LESSOPEN(1) General Commands Manual LESSOPEN(1)
NAME
lessfile, lesspipe - "input preprocessor" for less.
SYNOPSIS
lessfile, lesspipe
DESCRIPTION
This manual page documents briefly the lessfile, and lesspipe commands.
This manual page was written for the Debian GNU/Linux distribution be-
cause the input preprocessor scripts are provided by Debian GNU/Linux
and are not part of the original program.
lessfile and lesspipe are programs that can be used to modify the way
the contents of a file are displayed in less. What this means is that
less can automatically open up tar files, uncompress gzipped files, and
even display something reasonable for graphics files.
lesspipe will toss the contents/info on STDOUT and less will read them
as they come across. This means that you do not have to wait for the
decoding to finish before less shows you the file. This also means that
you will get a 'byte N' instead of an N% as your file position. You can
seek to the end and back to get the N% but that means you have to wait
for the pipe to finish.
lessfile will toss the contents/info on a file which less will then
read. After you are done, lessfile will then delete the file. This
means that the process has to finish before you see it, but you get nice
percentages (N%) up front.
USAGE
Just put one of the following two commands in your login script (e.g.
~/.bash_profile):
eval "$(lessfile)"
or
eval "$(lesspipe)"
FILE TYPE RECOGNITION
File types are recognized by their extensions. This is a list of cur-
rently supported extensions (grouped by the programs that handle them):
*.a
*.arj
*.tar.bz2
*.bz
*.bz2
*.deb, *.udeb, *.ddeb
*.doc
*.egg
*.gif, *.jpeg, *.jpg, *.pcd, *.png, *.tga, *.tiff, *.tif
*.iso, *.raw, *.bin
*.lha, *.lzh
*.tar.lz, *.tlz
*.lz
*.7z
*.pdf
*.rar, *.r[0-9][0-9]
*.rpm
*.tar.gz, *.tgz, *.tar.z, *.tar.dz
*.gz, *.z, *.dz
*.tar
*.tar.xz, *.xz
*.whl
*.jar, *.war, *.xpi, *.zip
*.zoo
*.tar.zst, *.tzst
*.zst
USER DEFINED FILTERS
It is possible to extend and overwrite the default lesspipe and lessfile
input processor if you have specialized requirements. Create an exe-
cutable program with the name .lessfilter and put it into your home di-
rectory. This can be a shell script or a binary program.
It is important that this program returns the correct exit code: return
0 if your filter handles the input, return 1 if the standard
lesspipe/lessfile filter should handle the input.
Here is an example script:
#!/bin/sh
case "$1" in
*.extension)
extension-handler "$1"
;;
*)
# We don't handle this format.
exit 1
esac
# No further processing by lesspipe necessary
exit 0
FILES
~/.lessfilter
Executable file that can do user defined processing. See section
USER DEFINED FILTERS for more information.
BUGS
Sometimes, less does not display the contents file you want to view but
output that is produced by your login scripts (~/.bashrc or ~/.bash_pro-
file). This happens because less uses your current shell to run the
lesspipe filter. Bash first looks for the variable $BASH_ENV in the en-
vironment expands its value and uses the expanded value as the name of
a file to read and execute. If this file produces any output less will
display this. A way to solve this problem is to put the following lines
on the top of your login script that produces output:
if [ -z "$PS1" ]; then
exit
fi
This tests whether the prompt variable $PS1 is set and if it isn't
(which is the case for non-interactive shells) it will exit the script.
SEE ALSO
less(1)
AUTHOR
This manual page was written by Thomas Schoepf <schoepf@debian.org>, for
the Debian GNU/Linux system (but may be used by others). Most of the
text was copied from a description written by Darren Stalder
<torin@daft.com>.
LESSOPEN(1)
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