reported.

To suppress informal messages in the first line of the filter output, the environment 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 output was colorful, then the colon only disables the colorizer command. A second colon may then be required to display the original content. 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 and Perl POD formats 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, pod) follows, the output can be colorized (see also the section below).

Example: less index.html:html

If the xmq binary is installed, XML is rendered differently, so that the XML structure is easier to recognize. 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. The color scheme used is for a light background. To select the dark color scheme the ENV variable XMQ_THEME has to be set to the value dark.

OUTPUT COLORIZATION

The filter is able to do syntax highlighting for a wide variety of file types. It is not always wanted and can slow down the file display considerably. Therefore, an ENV variable LESS_MAXSIZE_COLOR (default: 200000) has been introduced. Larger files do not get colorized. If installed, nvimpager is used to colorize the output. If not, bat/batcat, pygmentize, e2ansi-cat, 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.

The contents of log files can be colorized if the tspin program is installed and the string ":log" is appended to the file name or the file extension is "log".

Among the colorizers, a preferred one can be forced by setting the environment 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: theme=ansi, style=plain

Syntax highlighting is activated if the environment variable LESS exists and contains the option -R, or if less is called with this option. This guarantees that escape sequences are 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, another one can be forced by appending a colon and a suffix to the file name. The list of suffixes and supported languages can be printed using the following colorizer commands:

bat --list-languages
batcat --list-languages
pygmentize -L lexers
M-x -mode [TAB] within emacs
source-highlight --lang-list
code2color -h
vimcolor -L (both for vimcolor and nvimpager)

In a pipe, that method cannot be used. As a workaround, a last argument can be added that is inspected by lesspipe.sh. A single colon (disengage filter) or :extension (force language) is possible, as in:

command that generates C code | less - :c

When the conditions for syntax highlighting are met, directory listings and listings of tar file contents are 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

For all plain text files not recognized as log files a colorizer is tried nevertheless as it sometimes can detect the correct file type and color the file aproppriately. This does however destroy the abilty to watch growing files using the F command within less. To retain the ability to watch growing files without the .log extension or when the log file colorizer tspin was called for log files, a single colon has to be given to the less call as the second argument as in:

less /var/log/syslog :

It can also be achieved by listing such files in a file .lessignore in the users home directory. The entries are fully specified path names or contain globbing characters. Such a file could look as follows:

syslog
*/syslog
*.syslog

This would allow watching growing files with the name syslog, all syslog files in arbitrary directories and all files with the ending .syslog.

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 in raw format, a colon (:) has to be appended to the file name. If it contains 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 file (for zsh and bash) and the _less (for zsh) and less (for bash) files generated during installation, 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 required for the completion algorithm are installed in directories according to the choices made during the installation (configure script).

The file lesscomplete has to be in one of the directories listed in $PATH and the function _less for zsh in a directory listed by $fpath. The file less with completion instructions for bash has to be sourced within a bash initialization script, e.g. in ~/.bashrc. New directories such as ~/scripts and ~/.fpath (for zsh) can be added using the commands

PATH=~/scripts:$PATH # (lesspipe.sh, less) fpath=(~/.fpath $fpath) # (_less, zsh only)

In zsh, compinit has to be called and the menucomplete option has to be set if it has not already been done. That can be achieved with the commands

autoload compinit
compinit -Uz
setopt menucomplete

In bash, bash-completion (usually a package with that name) has to be installed.

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 user's home directory) or lessfilter (and be accessible from a directory mentioned in $PATH). It has to be executable and must return 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, for example, to inhibit filtering for certain file types. A sample .lessfilter could look as follows:

#!/usr/bin/env bash

case $1 in
*.md|*.MD|*.mkd|*.markdown|*.rst)
# if the Python module rich.markdown is not found then
# the exit code is nonzero and lesspipe.sh is called
python3 -m rich.markdown -c $1 ;;
*.html|*.htm)
# call your favorite HTML beautifier, cat -b is just a boring example
cat -b $1 ;;
*)
exit 1;;
esac

AUTHOR

Wolfgang Friebel

REPORTING BUGS

Report bugs to <wp.friebel AT gmail DOT com> or open a github issue.