How to silence output in a Bash script?
BashBash Problem Overview
I have a program that outputs to stdout and would like to silence that output in a Bash script while piping to a file.
For example, running the program will output:
% myprogram
% WELCOME TO MY PROGRAM
% Done.
I want the following script to not output anything to the terminal:
#!/bin/bash
myprogram > sample.s
Bash Solutions
Solution 1 - Bash
If it outputs to stderr as well you'll want to silence that. You can do that by redirecting file descriptor 2:
# Send stdout to out.log, stderr to err.log
myprogram > out.log 2> err.log
# Send both stdout and stderr to out.log
myprogram &> out.log # New bash syntax
myprogram > out.log 2>&1 # Older sh syntax
# Log output, hide errors.
myprogram > out.log 2> /dev/null
Solution 2 - Bash
Redirect stderr to stdout
This will redirect the stderr (which is descriptor 2) to the file descriptor 1 which is the the stdout.
2>&1
Redirect stdout to File
Now when perform this you are redirecting the stdout to the file sample.s
myprogram > sample.s
Redirect stderr and stdout to File
Combining the two commands will result in redirecting both stderr and stdout to sample.s
myprogram > sample.s 2>&1
Redirect stderr and stdout to /dev/null
Redirect to /dev/null
if you want to completely silent your application.
myprogram >/dev/null 2>&1
Solution 3 - Bash
All output:
scriptname &>/dev/null
Portable:
scriptname >/dev/null 2>&1
Portable:
scriptname >/dev/null 2>/dev/null
For newer bash (no portable):
scriptname &>-
Solution 4 - Bash
If you are still struggling to find an answer, specially if you produced a file for the output, and you prefer a clear alternative:
echo "hi" | grep "use this hack to hide the oputut :) "
Solution 5 - Bash
If you want STDOUT and STDERR both [everything], then the simplest way is:
#!/bin/bash
myprogram >& sample.s
then run it like ./script
, and you will get no output to your terminal. :)
the ">&" means STDERR and STDOUT. the &
also works the same way with a pipe: ./script |& sed
that will send everything to sed
Solution 6 - Bash
Try with:
myprogram &>/dev/null
to get no output
Solution 7 - Bash
Useful variations:
-
Get only the STDERR in a file, while hiding any STDOUT even if the program to hide isn't existing at all. (does not ever hang):
stty -echo && ./programMightNotExist 2> errors.log && stty echo
-
Detach completely and silence everything, even killing the parent script won't abort
./prog
(Does behave just likenohup
):./prog </dev/null >/dev/null 2>&1 &
-
nohup
can be used as well to fully detach, as follow:nohup ./prog &
A log file
nohup.out
will be created aside of the script, usetail -f nohup.out
to read it.
Solution 8 - Bash
Note: This answer is related to the question "How to turn off echo while executing a shell script Linux" which was in turn marked as duplicated to this one.
To actually turn off the echo the command is: > stty -echo
(this is, for instance; when you want to enter a password and you don't want it to be readable. Remember to turn echo on at the end of your script, otherwise the person that runs your script won't see what he/she types in from then on. To turn echo on run: > stty echo