Custom format for time command - bash

Question

I'd like to use the time command in a bash script to calculate the elapsed time of the script and write that to a log file. I only need the real time, not the user and sys. Also need it in a decent format. e.g 00:00:00:00 (not like the standard output). I appreciate any advice.
The expected format supposed to be 00:00:00.0000 (milliseconds) [hours]:[minutes]:[seconds].[milliseconds]
I've already 3 scripts. I saw an example like this:
{ time { # section code goes here } } 2> timing.log
But I only need the real time, not the user and sys. Also need it in a decent format. e.g 00:00:00:00 (not like the standard output).
In other words, I'd like to know how to turn the time output into something easier to process.

Answer 1

You could use the date command to get the current time before and after performing the work to be timed and calculate the difference like this:
#!/bin/bash
# Get time as a UNIX timestamp (seconds elapsed since Jan 1, 1970 0:00 UTC)
T="$(date +%s)"
# Do some work here
sleep 2
T="$(($(date +%s)-T))"
echo "Time in seconds: ${T}"
printf "Pretty format: %02d:%02d:%02d:%02d\n" "$((T/86400))" "$((T/3600%24))" "$((T/60%60))" "$((T%60))""
Notes:
$((...)) can be used for basic arithmetic in bash – caution: do not put spaces before a minus - as this might be interpreted as a command-line option.
See also: http://tldp.org/LDP/abs/html/arithexp.html
EDIT:
Additionally, you may want to take a look at sed to search and extract substrings from the output generated by time.
EDIT:
Example for timing with milliseconds (actually nanoseconds but truncated to milliseconds here). Your version of date has to support the %N format and bash should support large numbers.
# UNIX timestamp concatenated with nanoseconds
T="$(date +%s%N)"
# Do some work here
sleep 2
# Time interval in nanoseconds
T="$(($(date +%s%N)-T))"
# Seconds
S="$((T/1000000000))"
# Milliseconds
M="$((T/1000000))"
echo "Time in nanoseconds: ${T}"
printf "Pretty format: %02d:%02d:%02d:%02d.%03d\n" "$((S/86400))" "$((S/3600%24))" "$((S/60%60))" "$((S%60))" "${M}"
DISCLAIMER:
My original version said
M="$((T%1000000000/1000000))"
but this was edited out because it apparently did not work for some people whereas the new version reportedly did. I did not approve of this because I think that you have to use the remainder only but was outvoted.
Choose whatever fits you.

Answer 2

To use the Bash builtin time rather than /bin/time you can set this variable:
TIMEFORMAT='%3R'
which will output the real time that looks like this:
5.009
or
65.233
The number specifies the precision and can range from 0 to 3 (the default).
You can use:
TIMEFORMAT='%3lR'
to get output that looks like:
3m10.022s
The l (ell) gives a long format.

Answer 3

From the man page for time:
There may be a shell built-in called time, avoid this by specifying /usr/bin/time
You can provide a format string and one of the format options is elapsed time - e.g. %E
/usr/bin/time -f'%E' $CMD
Example:
$ /usr/bin/time -f'%E' ls /tmp/mako/
res.py res.pyc
0:00.01

Answer 4

Use the bash built-in variable SECONDS. Each time you reference the variable it will return the elapsed time since the script invocation.
Example:
echo "Start $SECONDS"
sleep 10
echo "Middle $SECONDS"
sleep 10
echo "End $SECONDS"
Output:
Start 0
Middle 10
End 20

Answer 5

Not quite sure what you are asking, have you tried:
time yourscript | tail -n1 >log
Edit: ok, so you know how to get the times out and you just want to change the format. It would help if you described what format you want, but here are some things to try:
time -p script
This changes the output to one time per line in seconds with decimals. You only want the real time, not the other two so to get the number of seconds use:
time -p script | tail -n 3 | head -n 1

Answer 6

The accepted answer gives me this output
# bash date.sh
Time in seconds: 51
date.sh: line 12: unexpected EOF while looking for matching `"'
date.sh: line 21: syntax error: unexpected end of file
This is how I solved the issue
#!/bin/bash
date1=$(date --date 'now' +%s) #date since epoch in seconds at the start of script
somecommand
date2=$(date --date 'now' +%s) #date since epoch in seconds at the end of script
difference=$(echo "$((date2-$date1))") # difference between two values
date3=$(echo "scale=2 ; $difference/3600" | bc) # difference/3600 = seconds in hours
echo SCRIPT TOOK $date3 HRS TO COMPLETE # 3rd variable for a pretty output.