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lesspipe.sh, a preprocessor for less

Version: 2.16 Author : Wolfgang Friebel wp.friebel@gmail.com License: GPL

Latest version available as: zip file on github and the repository on github

The development version can be cloned using git: git clone https://github.com/wofr06/lesspipe.git To report bugs or make proposals to improve lesspipe please contact the author by email.

Contents

  1. Motivation
  2. Introduction
  3. Usage
  4. Required programs
  5. Supported file formats
    • Supported compression methods and archive formats
    • List of preprocessed file types
    • Conversion of files with alternate character encoding
  6. Colorizing the output
    • Syntax highlighting
      • Syntax highlighting choices
      • List of supported languages
    • Colored Directory listing
    • Colored listing of tar file contents
  7. Calling less from standard input
  8. Displaying files with special characters in the file name
  9. Tab completion for zsh and bash
  10. User defined filtering
  11. Debugging
  12. (Old) documentation about lesspipe
  13. External links - URLs to some utilities - References
  14. Contributors

0. Motivation

If you use

  • the pager less in the command line,
  • the version control system git,
  • the text editor Vim or
  • the mail client mutt,

then lesspipe.sh enables these programs to read non-text files, such as:

  • PDFs,
  • (Microsoft or LibreOffice) Office documents, or even
  • media (such as JPG or PNG images, MP3 audio or video) files

where read means,

  • (format and) show the contained text (of a document or tag in a media file), or
  • show sensible file information (such as length of the video).

To enable less respectively git, Vim or mutt to read non-text files by lesspipe.sh, see

For the text and info extraction, lesspipe.sh will depend on external tools, but many use cases are covered by an installation of

  • LibreOffice and a common text browser (such as lynx),
  • pdftotext, and
  • mediainfo (or exiftool).

1. Introduction

To browse files under UNIX the excellent viewer less [1] can be used. By setting the environment variable LESSOPEN, less can be enhanced by external filters to become even more powerful. Most Linux distributions come already with a "lesspipe.sh" that covers the most common situations.

The input filter for less described here is called "lesspipe.sh". It is able to process a wide variety of file formats. It enables users to deeply inspect archives and to display the contents of files in archives without having to unpack them before. That means file contents can be properly interpreted even if the files are compressed and contained in a hierarchy of archives (often found in RPM or DEB archives containing source tarballs). The filter is easily extensible for new formats.

The input filter which is also called "lesspipe.sh" is a bash script, but works as well as a zsh script.

The filter does different things depending on the file format. In most cases it is determined on the output of the file --mime command [2], that returns the mime type. In some cases the mime type is too unspecific and then the file command yielding a textual description or the file suffix is used to determine what to display.

By default less wraps long lines unless called with the option -S or --chop-long-lines. That can be changed interactively by typing -S followed by ENTER when viewing files with long lines. It is e.g. quite useful for tabular display of csv files with many columns.

2. Usage

(see also the man page lesspipe.1)

To activate lesspipe.sh the environment variable LESSOPEN has to be defined in the following way:

        LESSOPEN="|lesspipe.sh %s"; export LESSOPEN  # (sh like shells)
        setenv LESSOPEN "|lesspipe.sh %s"            # (csh, tcsh)

If lesspipe.sh is not in the UNIX search path or if the wrong lesspipe.sh is found in the search path, then the full path to lesspipe.sh should be given in the above commands. 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.

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)

Several Linux distributions do now set LESSOPEN by default and if the contents of the variable is not referring to this lesspipe.sh version, it has to be redefined to get the functionality described here.

As lesspipe.sh is accepting only a single argument, a hierarchical list of file names has to be separated by a non-blank character. A colon is rarely found in file names, therefore it has been chosen as the separator character. If a file name does however contain at least one isolated colon, the equal sign = can be used as an alternate separator character. At each stage in extracting files from such a hierarchy, the file type is determined. This guarantees a correct processing and display at each stage of the filtering.

To view files in archives, the following command can be used:

        less archive_file:contained_file

This can be used to extract files from an archive:

        less archive_file:contained_file > extracted_file

For extracting files less is not required, that can be done also using:

        lesspipe.sh archive_file:contained_file > extracted_file

Even a file in an archive, that itself is contained in yet another archive can be viewed this way:

        less super_archive:archive_file:contained_file

The script is able to extract files up to a depth of 6 where applying a decompression algorithm counts as a separate level. In a few rare cases, the file command does not recognize the correct format. In such cases, the filtering can be suppressed by a trailing colon on the file name. That can also be used to output the original unmodified file or to suppress syntax highlighting (see below).

Several environment variables can influence the behavior of lesspipe.sh.

LESSQUIET will suppress additional output not belonging to the file contents if set to a non-empty value.

