List only common parent directories for files - linux

Question

I am searching for one file, say "file1.txt", and output of find command is like below.
/home/nicool/Desktop/file1.txt
/home/nicool/Desktop/dir1/file1.txt
/home/nicool/Desktop/dir1/dir2/file1.txt
In above cases I want only common parent directory, which is "/home/nicool/Desktop" in above case. How it can be achieved using bash? Please help to find general solution for such problem.

Answer 1

This script reads lines and stores the common prefix in each iteration:
# read a line into the variable "prefix", split at slashes
IFS=/ read -a prefix
# while there are more lines, one after another read them into "next",
# also split at slashes
while IFS=/ read -a next; do
new_prefix=()
# for all indexes in prefix
for ((i=0; i < "${#prefix[#]}"; ++i)); do
# if the word in the new line matches the old one
if [[ "${prefix[i]}" == "${next[i]}" ]]; then
# then append to the new prefix
new_prefix+=("${prefix[i]}")
else
# otherwise break out of the loop
break
fi
done
prefix=("${new_prefix[#]}")
done
# join an array
function join {
# copied from: http://stackoverflow.com/a/17841619/416224
local IFS="$1"
shift
echo "$*"
}
# join the common prefix array using slashes
join / "${prefix[#]}"
Example:
$ ./x.sh <<eof
/home/nicool/Desktop1/file1.txt
/home/nicool/Desktop2/dir1/file1.txt
/home/nicool/Desktop3/dir1/dir2/file1.txt
eof
/home/nicool

Answer 2

I don't think there's a bash builtin for this, but you can use this script, and pipe your find into it.
read -r FIRSTLINE
DIR=$(dirname "$FIRSTLINE")
while read -r NEXTLINE; do
until [[ "${NEXTLINE:0:${#DIR}}" = "$DIR" || "$DIR" = "/" ]]; do
DIR=$(dirname "$DIR")
done
done
echo $DIR
For added safety, use -print0 on your find, and adjust your read statements to have -d '\0'. This will work with filenames that have newlines.

Answer 3

lcp() {
local prefix path
read prefix
while read path; do
while ! [[ $path =~ ^"$prefix" ]]; do
[[ $prefix == $(dirname "$prefix") ]] && return 1
prefix=$(dirname "$prefix")
done
done
printf '%s\n' "$prefix"
return 0
}
This finds the longest common prefix of all of the lines of standard input.
$ find / -name file1.txt | lcp
/home/nicool/Desktop