Appending output of a Batch file To log file

Question

I have a batch file which calls a java program.

The output is redirected to a log file in the same directory. However the log file is replaced everytime the batch file is run...

I would like to keep the old outputs in the log file and always append the new output to the log file.

How do you redirect output ALSO to console as well as the log file? — djangofan, Sep 20 '12 at 17:32

score 118 · Accepted Answer · edited Aug 23 '17 at 23:29

118

Instead of using ">" to redirect like this:

java Foo > log

use ">>" to append normal "stdout" output to a new or existing file:

java Foo >> log

However, if you also want to capture "stderr" errors (such as why the Java program couldn't be started), you should also use the "2>&1" tag which redirects "stderr" (the "2") to "stdout" (the "1"). For example:

java Foo >> log 2>&1

edited Aug 23 '17 at 23:29

Dalek Control

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answered Dec 16 '10 at 07:04

Jon Skeet

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Thanks, ">>" worked.....also can you please tell me what lines should i add to my batch file which will make it execute after every 30mins.....along with the Timestamp! – Monojeet Nayak Dec 16 '10 at 07:13
1

@Monojeet: You probably shouldn't do that in your batch file - instead, use Task Scheduler. – Jon Skeet Dec 16 '10 at 07:27
Actually this thing is going to be deployed accross many servers, so not possible to configure task scheduler on every server, a script will be handy! – Monojeet Nayak Dec 16 '10 at 07:35
3

@Monojeet: Well you're basically talking about writing your own scheduler as a script... which doesn't sound like a good idea to me. I'm sure it's possible to remotely configure scheduled tasks, and that would be a better way to go, IMO. If you *really* want to avoid that, I'd put the scheduling in a "proper" program (whether that's Java, a C# wrapper or whatever) rather than trying to do it in a batch file. – Jon Skeet Dec 16 '10 at 07:39
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@Monojeet: You could always make your batch file *invoke* the Windows Task Scheduler, of course, using "at". – Jon Skeet Dec 16 '10 at 07:39
"javaprog %1 %2 >>test.log".....how can i add a timestamp(date and time) to the log file... – Monojeet Nayak Dec 16 '10 at 07:44
@Monojeet: Well, you could run "date /t >> test.log" and "time /t >> test.log" beforehand, assuming you can't change the Java code. – Jon Skeet Dec 16 '10 at 07:49
@John:- yeah , i shud have easily done that if i cud change my code..i have already written the code and checked in :) ...basically its a monitoring java prog which returns certain error codes for a infrastructure...i need to call this java prog at certain intervals( 3mins) so that the monitoring team can pick the error codes and send notifications...Simple!! I have done this thing in Unix...just used the sleep command in the wrapper script....but dont know how do i do that in windows! – Monojeet Nayak Dec 16 '10 at 07:55
@Monojeet: Just because you've checked in the code doesn't mean you can't change it any further... I'd hope, anyway. Otherwise it had better be *perfect* to start with... On Unix I'd use cron rather than sleeping, for a monitoring program. – Jon Skeet Dec 16 '10 at 08:00
@John:- ok , will change the code, was just trying to learn it through the batch file....Thanks a lot for you reply....i saw your profile...it was an honor speaking to you...cheers! – Monojeet Nayak Dec 16 '10 at 08:47

score 4 · Answer 2 · edited May 23 '17 at 12:17

This is not an answer to your original question: "Appending output of a Batch file To log file?"

For reference, it's an answer to your followup question: "What lines should i add to my batch file which will make it execute after every 30mins?"

(But I would take Jon Skeet's advice: "You probably shouldn't do that in your batch file - instead, use Task Scheduler.")

Timeout:

Example (1 second):

TIMEOUT /T 1000 /NOBREAK

Sleep:

sleep command (if sleep.exe is installed)

Example (1 second):

sleep -m 1000

Alternative methods:

Here's an answer to your 2nd followup question: "Along with the Timestamp?"

Create a date and time stamp in your batch files

Example:

echo *** Date: %DATE:/=-% and Time:%TIME::=-% *** >> output.log

score 0 · Answer 3 · answered Feb 14 '13 at 17:00

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Use log4j in your java program instead. Then you can output to multiple media, create rolling logs, etc. and include timestamps, class names and line numbers.

answered Feb 14 '13 at 17:00

Jon Mitchell

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score 0 · Answer 4 · answered Mar 12 '20 at 03:52

It's also possible to use java Foo | tee -a some.log. it just prints to stdout as well. Like:

user at Computer in ~
$ echo "hi" | tee -a foo.txt
hi

user at Computer in ~
$ echo "hello" | tee -a foo.txt
hello

user at Computer in ~
$ cat foo.txt
hi
hello

Appending output of a Batch file To log file

4 Answers4

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