Run ls after cd automatically

April 10, 2015

Tired of running ls after cding into a directory?

@drusepth posted to IRC:

<dru> cd() {
<dru>   echo && builtin cd "$@" && ls -F;
<dru> }
<dru> favorite alias of all time
<dru> (just inconvenient in huge dirs)

Which inspired me to build this monstrosity:

# make cd perform ls, with truncation for long output
cd() { builtin cd "$@" && _truncated_ls }
popd() { builtin popd "$@" && _truncated_ls }
pushd() { builtin pushd "$@" && _truncated_ls }

# try to use gnu's version of ls, needed for --group-directories-first
# on OS X, you'll need to run `brew install coreutils`
if hash gls >/dev/null 2>&1; then
    # gls maps to gnu coreutil's ls on OS X
    _GLS_COMMAND=gls
else
    _GLS_COMMAND=ls
fi

# a pretty ls truncated to at most N lines; helper function for cd, popd, pushd
_truncated_ls() {
    local LS_LINES=8 # use no more than N lines for ls output
    local RESERVED_LINES=5 # reserve N lines of the term, for short windows
    # eg. if a window is only 8 lines high, we want to avoid filling up the
    # whole screen, so instead only 3 lines would be consumed.

    # if using all N lines makes us go over the reserved number of lines
    if [[ $(($LINES - $RESERVED_LINES)) -lt $LS_LINES ]]; then
        local LS_LINES=$(($LINES - $RESERVED_LINES))
    fi

    # compute and store the result of ls
    local RAW_LS_OUT="$(command $_GLS_COMMAND --group-directories-first \
                                              --format=across \
                                              --color=always \
                                              --width=$COLUMNS)"
    local RAW_LS_LINES="$(command wc -l <<< "$RAW_LS_OUT")"

    if [[ $RAW_LS_LINES -gt $LS_LINES ]]; then
        command head -n $(($LS_LINES - 1)) <<< "$RAW_LS_OUT"
        _right_align "... $(($RAW_LS_LINES - $LS_LINES + 1)) lines hidden"
    else
        builtin echo -E "$RAW_LS_OUT"
    fi
}

# right align text and echo it; helper function for _truncated_ls
_right_align() {
    local PADDING=$(($COLUMNS - ${#1}))
    [[ $PADDING -gt 0 ]] && builtin printf "%${PADDING}s"
    builtin echo "$1"
}

For more stuff like this, check out my dotfiles repository.

Updates

In reverse-chronological order.

• Simplified the code by using more zsh/bash built-in features. Relevant commit.

  • Fixed off-by-one issue with _right_align, causing a remaining space at the right-most side.
  • Avoid wc -m by using ${#var} syntax
  • Avoid the loop in _right_align by using printf
  • Use herestrings to avoid calls to echo -E
  • There shouldn’t ever be more than 3 forks caused by running cd now.

• @thomdixon pointed out that OS X’s wc doesn’t support the long-form argument --chars, and that OS X’s ls doesn’t support --group-directories-first. I’ve changed wc to use the short form variant of --chars, -m, and (as a compromise) I now look for gls in the PATH, which can be installed on OS X with brew install coreutils. Relevant commit.

• @thomdixon pointed out that OS X’s wc -l adds spaces before the number. This causes zsh to attempt to treat the number as a command. I’ve added quotes at Thom’s suggestion.