Wednesday, January 13, 2010

MSDOS batch scripting pains

I am a software developer supporting a production application. We have a java - .net -oracle system. I wanted to write a script that could collect the logs from the different servers and bring it to my desktop each morning. As my desktop has windows xp operating I thought I could just create a batch script as I would have if it were a Unix operating system, but to my dismay I found out that batch scripts in DOS is not near as powerful as the shell scripts in Unix. Following are the lessons that I learnt today.

a. One of the requirements of the script was to use ftp to download files from a unix box. For this it is better to create a separate file that contains the commands that need to be run on the ftp prompt and use the file within the batch script. Let us say I needed to connect to the ftp server, change the directory to mydirectory and get all the files having names starting with "myblog".

For this I would create a file called ftptemp.ftp as follows

cd mydirectory
mget *

I would include this file in the batch script. Let us call this file mybatch.bat. In this batch file I first want to change to the directory mylocaldirectory and then download the files to mylocaldirectory. I would create the batch file as follows:

cd c:\mylocaldirectory
ftp -i -s:ftptemp.ftp ftpserver

Option -i turns off interactive prompting for multiple file transfers during the ftp process. This would help when the script has the mget command because it can download multiple files.
Option -s specifies the file that contains the ftp commands.

b. Another requirement was to create a folder that includes the create date and time in the name and then download the files into the newly created folder. In dos batch files, current date is stored in a system variable called date and time is stored in a variable called time. So date could be displayed using the following command:

echo %date%

In DOS batch file processing, a portion of a string can be extracted by using the following command :

%var start,length%
In MS DOS, Jan 13 2010 would be stored as
Wed 01/13/2010
So to extract month portion of the date we would have to use the command %date 4,2%.

The following code can be used to create a folder containing current date and time :
set a=%date:~4,2%%date:~7,2%%date:~10,4%%time:~0,2%%time:~3,2%%time:~6,2%%time:~9,2%md %a% cd %a%
md %a%
cd %a%

c. MSDOS batch scripts do not support arrays. There is a convoluted way of simulating arrays that I didn't want to use. So instead of using batch files I used wscript. So to create a string with yesterday's date in the format ddMonyyyy following code could be used:
dtmYesterday = Date() - 1day1 =CStr(DatePart("d",dtmYesterday))
if len(day1)=1 then set day1="0"&day1 end if
WScript.StdOut.Write (day1+Mid(MonthName(DatePart"m",dtmYesterday)),1,3)+year1)

This code above will throw an error "invalid handle" , if the vbscript is execute directly at the command prompt :

The code would work if the above script is called using cscript.
c:\>cscript vbscriptname.vbs

In conclusion if I have to write the script again, I would use vbscript instead of msdos batch script.