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STRINGS.COM (Version 2.0) Copyright (c) 1991, 1992 Douglas Boling ------------------------------------------------------------------------- First Published in PC Magazine December 22, 1992 (Utilities) ------------------------------------------------------------------------- STRINGS: The original STRINGS.COM removed the restrictions imposed by the DOS batch file language to give your batch files more versatility. This upgraded TSR version enhances a number of the original functions and implements more than 35 new ones. Batch Files Get Even Better With Our STRINGS 2.0 BY DOUGLAS BOLING The new version contains not only the batch file commands of the original utility, but 6 enhanced functions and 35 new ones as well. In all, as shown in Figure 1 (below) STRINGS now adds about 70 commands to the batch file language. (Some of these commands can be used from the DOS prompt as well.) Where the original STRINGS let you add a series of numbers, read a line from a file, or ask a user a question, STRINGS 2.0 includes additional functions that allow batch files to query the date and time, get the current country and codepage, and even read and write to memory locations. Perhaps the outstanding new feature of STRINGS 2.0 is that under DOS 3.3 or later it can now act as an extension to the DOS command processor, COMMAND.COM. This required rewriting the program so it could become a TSR. Once memory resident, since COMMAND.COM no longer has to search, load, and run the program, STRINGS's commands execute with the same speed as do such internal COMMAND.COM functions as COPY, RENAME, and DELETE. The new program itself bears the same name, STRINGS.COM, as its predecessor. That allows you to upgrade instantly simply by copying the new program over the old. To avoid confusion, I will refer to the original version of the utility as STRINGS1. If you have never used STRINGS1, reading through the original article will be helpful, but I'll try to explain enough here to make that unnecessary. To assemble the source you will need an assembler compatible with Microsoft's MASM 2.0. The commands to create STRINGS.COM are: MASM STRINGS; LINK STRINGS; EXE2BIN STRINGS STRINGS.COM USING STRINGS At first sight, the complete syntax for STRINGS.COM may seem dauntingly complex: STRINGS [/?][/M][/Q][/Pc][/Bn][/I][/U] [env var =] FUNCTION [Params] But it's a lot easier to use than it looks. One reason is that, in addition to this article, the on-screen help facilities are extensive. Simply enter STRINGS at the DOS prompt and you'll get an explanation of every item in the syntax line above. Entering STRINGS /? will give you a complete list of all the commands denoted by FUNCTION, and STRINGS /? FUNCTION will spell out the purpose, usage, and Prams (parameters) of each individual command. Note that in both of these last two commands the /? can be replaced by /HELP. Many STRINGS commands require no arguments; for these you just enter STRINGS FUNCTION For example, to return the last available drive letter you simply enter: STRINGS LASTDRIVE STRINGS will respond by displaying the last available drive letter on your system. For commands that do take input parameters, the arguments are separated by commas. For example, the command LEFT, which returns the first n characters (including spaces) of a string, has two parameters: the input string and the number of characters to return. Thus, STRINGS LEFT This is a string, 9 will return the left nine characters ``This is a". Note the comma separating the two parameters in the command line. The results of any STRINGS command can be assigned to an environment variable. Simply insert the name for the variable and an equals sign between STRINGS and FUNCTION. For example, by changing the previous example to STRINGS ANSWER =LEFT This is a string, 9 STRINGS will assign the string ``This is a'' to the environment variable ANSWER. As shown above, STRINGS has seven command line switches: /M, /Pc, /Q, /Bn, /I, /U and /?. The switch must be included on the command line before the environment variable or, if no variable is specified, before the command. By default, STRINGS stores variables in the Active environment, which is created by the current copy of COMMAND.COM. If the /M switch is used, however, STRINGS stores variables in the master environment, which is created by COMMAND.COM when DOS starts. In Windows, while each DOS box has its own Active environment, all share the Master environment. By using the /M switch, variables can be read by all programs, including those in individual Windows DOS boxes. The /M switch is also useful when you want to preserve a variable assignment you make while shelled out from a program, for the local environment is lost when you exit from DOS back into your application. Reverting to the previous example, to assign the