LESS can be used to switch on colored less output (should contain -R).

LESSCOLORIZER can be set to prefer a highlighting program from the following choices (nvimpager bat batcat pygmentize source-highlight vimcolor code2color). Otherwise the first program in that list that is installed will be used, with the caveat that bat will use ansi theme instead of its default colors.

3. Required programs

Most of the programs are checked for its existence before they get called in lesspipe.sh. However some of the programs are assumed to always be installed. That is foremost bash or zsh (have the appropriate first line in the script), then file and other utilities like cat, grep, ln, ls, mkdir, rm, strings, tar and tr. For testing lesspipe.sh perl is used, that is however not required in just using lesspipe.sh.

4. Supported file formats

Currently lesspipe.sh [3] supports the following compression methods and file types (i.e. the file contents gets transformed by lesspipe.sh):

4.1 Supported compression methods and archive formats

  • gzip, compress requires gzip
  • bzip2 requires bzip2
  • lzma requires lzma or 7z
  • xz requires xz or 7z
  • zstd requires zstd
  • brotli requires bro
  • lz4 requires lz4
  • tar requires optionally archive_color for colorizing
  • ar library requires bsdtar or ar
  • zip archive requires bsdtar or unzip
  • jar archive requires bsdtar or unzip
  • rar archive requires bsdtar or unrar or rar
  • 7-zip archive requires 7zz or 7zr or 7z or 7za
  • lzip archive requires lzip
  • iso images requires bsdtar or isoinfo or 7z
  • rpm requires rpm2cpio and cpio or bsdtar
  • Debian requires bsdtar or ar
  • cab requires cabextract or 7z
  • cpio requires cpio or bsdtar or 7z
  • appimage requires unsquashfs
  • snap requires snap and unsquashfs

4.2 List of preprocessed file types

  • directory displayed using ls -lA
  • nroff(man) requires mandoc or man or groff
  • shared library requires nm
  • MS Word (doc) requires wvText or catdoc or libreoffice
  • Powerpoint (ppt) requires catppt
  • Excel (xls) requires in2csv (csvkit) or xls2csv
  • odt requires pandoc or odt2txt or libreoffice
  • odp requires libreoffice
  • ods requires xlscat or libreoffice
  • MS Word (docx) requires pandoc or docx2txt or libreoffice
  • Powerpoint (pptx) requires pptx2md or libreoffice
  • Excel (xlsx) requires in2csv or xlscat or excel2csv or libreoffice
  • csv requires csvtable or csvlook or column or pandoc
  • rtf requires unrtf or libreoffice
  • epub requires pandoc
  • html,xml requires one of xmq, w3m, lynx, elinks or html2text
  • pdf requires pdftotext or pdftohtml
  • perl pod requires pod2text or perldoc
  • dvi requires dvi2tty
  • djvu requires djvutxt
  • ps requires ps2ascii (from the gs package)
  • mp3 requires id3v2
  • multimedia formats requires mediainfo or exiftools
  • image formats requires mediainfo or exiftools or identify
  • hdf, nc4 requires h5dump or ncdump (NetCDF format)
  • crt, pem, csr, crl requires openssl
  • matlab requires matdump
  • Jupyter notebook requires pandoc
  • markdown requires mdcat or pandoc
  • log requires ccze
  • java.class requires procyon
  • MacOS X plist requires plistutil
  • binary data requires strings
  • json requires jq
  • device tree blobs requires dtc (extension dtb or dts)

Files in the html, xml and perl pod format are always rendered. Sometimes however the original contents of the file should be viewed instead. 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).

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.

4.3 Conversion of files with alternate character encoding

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.

5. Colorizing the output

Syntax highlighting and other methods of colorizing the output is only activated if the environment variable LESS is existing and contains the option -R (or -r) or less is called with one of these options.

The display of wrapped long lines and moving backward in a file using the option -r can give weird output and is not recommended. For an explanation see http://www.greenwoodsoftware.com/less/faq.html#dashr

5.1 Syntax highlighting

Syntax highlighting is not always wanted, it can be switched off by appending a colon after the file name. If the wrong language was chosen for syntax highlighting or no language was recognized, then the correct one can be forced by appending a colon and a suffix to the file name as follows (assuming plfile is a file with perl syntax):

        less plfile:pl or less plfile:perl (depending on the colorizer)

5.1.1 Syntax highlighting choices

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, code2color and vimcolor are tried. Among these 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 a restricted set of options can be added:

        LESSCOLORIZER='pygmentize -O style=foo'
        LESSCOLORIZER='bat --style=foo --theme=bar' # --theme=default for default theme

Much better syntax highlighting is obtained using the less emulation of vim: The editor vim comes with a file less.sh, e.g. on Ubuntu located in /usr/share/vim/vimXX/macros (XX being the version number). Assuming that file location, a function lessc (bash, zsh, ksh users)

        lessc () { /usr/share/vim/vimXX/macros/less.sh "$@"}

is defined and lessc filename is used to view the colorful file contents. The same can be achieved using less and vimcolor, but that is much slower.

