切换到最新或最旧的目录-csh惯用语在bash中不起作用

Question

Please let me know why the following command works in csh mode and not in bash.

Bash:

~ $ cd `ls -ltr | grep ^d | tail -1 | awk '{print $9}'`
bash: cd: synopsys_cache_L-2016.03-SP5: No such file or directory
~ $ pwd
/home/mkumar

after changing to csh:

~ $ csh
CSH > cd `ls -ltr | grep ^d | tail -1 | awk '{print $9}'`
CSH > pwd
/home/mkumar/synopsys_cache_L-2016.03-SP5

Answer 1

Code that relies on parsing ls is innately bug-prone . Don't do it.

The below gets a little fancy, reusing the same code to build both cd_newest and cd_oldest functions:

cd_by_test() {
  local test=$1 dir best_dir=
  shift
  (( "$#" == 0 )) && set -- */
  for dir; do dir=${dir%/}
    [[ -d "$dir" ]] || continue
    [[ $best_dir ]] || best_dir=$dir
    [ "$dir" "$test" "$best_dir" ] && best_dir=$dir
  done
  if [[ $best_dir ]]; then
    cd "$best_dir"
  else
    echo "No directory found" >&2
  fi
}

cd_newest() { cd_by_test -nt "$@"; }
cd_oldest() { cd_by_test -ot "$@"; }

Here, we're setting the operator to use two compare two files by assigning it to the variable $test within the cd_by_test function, and then using [ "$dir" "$test" "$best_dir" ] to apply that operator.

---

In the recently-amended version, we can also pick between a specific subset of directories:

cd_newest *-test.d/

...will cd to the newest *-test.d directory.

Answer 2

Unsolicited plug for zsh (as justification, I'd suggest considering zsh if you are just interested in moving to a shell other than csh ).

% cd *(/om[1])
% pwd
/home/mkumar/synopsys_cache_L-2016.03-SP5

The parentheses following * contain various glob qualifiers :

• / limits the match to directories
• om sorts the expansion by modification time
• [1] selects only the first match