Assorted Batch Tricks Thu 22-October-1992 ===================== By prof. Timo Salmi Moderating at garbo.uwasa.fi anonymous FTP archives 128.214.87.1 Faculty of Accounting & Industrial Management; University of Vaasa Internet: ts@uwasa.fi Bitnet: salmi@finfun ; SF-65101, Finland .................................................................. 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � This file belongs to TSBAT*.ZIP. Please do not distribute � � this batricks.txt file separately. � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Introduction ============ This file contains assorted batch tricks. Many, but not all, have been used in the TSBAT*.ZIP collection of batches. Likewise, there are some useful further tricks, not documented here, to be found in the TSBAT batches. INDEX ===== 1) Making "@echo off" general 2) Deleting All Files 3) Nested Loops 4) Checking whether a directory exists 5) Checking that a program is available at the current directory or at path 6) Using subroutines in batches 7) Convert a parameter to uppercase 8) Appending a new directory to the path 9) Comparing two files 10) Writing an empty line 11) Customizing the pause message 12) Complicate renaming with for 13) Checking for wildcards 14) Preventing breaking the batch 15) Prevent a break from bypassing your autoexec.bat 16) Getting the extension 17) The quote character % 18) Eliminating auxiliary batches 19) Utilizing the subst command in paths 20) How to run a batch once a week (testing for the weekday) 1. Making "@echo off" general ============================= If you want to turn the echo off, and do not wish to show that line on the screen, you can easily do this by applying @echo off There is a catch, however, because this only works since MsDos version 3.30. So if you want to make it general, put the following line in your autoexec.bat file if you are using MsDos 3.30 or higher set _echo=@ Then use the following format in your batches, which will then work for any MsDos version %_echo%echo off 2. Deleting All Files ===================== One of the most Frequently Asked Questions (FAQs) about batches is how to suppress the "Are you sure (Y/N)?" confirmation requirement for del *.*. Use the following: echo y| del *.* If you wish to suppress the message too, use echo y| del *.* > nul Whether or not it is sensible to suppress the confirmation can be debated, but this is the trick anyway. 3. Nested Loops =============== It is possible to have nested loops of a kind in batch programming. Consider the following two batches, and try it out by calling test.bat. echo off rem TEST.BAT for %%f in (a b c d e f) do %comspec% /c test2 %%f echo off rem TEST2.BAT for %%g in (1 2 3) do echo %1%%g 4. Checking whether a directory exists ====================================== It is sometimes useful to be able to test whether a particular directory exists. The following test is true if the %1 directory does not exist. if not exist %1\nul if not exist %1nul echo Directory %1 does not exist 5. Checking that a program is available at the current directory or at path =========================================================================== When you call a program from a batch, and do not give the explicit path to it, it is advisable to test that the program is available either at the current directory or the default path. set _found= if exist %1 set _found=yes for %%d in (%path%) do if exist %%d\%1 set _found=yes for %%d in (%path%) do if exist %%d%1 set _found=yes if "%_found%"=="yes" goto _continue echo %1 is not at path or the current directory goto _out :_continue echo %1 found at path or in the current directory :_out 6. Using subroutines and recursion in batches ============================================= It is possible to use subroutines within batches. The crucial trick is setting an environment variable (eg _return) to point to a label where to return after the subroutine has been performed. For an example see UNPACK.BAT, and BOOT.BAT, the sections :_common and :_subru. 7. Convert a parameter to uppercase =================================== This example shows how to ensure that the parameter %1 given to the batch is in uppercase. This utilizes the fact that MsDos converts the path to uppercase. The result is stored in upcase_ and then the original path is restored. set tmp_=%path% path=%1 set upcase_=%path% path=%tmp_% 8. Appending a new directory to the path ======================================== This often needed trick is basically very simple. For example to add directory %1 to path use path=%path%;%1 Note that you can only use this trick in a batch. It will not work at the MsDos prompt because the environment variables are expanded (%path%) only within batches. For a full treatment with safeguards against appending non-existing directories, or appending twice, see ADDPATH.BAT. 9. Comparing two files ====================== It is possible in batch programming to test whether or not two files have identical contents. This trick utilizes th external MsDos programs fc.exe and find.exe. (An external MsDos program means, of course, a program that comes with the standard MsDos releases. Most often the MsDos external support files are located in a c:\dos directory.) fc %1 %2 > tmp$$$ type tmp$$$ | find /i "fc: no differences encountered" > diffe$$$ if exist notsame$ del notsame$$$ copy diffe$$$ notsame$ > nul if not exist notsame$ echo Files %1 and %2 are different if exist notsame$ echo Files %1 and %2 are identical if exist tmp$$$ del tmp$$$ if exist notsame$ del notsame$ if exist diffe$$$ del diffe$$$ If you think about, this idea can be used for other useful purposes, too, because it establishes whether a given string is found in a text file. 10. Writing an empty line ========================= This is a simple, but an often needed, useful trick. Just use echo with (for example) a point (.) after it. As you can see, I have utilized this batch feature extensively in my batch collection. echo. 11. Customizing the pause message ================================= You can easily customize the message given by pause by giving your own with echo and directing the pause message to nul. to nul. echo Break to quit, any other key to remove the tmp directory pause > nul 12. Complicate renaming with for ================================ Although this is basically trivial, one does not necessarily come to thing of it. The for statement is quite useful for involved renaming of files. An example delineates. For example I have the following files (Turbo Pascal units