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See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, stdout and stderr are both printed to your screen:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

To hide stdout, but still print stdout do this:

$ ./stdout-stderr.sh >/dev/null
./stdout-stderr.sh: Printing to stderr

But grep won't operate on stderr! You would expect the following command to suppress lines which contain 'err', but it does not.

$ ./stdout-stderr.sh >/dev/null |grep --invert-match err
./stdout-stderr.sh: Printing to stderr

Here's the solution.

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ ./stdout-stderr.sh 2>&1 >/dev/null | grep err
./stdout-stderr.sh: Printing to stderr

(Note that the above command is different then ./command >/dev/null 2>&1, which is a very common command).

Here's the script used for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0

See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, stdout and stderr are both printed to your screen:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

To hide stdout, but still print stderr do this:

$ ./stdout-stderr.sh >/dev/null
./stdout-stderr.sh: Printing to stderr

But grep won't operate on stderr! You would expect the following command to suppress lines which contain 'err', but it does not.

$ ./stdout-stderr.sh >/dev/null |grep --invert-match err
./stdout-stderr.sh: Printing to stderr

Here's the solution.

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ ./stdout-stderr.sh 2>&1 >/dev/null | grep err
./stdout-stderr.sh: Printing to stderr

(Note that the above command is different then ./command >/dev/null 2>&1, which is a very common command).

Here's the script used for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0

See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, stdout and stderr are both printed to your screen:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

To hide stdout, but still print stdout do this:

$ ./stdout-stderr.sh >/dev/null
./stdout-stderr.sh: Printing to stderr

But grep won't operate on stderr! You would expect the following command to suppress lines which contain 'err', but it does not.

$ ./stdout-stderr.sh >/dev/null |grep --invert-match err
./stdout-stderr.sh: Printing to stderr

Here's the solution.

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ { ./stdout-stderr.sh >/dev/null ; } 2>&1  | grep err
./stdout-stderr.sh: Printing to stderr

Here's the script used for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0

See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, stdout and stderr are both printed to your screen:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

To hide stdout, but still print stdout do this:

$ ./stdout-stderr.sh >/dev/null
./stdout-stderr.sh: Printing to stderr

But grep won't operate on stderr! You would expect the following command to suppress lines which contain 'err', but it does not.

$ ./stdout-stderr.sh >/dev/null |grep --invert-match err
./stdout-stderr.sh: Printing to stderr

Here's the solution.

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ ./stdout-stderr.sh 2>&1 >/dev/null | grep err
./stdout-stderr.sh: Printing to stderr

(Note that the above command is different then ./command >/dev/null 2>&1, which is a very common command).

Here's the script used for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0

See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, output is printed to both stdout and stderr:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

So we hide output to stdout:

$ { ./stdout-stderr.sh >/dev/null ; } 2>&1
./stdout-stderr.sh: Printing to stderr

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ { ./stdout-stderr.sh >/dev/null ; } 2>&1  | grep err
./stdout-stderr.sh: Printing to stderr

Here's the script I use for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0

See below for the script used in these tests.

Grep can only operate on stdin, so therefore you must convert the stderr stream in a form that Grep can parse.

Normally, stdout and stderr are both printed to your screen:

$ ./stdout-stderr.sh
./stdout-stderr.sh: Printing to stdout
./stdout-stderr.sh: Printing to stderr

To hide stdout, but still print stdout do this:

$ ./stdout-stderr.sh >/dev/null
./stdout-stderr.sh: Printing to stderr

But grep won't operate on stderr! You would expect the following command to suppress lines which contain 'err', but it does not.

$ ./stdout-stderr.sh >/dev/null |grep --invert-match err
./stdout-stderr.sh: Printing to stderr

Here's the solution.

The following Bash syntax will hide output to stdout, but will still show stderr. First we pipe stdout to /dev/null, then we convert stderr to stdout, because Unix pipes will only operate on stdout. You can still grep the text.

$ { ./stdout-stderr.sh >/dev/null ; } 2>&1  | grep err
./stdout-stderr.sh: Printing to stderr

Here's the script used for testing. This prints one line to stdout and one line to stderr:

#!/bin/sh

# Print a message to stdout
echo "$0: Printing to stdout"
# Print a message to stderr
echo "$0: Printing to stderr" >&2

exit 0