implementing parallel execution of commands using 'xargs -P' in a shell script
I'm having trouble with executing commands in parallel using `xargs -P` in my shell script. My intention is to process a list of files concurrently, but I'm working with unexpected behavior. The command I'm using looks like this: ```bash cat file_list.txt | xargs -P 4 -I {} sh -c 'echo Processing {}; sleep 2;' ``` While I expect this to process four files simultaneously, it seems to run the commands sequentially instead. I've tried various combinations of `-n` and `-P` options, but the behavior remains the same. I've also checked the contents of `file_list.txt`, which contains valid filenames. The output I see is: ``` Processing file1.txt Processing file2.txt Processing file3.txt Processing file4.txt ``` It takes about 8 seconds for all files to complete, which indicates that they're not actually being processed in parallel. Additionally, when I simplify the command to just use `echo` instead of a shell command, it works as expected and runs concurrently: ```bash cat file_list.txt | xargs -P 4 echo ``` I'm running this on Ubuntu 20.04 with GNU coreutils version 8.30. Any insights on why the commands are not being executed concurrently as intended would be greatly appreciated! Any examples would be super helpful. This issue appeared after updating to Bash 3.9. Cheers for any assistance!