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Hiding the output of a shell command usually involves redirecting stderr and stdout. Is there any builtin facility or command which by default hides the output but on error dumps all the accumulated output? I would like to run this as a wrapper for remote ssh commands. Now I have them using redirection but I don't get a clue as to what made them fail, and they are just too verbose.

EDIT: In the end I created the following template based on the answer by @Belmin which I tweaked a little bit to accumulate all the previous commands from the script, use the current process identifier, automatically remove the log, and add a failure red error message when something goes wrong. In this template the initial silent wrappers will succeed, then fail the third command because the directory already exists:


set -e

trap "/bin/rm -f $SILENT_LOG" EXIT

function report_and_exit {
    cat "${SILENT_LOG}";
    echo "\033[91mError running command.\033[39m"
    exit 1;

function silent {
    $* 2>>"${SILENT_LOG}" >> "${SILENT_LOG}" || report_and_exit;

silent mkdir -v pepe
silent mkdir -v pepe2
silent mkdir -v pepe
silent mkdir -v pepe2
share|improve this question
If you redirect only stdout, stderr will still show up; is this sufficient for you, or do you want to see stdout as well if there's an error? – Kromey Jun 25 '14 at 16:19
I want to see both but only if something goes wrong, otherwise I don't want to see anything. – Grzegorz Adam Hankiewicz Jun 25 '14 at 16:32
What I do is print stdout & stderr to a logfile so it doesn't clutter the screen. I also print stderr to the screen, so if there is and error I can see it. If I need details I can check the logfile, which contains the program output and the program errors in context. This way, I can 'see both but only if something goes wrong'. Does this help? See… – Stefan Lasiewski Jun 25 '14 at 17:26
up vote 2 down vote accepted

I'd setup a bash function like this:

function surpress { /bin/rm --force /tmp/surpress.out 2> /dev/null; $* 2>&1 > /tmp/surpress.out || cat /tmp/surpress.out; /bin/rm /tmp/surpress.out; }

Then, you could just run the command:

surpress foo -a bar
share|improve this answer
Oh, forgot to remove the test echo command. This should work now. – Belmin Fernandez Jun 25 '14 at 17:41

I don't think there is a clean way of doing this, the only thing I can think of is

  • Capture the output of the command.
  • Check the return value of the command and if it failed
    • display the captured output.

Implementing this might though be a interesting project but perhaps beyond Q&A.

share|improve this answer
Should be doable with a function. Hm, let me give it a try. – Belmin Fernandez Jun 25 '14 at 17:43

It should be easy enough to write a script for this purpose.

Something like this completely untested script.

program_we_want_to_capture &2>1 > $OUTPUT
[ $? -ne 0 ]; then
    cat $OUTPUT
    exit 1

On the other hand for commands I run as part of a script I usually want something better than simply print all the output. I often limit what I see to the unknown. Here is a script I adapted from something I read over a decade ago.


the_command 2>&1 | awk '
  # Initialize our error-detection flag.
  ErrorDetected = 0
# Following are regex that will simply skip all lines
# which are good and we never want to see
/ Added UserList source/ || \
/ Added User/ || \
/ init domainlist / || \
/ init iplist / || \
/ init urllist / || \
/ loading dbfile / || \
/^$/ {next} # Uninteresting message.  Skip it.

# Following are lines that we good and we always want to see
/ INFO: ready for requests / \
  print "  " $0 # Expected message we want to see.

# any remaining lines are unexpected, and probably error messages.  These will be printed out and highlighted.
  print "->" $0 # Unexpected message.  Print it

  if (ErrorDetected == 1) {
    print "Unexpected messages (\"->\") detected in execution."
    exit 2
exit $?
share|improve this answer

going short with something like tehcommand &>/tmp/$$ || cat /tmp/$$

depends how much usability/typing you want/need. (e.g. using it as a pipe or passing the command by argument)

@zoredache short script is basically a proto-wrapper for this, which would give more robustness, handle concurrency, etc

share|improve this answer

Try so:

out=`command args...` || echo $out
share|improve this answer
I'd write it as out="$(command args...)" || echo "$out" – kasperd Jun 26 '14 at 13:38

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