Bash – How to stop redirection in bash

bashio-redirectionshell

I use :

exec >script.log 2>&1

in my script to redirect all output to a file. At the end of the script I would like to print a message to the screen. How do I stop the redirection?

Best Answer

You can call exec again to restore the original descriptors. You'll need to have saved them somewhere.

exec 3>&1 4>&2 1>script.log 2>&1
… logged portion …
exec 1>&3 2>&4
echo >&2 "Done"

Inside the logged portion, you can use the original descriptors for one command by redirecting to the extra descriptors.

echo "30 seconds remaining" >&3

Alternatively, you can put the logged portion of your script inside a compound command and redirect that compound command. This doesn't work if you want to use the original descriptors in a trap somewhere within that redirected part.

{
… logged portion …
} >script.log 2>&1
echo >&2 "Done"

Related Solutions

Bash – Use a Variable to Store stderr|stdout Redirection

Another solution could be the following:

#!/bin/bash

verbose=0

exec 3>&1
exec 4>&2

if ((verbose)); then
  echo "verbose=1"
else
  echo "verbose=0"
  exec 1>/dev/null
  exec 2>/dev/null
fi

echo "this should be seen if verbose"
echo "this should always be seen" 1>&3 2>&4

Then add 1>&3 2>&4 only to commands of which you want to see the output.

Linux Bash – How to Change Output Redirection of a Running Process

You can do it using reredirect (https://github.com/jerome-pouiller/reredirect/).

reredirect -m /dev/null <PID>

You can restore initial output of your process later using something like:

reredirect -N -O <M> -E <N> <PID>

(<M> and <N> are provided by previous launch of reredirect).

reredirect README also explains how to redirect to another command or to redirect only stdout or stderr.

Best Answer

Related Solutions

Bash – Use a Variable to Store stderr|stdout Redirection

Linux Bash – How to Change Output Redirection of a Running Process

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