5.1.2 List of supported languages

To see which languages are supported the list can be printed using the following colorizer commands:

bat --list-languages
batcat --list-languages
pygmentize -L lexers
source-highlight --lang-list
code2color -h
vimcolor -L (both for vimcolor and nvimpager)

5.2 Colored Directory listing

Depending on the operating system ls is called with appropriate options to produce colored output.

5.3 Colored listing of tar file contents

If the executable archive_color is installed, then the listing of tar file contents is colored in a similar fashion as directory contents.

6. Calling less from standard input

Normally lesspipe.sh is not called when less is used within a pipe, such as

        cat somefile | less

This restriction is removed when the LESSOPEN variable starts with the characters |- or ||-. Then the colon notation for extracting and displaying files in archives does not work. As a way out lesspipe.sh analyses the command line and looks for the last argument given to less. If it starts with a colon, it is interpreted from lesspipe.sh as a continuation of the first parameter. Examples:

        cat some_c_file | less - :c          # equivalent to less some_c_file:c
        cat archive | less - :contained_file # extracts a file from the archive

7. Displaying files with special characters in the file name

Shell meta characters in file names: space (frequently used in windows file names),

the characters | & ; ( ) ` < > " ' # ~ = $ * ? [ ] or \

must be escaped by a \ when used in the shell, e.g. less a\ b.tar.gz:a\\"b will display the file a"b contained in the gzipped tar archive a b.tar.gz.

8. Tab completion for zsh and bash

An existing zsh completion script has been enhanced to provide tab completion within archives, similar to what is possible with the tar command completion. A bash completion script has been modeled loosely after the zsh completion.

In both shells it is now possible to complete contents of archive format files such as tar, zip, rpm, deb files etc. This works as well in compressed files (e.g. tar.gz) and in chained archives, e.g.in source rpm files containing tar.gz files.

To make it work, the script lesscomplete has to be executable and must be found in one of the directories listed in the $PATH environment variable. For zsh the file _less has to be stored in one of the directories listed in $fpath or the directory containing _less has to be added to $fpath, e.g. by:

        fpath=(~/zsh_functions $fpath)

In bash, the function less_completion has to be added to the shell environment by sourcing the script (e.g. from .bashrc using the correct location):

        source ~/bash_functions/less_completion

The completion mechanism is triggered after entering a colon or an equal sign as for example in

        less archive_file:<TAB>                   # and then
        less archive_file:partial_result<TAB>
        less archive_file:contained_archive:<TAB> # etc.

9. 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 the environment variable PATH). That program 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.

10. Debugging

If the script does not work as expected for a given file contents, one could try to output the commands executed by lesspipe.sh. That is achieved by

        bash -x lesspipe.sh file_name > /dev/null # or zsh -x

It is also possible setting temporarily the LESSOPEN variable to e.g.

        LESSOPEN='|bash -x /usr/local/bin/lesspipe.sh %s'

and then use less with the file to be displayed. The normal output goes to STDOUT and the commands executed to STDERR.

11. (Old) documentation about lesspipe

In English

In German:

12. External links

(last checked: Oct 20 2024):

12.1 URLs to some utilities (with last known release)

12.2 References

13. Contributors

The script lesspipe.sh is constantly enhanced by suggestions from users and reporting bugs or deficiencies. Thanks to (in alphabetical order): (contributors after Sep 2015 see github history)

Marc Abramowitz, James Ahlborn, Sören Andersen, Andrew Barnert, Peter D. Barnes, Jr., Eduard Bloch, Mathieu Bouillaguet, Florian Cramer, Philippe Defert, Antonio Diaz Diaz, Bastian Fuchs, Matt Ghali, Carl Greco, Stephan Hegel, Michel Hermier, Tobias Hoffmann, Christian Höltje, Jürgen Kahnert, Sebastian Kayser, Ben Kibbey, Peter Kostka, Heinrich Kuettler, Antony Lee, Vincent Lefèvre, David Leverton, Jay Levitt, Vladimir Linek, Oliver Mangold, Istvan Marko, Markus Meyer, Remi Mommsen, Derek B. Noonburg, Martin Otte, Jim Pryor, Slaven Rezic, Daniel Risacher, Jens Schleusener, Ken Teague, Matt Thompson, Paul Townsend, Petr Uzel, Chelban Vasile, Götz Waschk, Michael Wiedmann, Dale Wijnand, Peter Wu.

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lesspipe - display more with less

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