Bash script to remove redundant lines - bash

Question

Good afternoon,
I'm trying to make a bash script that cleans out some data output files. The files look like this:
/path/
/path/to
/path/to/keep
/another/
/another/path/
/another/path/to
/another/path/to/keep
I'd like to end up with this:
/path/to/keep
/another/path/to/keep
I want to cycle through lines of the file, checking the next line to see if it contains the current line, and if so, delete the current line from the file. Here's my code:
for LINE in $(cat bbutters_data2.txt)
do
grep -A1 ${LINE} bbutters_data2.txt
if [ $? -eq 0 ]
then
sed -i '/${LINE}/d' ./bbutters_data2.txt
fi
done

Answer 1

Assuming that your input file is sorted in the way that you have shown:
$ awk 'NR>1 && substr($0,1,length(last))!=last {print last;} {last=$0;} END{print last}' file
/path/to/keep
/another/path/to/keep
How it works
awk reads through the input file line by line. Every time we read a new line, we compare it to the last. If the new line does not contain the last line, then we print the last line. In more detail:
NR>1 && substr($0,1,length(last))!=last {print last;}
If this is not the first line and if the last line, called last, is not contained in the current line, $0, then print the last line.
last=$0
Update the variable last to the current line.
END{print last}
After we finish reading the file, print the last line.

Answer 2

I like the awk solution, but bash itself can handle the task. Note: the solution (both awk and bash), require that the lesser included paths be listed in increasing order. Here is an alternative bash solution (bash only due to the glob match operation):
#!/bin/bash
fn="${1:-/dev/stdin}" ## accept filename or stdin
[ -r "$fn" ] || { ## validate file is readable
printf "error: file not found: '%s'\n" "$fn"
exit 1
}
declare -i cnt=0 ## flag for 1st iteration
while read -r line; do ## for each line in file
## if 1st iteration, fill 'last', increment 'cnt', continue
[ $cnt -eq 0 ] && { last="$line"; ((cnt++)); continue; }
## while 'line' is a child of 'last', continue, else print
[[ $line = "${last%/}"/* ]] || printf "%s\n" "$last"
last="$line" ## update last=$line
done <"$fn"
[ ${#line} -eq 0 ] && ## print last line (updated for non POSIX line end)
printf "%s\n" "$last" ||
printf "%s\n" "$line"
exit 0
Output
$ bash path_uniql.sh < dat/incpaths.txt
/path/to/keep
/another/path/to/keep