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.

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