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Date:      Sun, 20 Sep 2020 19:11:08 +0200
From:      Polytropon <freebsd@edvax.de>
To:        FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   Error message output
Message-ID:  <20200920191108.22864e5c.freebsd@edvax.de>

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I have a general question. Is it still considered useful to
output error messages of a script to standard error?

Example:

	if [ something not okay ]; then
		echo "the error message" > /dev/stderr
		exit 1
	fi

While progress messages will per default go to standard output,
error messages should be printed to standard error. The reason:
If a program is silenced to > /dev/null, error messages will
still be visible (no "silent failing"); if a user wants to
explicitely mute all messages, > /dev/null 2>&1 has to be
specified for the redirection. The judgement if a message is
a regular progress message, an information about some slightly
problematic case, or a real fatal error depends on the programmer.
For example:

	echo "${FILE] processed, ${RECS} records counted."
	 -> standard output

	echo "${DIR} already checked, skipping."
	 -> standard output (non-fatal error"

	echo "${DEV} is read only, aborting."
	exit 1
	 -> standard error (fatal error)

	echo "Cannot start: Input filename missing."
	usage()
	exit 1
	 -> standard error (fatal error)

At least that's what I've learned centuries ago.

Is that still valid?



-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...



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