initial commit

log.output.bash

@@ -0,0 +1,73 @@
+#!/bin/bash
+logfile=/tmp/test.log
+
+# Exit-handler to stop all output redirection. 
+on_exit() {
+    local rv="$?"
+
+    # Print message to console and logfile.
+    echo "INFO: Finished at $(date -R), PID $$, exit code $rv" >&2
+
+    # Restore previous standard output and error from FDs 3 and 4;
+    # this will cause the "tee" sub-processes to terminate (EOF); 
+    exec 1>&3 2>&4
+
+    # Reap the sub-processes and evaluate their exit codes.
+
+    wait "$stdout_pid"
+    stdout_rv=$?
+    wait "$stderr_pid"
+    stderr_rv=$?
+
+    # Print final report to console only. 
+
+    if [[ $stdout_rv -ne 0 ]] || [[ $stderr_rv -ne 0 ]]
+    then
+        echo "ERROR: Output redirection to $logfile may be incomplete." >&2
+    fi
+
+    echo "Done (exit code: $rv, see $logfile for details)." >&2
+}
+
+# Initially, no output is logged.
+# Perform some initial greeting / interactions here ...
+
+echo "Note: The following procedure will be logged to $logfile."
+[[ -t 0 ]] && read -rp 'Press ENTER to continue'
+
+# Copy original output FD to FD 3 and original error FD to FD 4.
+exec 3>&1 4>&2
+
+# Redirect standard output and error to sub-processes.
+# Store sub-process PIDs for later reaping.
+
+exec 1> >(tee -ai "$logfile")
+stdout_pid=$!
+
+exec 2> >(tee -ai "$logfile" >&2)
+stderr_pid=$!
+
+# Register exit-handler.
+trap on_exit EXIT
+
+# From here on, all output will be logged to $logfile.
+
+# Print a startup report.
+echo "INFO: Starting at $(date -R), PID $$ ..." >&2 
+
+########################
+# EXAMPLE WORKLOAD BEGIN
+
+# Find and report temporary files older than 15 days.
+# Note: May encounter "permission denied" errors if run as non-root user.
+
+if ! find /tmp -mtime +15 -exec ls -ld "{}" \;
+then
+    echo "ERROR: \"find\" command failed." >&2
+    exit 2
+fi
+
+# EXAMPLE WORKLOAD END
+######################
+
+exit 0