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Accepted
Robert
Asked: 2013-07-27 09:17:18 +0800 CST

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

  • 772

I'm making a backup script for ldap. I want the errors to go to a file in /var/log and the output to go to another file in the backup folder. Currently I'm redirecting to a temp file and then sending the temp file to the log. I'd rather do this as a 1 liner though...

/usr/bin/ldapsearch -x -LLL -b "dc=contoso,dc=com" "(objectclass=*)" -h ldap.server -v 2>>/tmp/ldaptmp.err |
  gzip -c > /mnt/backups/ldap/`date +\%Y\%m\%d`.ldif.gz || 
  logger -t ldapbackup -p local6.err error exit $?

cat /tmp/ldaptmp.err | grep -v "ldap_initialize( ldap://ldap.server )" | 
  grep -v "filter: (objectclass=\*)" |
  grep -v "requesting: All userApplication attributes" >$ERR_LOG
rm -f /tmp/ldaptmp.err

Any ideas on how to redirect stderr and stdout to different pipes to condense this command into 1 line? Or is there a better way?

linux

3 Answers

  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" \
  )
    • 26
  2. Best Answer

    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

    • 11

  3. 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'
    • 2