can I get the shell to decide ls or less depending on filetype?

Question

Very often I find myself looking through directories using 'ls', then when I find the file I want, I use 'less' to look at the file.

So for example to find a mysql log file I might type
ls /var

then:
ls /var/log/

and then:
ls /var/log/mysql

and finally:
less /var/log/mysql/mysql.log

(its a bit of a contrived example, but hopefully you know what I am doing)

I find it annoying that I need to decide if the command should be ls or less. Why can't 'less' determine if it has been given a directory and act as 'ls' ?

Is there a command that I can use instead of less that will act as ls or less depending on the file type ? Or is there a common alias that people use ?

Answer 1

Less can determine if it has been given a directory. Set the LESSOPEN environment variable to ~/bin/LESSPIPE and make ~/bin/LESSPIPE a script like the following:

#!/bin/sh
if [ -d "$1" ]; then
  exec /bin/ls -la "$1"
elif [ -f "$1" ]; then
  case "$1" in
    *.tar|ztar) exec tar tvvf "$1" 2>/dev/null;;
    *.tar.[dg]z|*.tar.z|*.tgz) exec gzip -dc "$1" | tar tvvf - 2>/dev/null;;
    *.tar.bz2) exec bzip2 -d <"$1" 2>/dev/null | exec tar tvvf - 2>/dev/null;;
    *.tar.Z|*.taz) exec uncompress -c "$1" | exec tar tvvf - 2>/dev/null;;
    *.zip) exec unzip -l "$1" 2>/dev/null;;
    *.lha) exec lha -v "$1" 2>/dev/null;;
    *.7z) exec 7z l "$1" 2>/dev/null;;
    *.[rs]pm) exec rpm -qilp "$1";;
    *.z|*.[dg]z) exec gzip -dc "$1" 2>/dev/null;;
    *.bz2) exec bzip2 -dc "$1";;
    *.xz) exec xz -dc "$1";;
    *.Z) exec uncompress -c "$1" 2>/dev/null;;
  esac
fi

You'll get a listing for directories and archives.

You can use lesskey instead of the environment variable to set the preprocessor. See the documentation for details.

Answer 2

In bash you could easily create a function to do this:

function less_ls()
{
  # True if file exists and is a regular file.
  if [ -f "${1}" ]
  then
    less "${1}"
  else
    ls "${1}"
  fi
}

Obviously you can rename the function into whatever you want by replacing the less_ls part, if you name it less it will have precedence of the executable less. If you want this to be defined automatically every time you start Bash you could copy paste it into your ~/.bashrc file.