How to add timestamp to STDERR redirection

Question

In bash/ksh can we add timestamp to STDERR redirection?

E.g. myscript.sh 2> error.log

I want to get a timestamp written on the log too.

Answer 1

Rather than writing a script to pipe to, I prefer to write the logger as a function inside the script, and then send the entirety of the process into it with brackets, like so:

 # Vars    
 logfile=/path/to/scriptoutput.log

 # Defined functions
 teelogger(){
   log=$1
   while read line ; do
     print "$(date +"%x %T") :: $line" | tee -a $log
   done
 }


# Start process
{

echo 'well'
sleep 3
echo 'hi'
sleep 3
echo 'there'
sleep 3
echo 'sailor'

}  |  teelogger $logfile

Answer 2

I was too lazy for all current solutions... So I figured out new one (works for stdout could be adjusted for stderr as well):

echo "output" | xargs -L1 -I{} bash -c "echo \$(date +'%x %T') '{}'" | tee error.log

would save to file and print something like that: 11/3/16 16:07:52 output

Details:

-L1 means "for each new line"

-I{} means "replace {} by input"

bash -c is used to update $(date) each time for new call

%x %T formats timestamp to minimal form.

It should work like a charm if stdout and stderr doesn't have quotes (" or `). If it has (or could have) it's better to use:

echo "output" | awk '{cmd="(date +'%H:%M:%S')"; cmd | getline d; print d,$0; close(cmd)} | tee error.log'

(Took from my answer in another topic: https://stackoverflow.com/a/41138870/868947)

Answer 3

The program ts from the moreutils package pipes standard input to standard output, and prefixes each line with a timestamp.

To prefix stdout lines: command | ts
To prefix both stdout and stderr: command 2>&1 | ts

Answer 4

Thought I would add my 2 cents worth..

#!/bin/sh

timestamp(){
  name=$(printf "$1%*s" `expr 15 - ${#1}`)
  awk "{ print strftime(\"%b %d %H:%M:%S\"), \"- $name -\", $$, \"- INFO -\", \$0; fflush() }";
}

echo "hi" | timestamp "process name" >> /tmp/proccess.log

printf "$1%*s" `expr 15 - ${#1}`
Spaces the name out so it looks nice, where 15 is the max space issued, increase if desired

outputs >> Date - Process name - Process ID - INFO - Message

Jun 27 13:57:20 - process name     - 18866 - INFO - hi

Answer 5

Here's a version that uses a while read loop like pax's, but doesn't require extra file descriptors or a separate script (although you could use one). It uses process substitution:

myscript.sh 2> >( while read line; do echo "$(date): ${line}"; done > error.log )

Using pax's predate.sh:

myscript.sh 2> >( predate.sh > error.log )

Answer 6

How about timestamping the remaining output, redirecting all to stdout?

This answer combines some techniques from above, as well as from unix stackexchange here and here. bash >= 4.2 is assumed, but other advanced shells may work. For < 4.2, replace printf with a (slower) call to date.

: ${TIMESTAMP_FORMAT:="%F %T"} # override via environment
_loglines() { 
    while IFS= read -r _line ; do 
      printf "%(${TIMESTAMP_FORMAT})T#%s\n" '-1' "$_line";
    done;
}
exec 7<&2 6<&1
exec &> >( _loglines )
# Logit

To restore stdout/stderr:

exec 1>&6 2>&7

You can then use tee to send the timestamps to stdout and a logfile.

_tmpfile=$(mktemp)
exec &> >( _loglines | tee $_tmpfile )

Not a bad idea to have cleanup code if the process exited without error:

trap "_cleanup \$?" 0 SIGHUP SIGINT SIGABRT SIGBUS SIGQUIT SIGTRAP SIGUSR1 SIGUSR2 SIGTERM
_cleanup() { 
    exec >&6 2>&7
    [[ "$1" != 0 ]] && cat "$_logtemp"
    rm -f "$_logtemp"
    exit "${1:-0}"
}