Pipe stderr and stdout to different commands (not just to files)

As indicated by this answer at Unix SE:

MyWeirdCommand.sh

#!/bin/bash
echo "1 2   3"
echo "4 5   6" >&2

testRedirection.sh:

#!/bin/bash
(./MyWeirdCommand.sh | cut -f1 >stdout.log) 3>&1 1>&2 2>&3 | cut -f3 >stderr.log

Running yields:

• stderr.log 6

• stdout.log 1

In Bash, you can use process substitution to manage the extra file descriptors for you. You may find this a little neater looking than the file descriptor swap method.

command > >(process_stdout) 2> >(process_stderr)

Your command might look something like this:

/usr/bin/ldapsearch -x -LLL -b "dc=contoso,dc=com" "(objectclass=*)" -h ldap.server -v \
  > >( \
    gzip -c > /mnt/backups/ldap/$(date '+%Y%m%d').ldif.gz || 
    logger -t ldapbackup -p local6.err error exit $?
  ) \
  2> >( \
    grep -Ev "ldap_initialize( ldap://ldap.server )|filter: (objectclass=\*)|requesting: All userApplication attributes" > "$err_log" \
  )

This is how I print stdout and stderr to separate files with timestamps (piping to ts from Debian moreutils package):

(./my_little_script.pl | ts %F\ %T > out.log) 2>&1 | ts > err.log

P.S. if you don't have ts, make your own alias:

alias ts='while IFS= read -r line; do printf "%s %s\n" "$(date +%F\ %T)" "$line"; done'