results to the environment variable RESULT in the Master environment, the command would be STRINGS /M RESULT = LEFT This is a string, 9 The MASTERVAR command returns the string assigned to a variable in the Master environment. For example, the command STRINGS MASTERVAR RESULT returns the string assigned to the RESULT environment variable even if this command is executed in a different DOS box from the one that was used in previous examples! The /Pc (or Parse) switch tells STRINGS to use the c character rather than the comma to separate multiple parameters. This switch allows you to work with strings that contain commas. The /Q (or Quiet) switch, which was added in a maintenance release of STRINGS 1.0, prevents STRINGS from writing to the screen. This switch is useful if the STRINGS command may produce an error message that you don't want displayed on the screen. New in STRINGS 2.0 is the /Bn switch, which is used to change the number base that STRINGS uses to interpret numbers. STRINGS defaults to base 10 arithmetic, but by using the /B switch, you can set the base to any number from 2 to 16. Thus, while the statement STRINGS ADD 9, 1 returns the standard value 10, the statement STRINGS /B16 ADD 9, 1 returns the ``number'' A, since A in hexadecimal (base 16) is 10 in decimal. You'll want to use the /B switch working with several of the new STRINGS commands, where it is more appropriate to use hexadecimal than decimal numbers. If your system is running DOS 3.3 or later, using the /I switch installs STRINGS as a resident extension of COMMAND.COM. (How STRINGS actually accomplishes this will be discussed later.) Unlike most TSRs, which are installed at startup, STRINGS works best if it is installed only when and for as long as needed; it should be removed from memory once the batch file has completed in order to avoid wasting valuable system memory. To uninstall STRINGS, you simply use the /U switch. Installing STRINGS as a resident extension does not alter the syntax of any of its commands. The speed advantage is dramatic. The disadvantage, however, is that once installed, STRINGS (like all internal COMMAND.COM commands) cannot return an exit code to COMMAND.COM. This means that while STRINGS is resident, you can't use the handy IF ERRORLEVEL statement in .BAT files to test the result of STRINGS commands. If your batch file requires the error level codes returned by STRINGS, two solutions are available. The first and most obvious is simply not to install STRINGS at the start of the batch file. When not installed, STRINGS 2.0 returns the same error codes as STRINGS 1.0. The second solution is to specify explicitly the full path to the STRINGS.COM file. When a complete path is specified the resident copy of STRINGS will ignore the command, thus allowing COMMAND.COM to launch a second copy of STRINGS as a transient program. For example, since I keep STRINGS in my UTIL directory, I can force COMMAND.COM to launch a second copy of STRINGS with the command: C:\UTIL\STRINGS sub 12, 15 The use of the /? and /? FUNCTION switches to obtain on-line help was discussed earlier. It should be noted that on-line help is not available when STRINGS is installed in memory, since the help text would take up an additional 4,500 bytes of memory. To get help for a specific command while STRINGS is installed, simply specify the full path to force execution of a nonresident copy of STRINGS. STRINGS COMMANDS Providing a detailed explanation of the 70 functions shown in Figure 1 (see below) is not easy, so I've divided them into 6 groups: old commands enhanced for STRINGS 2.0, string handling, programmer's, data and time, system memory, and STRINGS management commands. The /? FUNCTION help screen will suffice for the functions in STRINGS1 if you haven't got access to the original article. (A copy of the original article (STRING1.DOC) is included in the archive STRING.ZIP). Six commands from STRINGS1 have been enhanced: CHAR, VAL, ASK, ADD, SUB, and MUL. In STRINGS1, the CHAR command was limited to returning the single ASCII character that corresponded to a decimal number. Now in STRINGS, CHAR can take up to ten parameters, so ten numbers can be converted into ten ASCII characters. For example, the command STRINGS CHAR 65, 66, 67 returns the string ABC. The VAL command has been similarly enhanced. An ASCII string passed to VAL will produce the series of up to ten decimal numbers that correspond to the characters in the string. The numbers will be separated by spaces. For example, the command STRINGS VAL Doug returns the string 68 111 117 103 When appropriate, this format can easily be converted into a series of hex bytes by using the /B16 switch. Note that because the capital and small letters have different ASCII values, VAL is inherently case-sensitive. The enhanced ASK function prints a string and waits for the user to enter