Append text to stderr redirects in bash

Question

Right now I\'m using exec to redirect stderr to an error log with

exec 2>> ${errorLog}

The only downside is that I have to start each

Answer 1

This example redirects stdout and stderr without loosing the original stdout and stderr. Also errors in the stdout handler are logged to the stderr handler. The file descriptors are saved in variables and closed in the child processes. Bash takes care, that no collisions occur.

#! /bin/bash

stamp ()
{
  local LINE
  while IFS='' read -r LINE; do
    echo "$(date '+%Y-%m-%d %H:%M:%S,%N %z') $$ $LINE"
  done
}

exec {STDOUT}>&1
exec {STDERR}>&2
exec 2> >(exec {STDOUT}>&-; exec {STDERR}>&-; exec &>> stderr.log; stamp)
exec > >(exec {STDOUT}>&-; exec {STDERR}>&-; exec >> stdout.log; stamp)

for n in $(seq 3); do
  echo loop $n >&$STDOUT
  echo o$n
  echo e$n >&2
done

This requires a current Bash version but thanks to Shellshock one can rely on this nowadays.