for TP 4.0, 5.0, 5.5 and 6.0). Say that I wish to rename them to be version 30 instead of 29. tspa2940.zip tspa2950.zip tspa2955.zip tspa2960.zip The following for-statement does that conveniently. for %f in (40 50 55 60) do ren tspa29%f.zip tspa30%f.zip Naturally, renaming is not the only task that can utilize this trick. I am sure you can readily think of others, like for %d in (a b) do format %d: 13. Checking for wildcards ========================== This example shows how you can test whether a parameter (%1) of a batch contains wildcards. @echo off for %%f in (%1) do if "%%f"=="%1" goto _nowilds echo Parameter %1 contains wildcards (or is missing) :_nowilds 14. Preventing breaking the batch ================================= It is possible to prevent user interrupt of a batch by using the ctty command to reassign the input (and the output) device. Here is an example (an elementary password batch requiring inputting an e). Note the < and > redirections which are needed while the ctty has been assigned to nul. The ask batch enhancer is included in the TSBAT collection. @echo off ctty nul echo Now you cannot break the batch with ^C or ^Break > con :_ask echo Use e to break > con ask /b /d < con if errorlevel==101 if not errorlevel==102 goto _out goto _ask :_out ctty con echo Back to normal. Now you can break the batch with ^C or ^Break. Note that this trick does not prevent you from rebooting with alt-crtl-del while the batch is running. For that you need an external program like noboot.exe from garbo.uwasa.fi:/pc/ts/ tstsr13.zip (os whichever version number is current). 15. Prevent a break from bypassing your autoexec.bat ==================================================== You can actually prevent a quick tapping of the break from bypassing your autoexec.bat by a variation of the trick in the item above. Put for example shell=c:\command.com /p nul in your config.sys. Before you do, make sure to have a floppy to boot from in case something goes wrong. I first saw trick when it was posted in the UseNet comp.os.msdos.programmer newsgroup by Joseph Gil yogi@cs.ubc.ca. This is not, however, quite all there is to it. You should put ctty con as the last line to your autoexec.bat. If you don't, the keyboard will not be responding, and you must boot from the floppy you so sensibly had prepared :-). 16. Getting the extension ========================= It would be quite useful to be able to extract the extension of a given file name into an environment variable. Or to be able just to test whether there is an extension. Here is how to do that. The batch is based on the information in PC-Magazine July 1992, Vol 11, No. 13, page 528. It gives the crucial information that if one precedes the argument of a for loop with a slash (/), then the argument is interpreted in two parts. The first part is the first character of the argument, the second part all the rest. Neat, indeed. The problem with my solution below is that it will not recognize .* or .??? as extensions. But, of course, one can first test for wildcards as shown in a previous item "Checking for wildcards". See e.g. UNPACK.BAT for the utilization of this method. @echo off set exten_=%1 :_next set prev_=%exten_% for %%f in (/%exten_%) do set exten_=%%f if ".%exten_%"=="%prev_%" goto _extfound if not "%exten_%"=="%prev_%" goto _next goto _noext :_extfound echo The filename %1 has an extension %exten_% goto _out :_noext echo The filename %1 has no extension :_out set exten_= set prev_= 17. The quote character % ========================= As we know %1 indicates the first parameter given to a batch. Thus for example echo %1 echoes that parameter. But what if you ant to echo the actual string %1 instead. The % character acts as a quote character. Thus echo %%1 will indeed be a "%1" instead of its usual interpretation. Try the following simple test @echo off if "%1"=="" goto _out echo %1 echo %%1 :_out See the item on "Eliminating auxiliary batches" for utilizing this feature. A good example of utilizing this feature is given by DELPATH.BAT. 18. Eliminating auxiliary batches ================================= Quite a number of batch programming tasks require an auxiliary batch which the primary batch has to call. Many of these cases can be eliminated by making the batch call itself (a kind of recursion). The auxiliary code is put in the batch itself. The trick is best illustrated by looking at the SHOW.BAT, which provides a wild-carded TYPE command, and would normally need an auxiliary file to type each of the individual files. Another example is given by the SAFEDEL.BAT batch. There is also an another trick for a similar purpose. The primary batch creates and auxiliary batch or batches, which it then calls. See DELPATH.BAT for an example of this method. There was an inventive twist of this method in PC-Magazine August 1992, Vol. 11, No. 14, p. 527 for getting the volume label of a disk. Here is my own example using the same techniques. It sets the current directory in an environment variable getdir_. I have utilized this technique in PUSHDIRE.BAT. @echo off echo @echo off> director.bat echo set getdir_=%%2>> director.bat echo echo %%getdir_%%>> director.bat dir | find "Directory"> go.bat call go if exist director.bat del director.bat if exist go.bat del go.bat 19. Utilizing the subst command in paths ======================================== I use the following kind of a simple batch to make some of my directories easy to reach. The way this simple batch is written it avoids unnecessary errors if the substitution already has been made. As a last measure it shows the current substitution status. @echo off if exist m:\nul echo The substitution has already been made if not exist m:\nul subst m: c:\math if not exist s:\nul subst s: c:\support subst 20. How to run a batch once a week (testing for the weekday) ============================================================ The crucial trick is to be able to put the weekday into an environment variable. For the full treatment see WEEKLY.BAT. The essential trick needed is below, that is capturing the weekday into a weekday_ environment variable. No auxiliary programs outside the normal MsDos commands are needed. @echo off echo.| date | find "Current" > tmp$$$.bat echo set weekday_=%%3> current.bat call tmp$$$ echo %weekday_% if "%weekday_%"=="Fri" echo Thank God it's Friday if exist tmp$$$.bat del tmp$$$.bat if exist current.bat del current.bat set weekday_= In fact, if you substitute %%4 for the %%3 in the above, you'll capture today's date. Neat, eh?