Backlinks

Bash Script Debug Syslog

(modified )2 min read

This little recipe builds on BashScriptSyslog by adding additional (optional) debug logging to a seperate log file as specified by the $DEBUG_LOGFILE variable.

The log_debug() function will allow you to log messages to debug log file that do not go to the console or syslog.

#!/bin/bash
 
PROG="${0##*/}"
DEBUG_LOGFILE="/tmp/debug.log"
 
function prepend_timestamp() {
    while read line ; do
        echo "$(date +'%d-%m-%y %X') $line"
    done
}
 
function log_debug() {
    echo "$PROG[$$] $*" | prepend_timestamp >> "$DEBUG_LOGFILE"
}
 
if [[ -n "$DEBUG_LOGFILE" ]] ; then
    exec > >(2>&-; \
          logger -s -t "$PROG[$$]" -p user.info 2>&1 \
        | prepend_timestamp | tee -a "$DEBUG_LOGFILE"
      ) 2> >( \
          logger -s -t "$PROG[$$]" -p user.error 2>&1 \
        | prepend_timestamp | tee -a "$DEBUG_LOGFILE" 1>&2
      )
else
    exec > >(2>&-;logger -s -t "$PROG[$$]" -p user.info 2>&1) \
        2> >(logger -s -t "$PROG[$$]" -p user.error)
fi
 
echo "This message went to STDOUT and to syslog FACILITY_USER.LOG_INFO."
ls /tmp
 
log_debug "This message only went to the $DEBUG_LOGFILE log file " \
          "(not to the console or to syslog)."
 
echo "This message went to STDERR and to syslog FACILITY_USER.LOG_ERR."
 >&2
ls /path/does/not/exist

Example Output

Notice that the message 14-03-15 20:05:36 bar.sh[15949] This message only went to the /tmp/debug.log log file (not to the console or to syslog). only appears in the debug log file /tmp/debug.log, and not the console (or syslog; not shown in this example output).

nicolaw@tyrion:~ $ ./bar.sh
14-03-15 20:05:36 bar.sh[15949]: This message went to STDOUT and to syslog FACILITY_USER.LOG_INFO.
14-03-15 20:05:36 bar.sh[15949]: apt-listchanges-tmpoR6QUz
14-03-15 20:05:36 bar.sh[15949]: ls: cannot access /path/does/not/exist: No such file or directory
14-03-15 20:05:36 bar.sh[15949]: debug.log
14-03-15 20:05:36 bar.sh[15949]: ssh-csED0GPnN1
14-03-15 20:05:36 bar.sh[15949]: ssh-rkVTz1ylScj2
14-03-15 20:05:36 bar.sh[15949]: This message went to STDERR and to syslog FACILITY_USER.LOG_ERR.
nicolaw@tyrion:~ $ cat /tmp/debug.log
14-03-15 20:05:36 bar.sh[15949]: This message went to STDOUT and to syslog FACILITY_USER.LOG_INFO.
14-03-15 20:05:36 bar.sh[15949] This message only went to the /tmp/debug.log log file  (not to the console or to syslog).
14-03-15 20:05:36 bar.sh[15949]: ls: cannot access /path/does/not/exist: No such file or directory
14-03-15 20:05:36 bar.sh[15949]: debug.log
14-03-15 20:05:36 bar.sh[15949]: ssh-csED0GPnN1
14-03-15 20:05:36 bar.sh[15949]: ssh-rkVTz1ylScj2
14-03-15 20:05:36 bar.sh[15949]: This message went to STDERR and to syslog FACILITY_USER.LOG_ERR.
nicolaw@tyrion:~ $

~nicolaw

Übergeek & CatLoaf Facilitator