How do I use find command with pipe in bash? - bash

Question

The directory structure looks like
home
--dir1_foo
----subdirectory.....
--dir2_foo
--dir3_foo
--dir4_bar
--dir5_bar
I'm trying to use 'find' command to get directories containing specific strings first, (in this case 'foo'), then use 'find' command again to retrieve some directories matching conditions.
So, I first tried
#!/bin/bash
for dir in `find ./ -type d -name "*foo*" `;
do
for subdir in `find $dir -mindepth 2 -type d `;
do
[Do some jobs]
done
done
, and this script works fine.
Then I thought that using only one loop with pipe like below would also work, but this does not work
#!/bin/bash
for dir in `find ./ -type d -name "*foo*" | find -mindepth 2 -type d `;
do
[Do some jobs]
done
and actually this script works the same as
for dir in `find -mindepth 2 -type d`;
do
[Do some jobs]
done
, which means that the first find command is ignored..
What is the problem?

Answer 1

What your script is doing is not a good practice and has lot of potential pitfalls. See BashFAQ- Why you don't read lines with "for" to understand why.
You can use xargs with -0 to read null delimited files and use the another find command without needing to use the for-loop
find ./ -type d -name "*foo*" -print0 | xargs -0 -I{.} find {.} -mindepth 2 -type d
The string following -I in xargs acts like a placeholder for the input received from the previous pipeline and passes it to the next command. The -print0 option is GNU specific which is a safe option to hande filenames/directory names containing spaces or any other shell meta-characters.
So with the above command in-place, if you are interested in doing some action over the output from 2nd command, do a process-substitution syntax with the while command,
while IFS= read -r -d '' f; do
echo "$f"
# Your other actions can be done on "$f" here
done < <(find ./ -type d -name "*foo*" -print0 | xargs -0 -I{.} find {.} -mindepth 2 -type d -print0)
As far the reason why your pipelines using find won't work is that you are not reading the previous find command's output. You needed either xargs or -execdir while the latter is not an option I would recommend.