gistfile1.txt

$ l                 # => ls
$ l /dir            # => ls /dir
$ l file.txt        # => less file.txt
$ l file.gz         # => less with auto-decompress (bzip too)
$ l file.png        # => quicklook file.png
$ l file1 file2...  # => ls file1 file2...

ls-or-view.sh

function l {
  if [[ $# -eq 1 && -f "$1" ]]; then
    pager "$1"
  else
    ls -CFL $*
  fi
}

function pager {
  case "$1" in
    *gz)
      LESSOPEN='|gzip -cdfq -- %s' "$PAGER" "$1"
      ;;
    *bz|*bz2)
      LESSOPEN='|bzip2 -cdfq -- %s' "$PAGER" "$1"
      ;;
    *pdf|*png|*jpg)
      ql "$1"
      ;;
    *)
      "$PAGER" "$1"
      ;;
  esac
}

function ql {
  # Open QuickLook on file (OSX)
  qlmanage -p $*
}