a response. Its full syntax is: STRINGS [dest var =] ASK [Prompt string][,Max chars][,1=* echo 2=No echo] After entering the Prompt string as the first parameter, you specify the maximum number of characters the user can use to respond as the second. The maximum can be any number between 1 and 127. Although STRINGS works with strings up to 127 characters long, remember that DOS programs can only accept a command line with a total length of 127 characters. Thus, setting an environment variable to a long length may cause DOS to overflow the command line of a program that uses that variable. The third and final ASK parameter is a flag that tells STRINGS not to echo what the user types to the screen. This allows a .BAT file to prompt for a password without its becoming visible on the screen. When the third parameter is a 1, STRINGS echoes asterisks to the screen in place of the characters being typed. If the parameter is 2, STRINGS does not echo any characters to the screen. If neither flag is specified, the user response is echoed. Three of the math functions--ADD, SUB, and MUL--have been revised to allow you to add or multiply up to 10 different numbers in one STRINGS command. For the SUB command, up to nine numbers can be subtracted from the first number in the series. Thus, the command STRINGS SUB 10, 2, 1 returns the value 7, which is computed as 10 - 2 - 1. STRING HANDLING COMMANDS This first set of the new STRINGS commands goes to the root of the program's functionality; its ability to manipulate strings. The PARSE command separates a string into different sections and returns one of those sections. This command makes it easy to separate the different directory strings from the PATH environment variable, for example. The full syntax for PARSE is STRINGS [dest var =] PARSE String, section number, Separator char The three PARSE parameters are the string, the section number to return, and the separator character to be used to differentiate among sections. The small batch file, CHECKEX.BAT, (listed below in Figure 2) uses the PARSE command to search the PATH to determine the execution order of the program name you provide. This is exactly what COMMAND.COM does when it is asked to launch a program. On my machine, the command CHECKEX brief returned the list C:\UTIL\B.BAT C:\EDITORS\BRIEF\B.EXE This return discloses a problem: If DOS searches the full path, B.BAT will execute, but B.EXE never will. It seems I should rename that batch file! As shown by the STRINGS line in CHECKEX.BAT, the PARSE command here uses the PATH environment variable as the starting string. It uses the INDEX environment variable to run through the different directories in sequence. And it uses the semicolon to tell where one directory ends and the next one begins on the PATH statement. ADDCOMMAS is a simple command that inserts commas every three digits in a number you supply as its argument. If you enter STRINGS ADDCOMMAS 12345678 STRINGS will return 12,345,678 The REPEAT command simply creates a string that consists of the same character repeated n times. For example, the command STRINGS REPEAT 25, A will return a string with 25 As. The maximum value for n is 127. The FILEDATE command returns the date on a file. It takes filename as its only argument, and the date is returned in a mm-dd-yyyy format. The FILETIME command similarly returns the time when a file was last written, in a hh:mm:ss am/pm format. TRUEVER returns the true DOS version number, regardless of what is reported by the normal VER command. With the introduction of the SETVER device driver in DOS 5.0, you can trick programs into believing that they are running under a different version of DOS than they actually are. There are times, however, when you need to know the real DOS version: hence TRUEVER. The number returned is the major version number times 100, plus the minor version number. For example, in DOS 5.0 the number returned is 500. Although the SETVER device driver is only available on DOS 5.0 (and later), the TRUEVER command will still work under DOS versions 2.0 though 4.0; it simply returns the same value as does the STRINGS VER command. The FILES command returns the maximum number of files that can be open on the system at one time. This number is usually, but not always, the number shown in the FILES= statement in your CONFIG.SYS file. Programs such as Windows or Jeff Prosise's UMBFILES can change the maximum number of files, however, so FILES is a handy way to confirm that a program will have enough file handles to run. The LASTDRIVE command returns the last drive letter that can be assigned to a disk. This is usually set with the LASTDRIVE= line in the CONFIG.SYS file, but again, some programs can modify that value. LASTDRIVE is useful when a batch file must perform an action on all possible drives in the system. The CODEPAGE command allows