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.
eval "$(lessfile)"
or
*.arj
*.tar.bz2
*.bz
*.bz2
*.deb, *.udeb
*.doc
*.gif, *.jpeg, *.jpg, *.pcd, *.png, *.tga, *.tiff, *.tif
*.iso, *.raw, *.bin
*.lha, *.lzh
*.pdf
*.rar, *.r[0-9][0-9]
*.rpm
*.tar.gz, *.tgz, *.tar.z, *.tar.dz
*.gz, *.z, *.dz
*.tar
*.jar, *.war, *.xpi, *.zip
*.zoo
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
Sometimes, less does not display the contents file you want to view but output that is produced by your login scripts (~/.bashrc or ~/.bash_profile). This happens because less uses your current shell to run the lesspipe filter. Bash first looks for the variable $BASH_ENV in the environment expands its value and uses the expanded value as the name of a file to read and execute. If this file produces any output less will display this. A way to solve this problem is to put the following lines on the top of your login script that produces output:
if [ -z "$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.