[Linux 常見問題] Bash: How to read one line at a time from output of a command?

Source From Here
Question
I am trying to read the output of a command in bash using a while loop:
- test.sh

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1. #!/bin/bash  
2. while read -r line  
3. do  
4.     echo "$line"  
5. done <<< $(find . -type f)  

The output I got:

# ./test.sh
./DebugPy.py ./DebugPy.pyc ./zombe.py ./test.sh

After this I tried:
- test2.sh

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1. #!/bin/bash  
2. $(find . -type f) |  
3. while read -r line  
4. do  
5.     echo "$line"  
6. done  

but it generated an error "Error: Must provide process id to debug" So, how do I read it line by line because I think currently it is slurping the entire line at once.

How-To
There's a mistake, you need < <(command) not <<<$(command). < <( ) is a Process Substitution, $() is a command substitution and <<< is a here-string. So you can do it this way:
- test3.sh

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1. #!/bin/bash  
2. find . -type f |  
3. while read -r line; do  
4.   echo "$line"  
5. done  

The execution result:

# ./test3.sh
./DebugPy.py
./DebugPy.pyc
./test3.sh
./test2.sh
./zombe.py
./test.sh

Another approach using Process Substitution:
- test4.sh

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1. #!/bin/bash  
2. while read -r line; do  
3.     echo "$line"  
4. done < <(find . -type f)  

Some advantages of process substitution:

* No need to save temporary files.
* Better performance. Reading from another process often faster than writing to disk, then read back in.
* Save time to computation since when it is performed simultaneously with parameter and variable expansion, command substitution, and arithmetic expansion