batch files to determine the currently active codepage. The codepage number determines the character set your system uses. Most US systems use codepage 437, which is the standard character set. Codepage 850, on the other hand, replaces some of the graphic characters in the 437 codepage with characters used in European languages. To query the active codepage, simply enter STRINGS CODEPAGE. The COUNTRY command returns the country information for the system. Since DOS 2.0, parameters such as the currency symbol, thousands separator, and the date format can be configured for different countries. The table in Figure 3 (see below) shows what the COUNTRY command returns for different values of the first parameter, assuming you live in the U.S. Entering STRINGS BIOSDATE returns a string, normally containing the date, from address F000:FFF5h in the BIOS ROM. The command assumes the date will be in the first 8 bytes following the address, as it is in most PC compatibles. The command takes no arguments. The GETKEY command waits for the user to press a key then returns the ASCII value and its scan code. While the ASK command is limited to returning ASCII characters, GETKEY is also able to return non-ASCII keys such as the cursor keys and function keys. The codes are returned with the ASCII code first, followed by a space, followed by the scan code. It is at this point that you can use the PARSE command to operate separately on the ASCII and scan codes returned by the keystroke. The next four commands--AND, OR, XOR, and NOT--extend the math commands to logical operations. The AND command returns the logical AND of the parameters you supply. Likewise, the OR and XOR commands return the logical OR and exclusive OR of their respective parameters. Like the ADD, SUB, and MUL commands, the AND and OR commands can take up to ten parameters. XOR, of course, takes only two. The NOT command returns the one's complement of its single parameter. The CONVERT command, which converts a number to a different base, became necessary once the /B switch was introduced. This command takes two parameters: the number to be converted and the new number base. As with all commands, both the number and new base parameters are interpreted in the base specified in the /B switch. For example, to convert the hexadecimal (base 16) number 2FB to decimal, the command would be STRINGS /B16 CONVERT 2FB, A Note here that the second parameter, A, is not the character A, but rather the number 10, in hexadecimal. Going the other way, the command STRINGS CONVERT 763, 16 returns the hexadecimal number 2FB. (Because the default base for STRINGS is base 10, the /B switch is not required in this case.) TIME & DATE COMMANDS The next four commands return times and dates. The DAY function returns the current day of the week:STRINGS DAY will return Tuesday if today is Tuesday. As an added feature, if the DAY command is passed a number between 1 and 7, it returns the day corresponding to that number. STRINGS DAY 6 returns the string Friday, for example. The MONTH command is entirely similar to the DAY command, and again, if passed a number between 1 and 12, it returns the month corresponding to that number. The DATE command returns the current date in a mm-dd-yyyy format. The Time command similarly returns the current time in a hh:mm:ss am/pm format. Users requiring a different format for the time and date can easily use the multitude of STRINGS commands to present the data in any form they wish. SYSTEM MEMORY The enhanced STRINGS contains a number of commands that deal with system memory. MEMTOTAL returns the total conventional (DOS) memory available to the system, and MEMFREE returns the amount of conventional memory still available for use. Note, however, that the MEMFREE command will respond differently when STRINGS is installed as resident. COMMAND.COM does not release its memory when resident commands are executed, so if STRINGS is resident when this call is made, the amount of free conventional memory indicated will be small or nonexistent. The XMSTOTAL command returns the total amount of extended memory in the system, and XMSFREE returns the amount of free extended memory. Normally, extended memory is managed by an extended memory (XMS) manager, such as HIMEM.SYS. If no XMS manager is present, STRINGS uses a BIOS Int 15h call to determine the amount of extended memory. In this case, as there is no memory manager present to differentiate between free and used extended memory, both the XMSFREE and XMSTOTAL calls will return the same number. XMSVER returns the version of the XMS memory manager in use; if none is present, the command returns 0. Expanded memory is correspondingly queried with the EMSTOTAL, EMSFREE, and EMSVER commands. Again, if no expanded memory manager is installed, EMSVER will return 0. The final memory command is UMBLARGE. This command