Bash me with a pipe

I love to use the pipe. It is a simple tool that brings so much power. So this is how you can take things to the next level.

The snippet below shows how to redirect STDOUT to the STDIN of one script and the STDERR to the STDIN of another.

You cannot use a pipe for both because it will only redirect the file descriptor connected at fd1, normally STDOUT unless you change it. When you use a pipe everything to the right becomes a different program, so STDERR needs a different solution.

The solution is to redirect fd2 before you use the pipe on fd1.

$ crontab -l
# This cron entry sends STDERR to MyErrorLogger.sh and STDOUT to MyLogger.sh
* *  *  *  * ./MyScript.sh 2> >(MyErrorLogger.sh) | MyLogger.sh



$ cat MyLogger.sh 
#!/bin/bash
# This takes STDIN and sends it out to a file that has the date in its name
cat - >> mylog_$(date +%F).log 



$ cat MyErrorLogger.sh 
#!/bin/bash
# This takes STDIN and sends it out to a file that has the date in its name
cat - >> myerrors_$(date +%F).log



$ cat MyScript.sh
#!/bin/bash
# This sends sample text to both STDOUT and STDERR
echo "Hello world!" | tee /dev/fd/2