How do I print all the parent directories in Bash

Question

I have a text file containing some directories.

For example

./dir1/dir2/dir3
./dir4/dir5

And I want to end up with a file text with the list of all the subdirectories :

.
./dir1
./dir1/dir2
./dir1/dir2/dir3
./dir4
./dir4/dir5

I tried this way but it won't work

cat folders_recently_used | xargs -I {} sh -c 'TEST={} ;
     while true; 
     do dirname $TEST; 
          if [ $(dirname $TEST) == '.' ]; 
             then break ; 
             else $TEST = $(dirname $TEST);
          fi  ; done' > folders_to_use

Answer 1

Here's another way using a bash array and no external child processes:

#!/bin/bash

while IFS='/' read -a path
do
    prefix=""
    for ((i=0; i < ${#path[@]}; i++))
    do
        echo "$prefix${path[i]}"
        prefix="$prefix${path[i]}/"
    done
done < folders_recently_used

For the supplied example data, this gives:

.
./dir1
./dir1/dir2
./dir1/dir2/dir3
.
./dir4
./dir4/dir5

The IFS='/' makes the Internal Field Separator the / character so that it splits the string on the /. read -a reads one field into each element of an array, in this case the array is called path.

for ((i=0; i < ${#path[@]}; i++)) iterates through the array indexes (i). ${#path[@]} gives the number of elements in the array, in this case that is the number of directories in the path.

The rest is just string concatenation.

Answer 2

File:

$ cat subdirs
./dir1/dir2/dir3
./dir4/dir5

Script (ugly a bit, but works fine):

#!/bin/bash

while read line
do
    counter=$(echo "${line}" | grep -o '/' | wc -l)
    i=1
    j=$(($i + 1))
    echo "Original string: ${line}"
    echo "Its parent directories:"
    while [ "${counter}" -gt 0 ]
    do
            echo "${line}" | cut -d'/' -f$i-$j
            counter=$(($counter - 1))
            j=$(($j + 1))
    done
    echo "Next one if exists..."
    echo ""
done < subdirs

Output:

Original string: ./dir1/dir2/dir3
Its parent directories:
./dir1
./dir1/dir2
./dir1/dir2/dir3
Next one if exists...

Original string: ./dir4/dir5
Its parent directories:
./dir4
./dir4/dir5
Next one if exists...