returns the size of the largest free upper memory block (UMB). UMBs are blocks of memory that reside between the video memory at A000h and the BIOS ROM at E000h or F000h. This command is useful for determining whether there is room in upper memory for TSRs. PROGRAMMER'S COMMANDS The next series of commands are designed for the PC programmer. They allow batch files to actually perform functions previously reserved for .COM and .EXE files. PEEK, the first of these commands, allows a batch file to read a series of bytes from memory. The syntax of the PEEK command is STRINGS [dest var=] PEEK Segment, Offset [,Number of bytes] [,Word flag] The first two command parameters are the segment and offset of the memory address to be read. The optional third parameter is the number of bytes to be read; if this parameter absent, STRINGS returns 1 byte. The fourth and final parameter is also optional. If it is 2, STRINGS will return the bytes read from memory in a 2-byte, or word, format. To illustrate, in order to see which shift keys are pressed, you can use the PEEK command to read the keyboard status bytes at 40:17 and 40:18 hex. The command would be STRINGS /b16 PEEK 40, 17, 2. The complementary POKE command writes data directly to memory. Again, the first parameter is the segment and the second is the offset of the address. The remaining parameters, up to an additional eight, are the bytes to write to memory. Note that while these bytes are being written, interrupts are disabled so the system doesn't read partially written data. The following short batch file uses the PEEK, AND, and POKE commands to turn off the keyboard NumLock. STRINGS /b16 shift = PEEK 40, 17 STRINGS /b16 shift = AND %SHIFT%, DF STRINGS /b16 POKE 40, 17, %SHIFT% SET shift= You could also use the POKE command to overwrite the DOS command interrupt vector (Interrupt 21) with zeros, the command would be STRINGS /B16 POKE 0, 84, 0, 0, 0,0 Don't try this example, however, for it will surely lock up your machine! As this last example illustrates, POKE--and other programming commands that will be discussed shortly--can easily be misused and thereby cause harm. So make sure you fully understand a command before you use it. The IN and OUT commands give batch files the ability to read and write to system I/O (Input/Output) ports. It is through these ports that the system talks to disk drive controllers and to devices connected to serial and/or parallel ports. The IN command takes only one parameter, namely, the address of the I/O port. This address is the first of the OUT command's two parameters, the second being the data byte to write to that port. An amusing example that demonstrates the use of the IN and OUT commands is provided by the batch files NOIZE and MARY, which are listed below in Figure 4. NOIZE.BAT plays a note on the PC speaker by toggling the speaker control bits in the keyboard control I/O port (I/O address 61h). The proper timing for the note is determined by using PC hardware timer 3. MARY.BAT calls NOIZE.BAT to play the familiar ``Mary had a little lamb.'' My thanks to Neil Rubenking for this entertaining example. The INTERRUPT command is easily the most powerful--and therefore dangerous--command in the STRINGS repertoire. The command calls an interrupt and returns the values of the registers. The ten parameters for this command specify the interrupt number and the values of most of the processor registers at the time the interrupt is called. Its syntax is the following: STRINGS INTERRUPT Int Number, AX, BX, CX, DX, DI, SI, BP, DS, ES The string returned is a series of numbers, separated by spaces, that represent the value in each of the registers at the time the interrupt returns. The format for the returned string is AX BX CX DX DI SI BP DS ES Flags The Flags register contains such flags as Carry, Zero, Sign, and Interrupt Enable. Just as a value is returned for each of the other registers, a value is also returned for the Flags register. It is the responsibility of the batch program to examine the value returned for the Flags register to determine the state of any flags that might be important. For this purpose, the AND and OR commands often prove useful. An example of this complex command in action will be helpful. Suppose you want to know the address of the InDOS flag. The newly documented function for getting the InDOS address is Interrupt 21, AH = 34. The STRINGS command to enter would be STRINGS /B16 INTERRUPT 21, 3400, 0, 0, 0, 0, 0, 0, 0, 0 The /B16 switch is used to tell STRINGS to ``talk'' in hexadecimal, which is handy because most PC programming is done in base 16. The 21 indicates that you want STRINGS to call Interrupt 21h, the DOS command dispatcher. The 3400 indicates that AX is to be loaded with 3400h when the interrupt is called. In fact, you only need to load AH (with 34h), but the command has no way