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Is there any way, in bash, to pipe STDERR through a filter before unifying it with STDOUT? That is, I want
STDOUT ────────────────┐ ├─────> terminal/file/whatever STDERR ── [ filter ] ──┘ rather than
STDOUT ────┐ ├────[ filter ]───> terminal/file/whatever STDERR ────┘ 
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As redirection is a method of capturing a program output and sending it as an input to another command or file. The I/O streams can be redirected by putting the n> operator in use, where n is the file descriptor number. For redirecting stdout, we use “1>” and for stderr, “2>” is added as an operator.
The regular output is sent to Standard Out (STDOUT) and the error messages are sent to Standard Error (STDERR). When you redirect console output using the > symbol, you are only redirecting STDOUT. In order to redirect STDERR, you have to specify 2> for the redirection symbol.
The standard error is calculated by dividing the standard deviation by the sample size's square root. It gives the precision of a sample mean by including the sample-to-sample variability of the sample means.
Here's an example, modeled after how to swap file descriptors in bash . The output of a.out is the following, without the 'STDXXX: ' prefix.
STDERR: stderr output STDOUT: more regular ./a.out 3>&1 1>&2 2>&3 3>&- | sed 's/e/E/g' more regular stdErr output Quoting from the above link:
- First save stdout as &3 (&1 is duped into 3)
- Next send stdout to stderr (&2 is duped into 1)
- Send stderr to &3 (stdout) (&3 is duped into 2)
- close &3 (&- is duped into 3)
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