Appending output of a Batch file To log file - batch-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.

Answer 1

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

Answer 2

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:
timeout command 1
timeout command 2
Example (1 second):
TIMEOUT /T 1000 /NOBREAK
Sleep:
sleep command (if sleep.exe is installed)
Example (1 second):
sleep -m 1000
Alternative methods:
Sleeping in a batch file
batch script, put to sleep until certain time
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

Answer 3

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.

Answer 4

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