of loading the individual byte halves of the registers. Thus, you end up loading AX with 3400, which puts 34 in AH and 00 in AL. The remaining registers for this interrupt are not important, and actually they don't have to be included at all. STRINGS loads 0 in the registers not specified. On my machine running MS-DOS 5.0, the command above returns the string 3400 321 0 0 0 0 0 0 116 7246 The INTERRUPT command always returns a string with ten numbers, each separated by a space. Because the /B16 switch was used, all the values are in hexadecimal. The first number, 3400, is the value of the AX register when the interrupt returns. The important values, however, are 321, the value of BX on the return; and 116, which is the returned value of ES. The MS-DOS Programmer's Reference indicates that the address of the InDOS flag will be returned in ES:BX. You can now use the PEEK command to check the state of the InDOS flag. That command would look like this: STRINGS /B16 PEEK 116 321 Although knowing the address of the InDOS flag has little use for batch file programming, other interrupts can come in quite handy. The undocumented interrupt 21 AX=5200 returns a pointer to DOS's list of lists. This pointer is quite useful for checking out the current state of the machine. Shortly I'll present a batch file that uses the list of lists to determine the current memory usage for the system. The final programmer's command is SCAN. This command searches memory for a series of bytes. The segment to search and the starting offset are specified in the first two parameters. The remaining parameters (up to an additional eight) are the bytes to use in the search. For example, to search the segment 23h for the byte series 10 20 30 40 the command would be STRINGS /B16 SCAN 23, 0, 10, 20, 30, 40 Since SCAN searches only the segment specified, additional SCAN commands are needed for any searches beyond the original segment. When used in conjunction with the improved VAL command, SCAN can search for an ASCII string in memory. An example is shown in the following batch code fragment, which searches the DOS kernel for the string ``NUL": STRINGS /B16 VALSTR = VAL NUL STRINGS /B16 /P SCAN 116 0 %VALSTR% As previously discussed, the VAL command returns the ASCII numbers for each of the characters in the first parameter. In this case, because the /B16 switch is used, VAL returns the numbers 4E 55 4C as a series of hex bytes. These bytes are assigned to the VALSTR environment variable. The new InDOS command mentioned above starts at offset 0 and uses the VALSTR environment variable for its remaining arguments. On my machine, this fragment returns the address 116 52, which is the address for the NUL device driver name. That address is important because the NUL device driver is the first in the DOS device driver chain. Two additional notes about this batch fragment are in order. First, the lack of commas separating the parameters in the SCAN command is not a typo. The /P switch is used here to change the parse character to a space. This is convenient, since the VAL command returns its numbers separated by spaces. The second important detail concerns the consistent use of the /B switch. While it may not seem that the /B switch would be needed for either command, if it is used in the VAL command it must be used in the SCAN command. Since VAL uses a /B16 switch, it returns its numbers in hex. Because the result from the VAL command is used in the SCAN command, SCAN must use the same base. Why was the /B16 switch used in the first place? Remember that the DOS segment returned by the INTERRUPT command was returned in hexadecimal, which forced the use of the /B switch since we used that number. Just follow this simple rule: If parameters are shared across STRINGS commands, they should use the same base, or you should use the CONVERT command to change the parameters to the proper base. STRINGS MANAGEMENT The final group of new STRINGS commands are to manage STRINGS itself. STRINGSVER returns the version of STRINGS currently being used. Since this command did not exist in the first version of STRINGS, calling it with STRINGS1 will result in an error message and a return code of 1. If STRINGSVER returns a nonzero ERRORLEVEL code, then STRINGS 1.x is running. For the present version of STRINGS, the STRINGSVER command returns the ASCII string 200 and a return code of 0. The INSTALLED command returns a 1 if STRINGS is currently installed as a TSR extension to COMMAND.COM. If STRINGS is not installed, a 0 is returned. This command is useful for those situations in which a STRINGS command might produce different results if the utility were installed. MEMFREE represents one such case, and the use of return codes may be another. INSIDE STRINGS For the most part, the enhanced version of strings simply involved adding procedures for the new functions. The main change to the program itself was the rewriting of the command parsing routine to use less memory. This was necessary so that STRINGS could be turned into a TSR. Of greatest programming interest, however, is the hook into COMMAND.COM's internal command dispatcher. In Undocumented DOS, coauthor Jim Kyle has an informative chapter on command interpreters. It describes an undocumented ``back door'' into COMAND.COM that allows TSRs to hook into the internal command dispatcher. This back door was first included in DOS 3.3 so that DOS's APPEND command could check on any subsequent APPEND commands. Fortunately for programmers, that door has remained open in all later DOS releases. When you enter a command at the DOS command line, COMMAND.COM must determine whether the command is an internal function to be executed or an external program that must be launched. Before making its decision, COMMAND.COM calls the Multiplex Interrupt (Int 2Fh) with AX equal to AE00h. At the time of the call, DX is loaded with FFFFh, BX is pointing to a buffer that contains an exact replica of the command line just typed, and SI points to a buffer that contains the potential command in uppercase preceeded by a length byte. TSRs such as STRINGS that hook into this call must compare the command to which SI points with the command they wish to handle. For STRINGS, that means checking to see whether SI is pointing to the ASCII string "STRINGS". A TSR that wants to claim the command puts 0FFh in AL, copies the comand line pointed to by BX into an internal buffer, and returns to COMMAND.COM. Otherwise the TSR must pass the Multiplex request down the interrupt chain with all registers unmodified. If a TSR claims the command, COMMAND.COM calls the Multiplex Interrupt again, this time with AX loaded with AE01h. Having claimed it, the TSR must now execute the command. While most of the registers during this call are the same as in the AE00h call, Kyle recommends that a TSR should copy the buffer from the earlier AE00h call because not all the registers are explicitly loaded before the AE01h call. Once the command has been completed, the TSR should zero the size byte in the buffer to which SI points. This tells COMMAND.COM that the command has been processed. While STRINGS doesn't provide every possible function a batch file might want, the inclusion of such commands as PEEK, POKE, and INTERRUPT allow the programmer to create just about any command. An an example of this power is shown in BATMEM.BAT, which is listed below in Figure 5. BATMEM scans the DOS memory blocks and displays the blocks that are being used as well as the ones that are free. BATMEM is similar to the MEM command that has been included in DOS since version 4.0. Among the STRINGS functions BATMEM uses are INTERRUPT, PARSE, CHAR, PEEK, and ADDCOMMAS. Notice that in BATMEM, STRINGS is installed with /I at the beginning of the batch file and removed with /U at the end. These two switches double the execution speed. If you don't want STRINGS installed and removed, simply delete the /I and /U switches; the remainder of the batch file will be unaffected. Programs like BATMEM give but a taste of the world STRINGS opens to enterprising batch file writers. To supplement STRINGS own commands, you may wish to acquire Michael J. Mefford's excellent BATCHMAN utility in the January 30, 1990 issue of PC Magazine. Like STRINGS, BATCHMAN is available on PC MagNet. The ability to perform low-level actions, coupled with the convenient features of STRINGS's high-level commands, provide a wealth of new opportunities for the once-lowly batch file. Try STRINGS, and your batch files will never be the same. ---------------------------------------------------------------------------- DOUGLAS BOLING IS A CONTRIBUTING EDITOR TO PC MAGAZINE. ---------------------------------------------------------------------------- STRINGS COMMANDS FUNCTION AND SYNTAX RETURNS New 2FCHECK n or Alias Returns status of programs hooked to the Multiplex Interrupt. Enhanced ADD n1, n2[,n3][,n4][,n5] The sum of the parameters. [,n6][,n7][,n8][,n9][,n10] New ADDCOMMAS n n parsed with commas every 3 digits. New AND n1, n2[,n3][,n4][,n5] The logical AND of the [,n6][,n7][,n8][,n9][n10] parameters. Enhanced ASK [Prompt string] [, Max chars][,1=No echo] A response from a user. New BIOSDATE The date for the ROM BIOS. Enhanced CHAR c[c][c][c][c] [c][c][c][c][c][c] ASCII number of character. New CODEPAGE The activecode page. Requires DOS 3.3 or later. New CONVERT n, New Base A number with the specified base. New COUNTRY The country code for the system. New DATE The current date in mm-dd-yyyy format. New DAY [Index (1=Sunday, 2=Mon] The name of the day of the week. DIV n, n The quotient of two numbers. New EMSFREE The amount of free expanded memory. New EMSTOTAL The amount of expanded memory. New EMSVER The version of the expanded memory driver. ENVFREE Bytes free in the environment. ENVSIZE The size of the environment. New FILEDATE Filename The date of a file. FILEDIR Filename The directory of a filename. FILEDRIVE Filename The drive of a filename. FILEEXT Filename The file extension. FILENAME Filename The filename. New FILES The total number of files that can be open. FILESIZE Filename The size of a file. New FILETIME Filename The time of a file. FIND String, Findstring The position of Findstring in String. FINDC String, Findstring The position of Findstring in String. Case sensitive. New GETKEY The scan code and ASCII value of next key pressed. New HELP [Strings Command] The help text for the specified STRINGS command. New IN Port number A byte from an I/O port. New INSTALLED A non-zero number if Strings installed as TSR. New INTERRUPT Int n, AX, BX, CX, DX, DI, SI, BP, DS, ES The registers from an interrupt. Dangerous! INWIN 1 if Windows running. New LASTDRIVE The letter of the last possible drive. LEFT String, n The left n characters. LENGTH String The String length. LINESIZE Filename The number of lines. LOWER String The string in all lowercase. MASTERENV The address of the master environment MASTERVAR Variable Name A variable from the Master environment. New MEMFREE The largest block of free conventional memory. New MEMTOTAL The amount of conventional memory. MID String, Start c, Length The middle n characters. New MONTH [Index (1=January)] The name of the month Enh MUL n1, n2[,n3][,n4][,n5] [,n6][,n7][,m8][,n9][,n10] The product of the parameters. New NOT n The logical NOT of n. New OR n1, n2[,n3][,n4][,n5] [,n6][,n7][,n8][,n9][,n10] The logical OR of the parameters. New OUT Port n, Output byte Writes a byte to an I/O port. New PARSE String, Token n, Token separator char The nth token from a string. New PEEK Segment, Offset [, n bytes [,Word flag]] A series of bytes from memory. New POKE Segment, Offset, b1[,b2][,b3][,b4] [,b5][,b6][,b7][,b8] Writes up to 8 bytes to memory. READ Filename, line number A line from a file. New REPEAT n of chars, c A string of n characters c. RIGHT String, n The right n characters. New SCAN Segment, Starting Offset, b1 [,b2] The offset of a series of bytes in memory. Enh SUB n1, n2[,n3][,n4][,n5] [,n6][,n7][,n8][,n9][,n10] The difference of two numbers. New TIME The current time. TRUENAME Filename The complete filename. New TRUEVER The true DOS verison. Requires DOS 5.0 or later. New UMBLARGE The largest block of free upper memory. UPPER String The string in all uppercase. Enh VAL n1, n2[,n3][,n4][,n5] [,n6][,n7][,n8][,n9][,n10] ASCII characters for a number. VER The DOS version number. WRITE Filename, String Appends a string to the end of a file. New XMSFREE The amount of free extended memory. New XMSTOTAL The amount of extended memory. New XMSVER The version of the extended memory driver. New XOR n, n The exclusive OR of two numbers. Figure 1: All commands shown above begin with STRINGS [dest var =]. In the listing, n designates a number, c a character, and b a byte. ---------------------------------------------------------------------------- CHECKEX.BAT rem---------------------------------------------------- rem CHECKEX.BAT - Scans the path for a program name. rem---------------------------------------------------- @echo off SET index=1 if exist %1.com echo %1.com if exist %1.exe echo %1.exe if exist %1.bat echo %1.bat :loop STRINGS pdir = PARSE %path%, %index%,; IF . == .%pdir% GOTO exit if exist %pdir%\%1.com echo %pdir%\%1.com if exist %pdir%\%1.exe echo %pdir%\%1.exe if exist %pdir%\%1.bat echo %pdir%\%1.bat STRINGS index = ADD %index%, 1 GOTO loop :exit SET index= SET pdir= Figure 2: CHECKEX.BAT shows the execution priority order for a program name that might be present on a path in .COM, .EXE, and .BAT forms. ------------------------------------------------------------------------ COUNTRY CODES ================================================================== First Parameter Value Returns Comments -------------------------------------------------------------------- No parameter Country Code Active country code 0 Date Format 0 = mm-dd-yyyy 1 Currency Symbol $ for the US 2 Thousands Separator , for the US 3 Decimal Separator . for the US 4 Date Separator - for the US 5 Time Separator : for the US 6 Currency Format 0 for the US 7 Currency Places 2 for the US 8 Time Format 0 = 12-hour format 9 Data Separator , for the US Figure 3: These are the different values returned when 1 is supplied as the parameter for the COUNTRY command. ------------------------------------------------------------------------ NOIZE.BAT @ECHO OFF REM ------------------------------------------------------------ REM NOIZE.BAT - by Neil Rubenking REM REM Enter a frequency as its command line parameter and it REM starts a note of that frequency. Enter NO parameter and it REM shuts the speaker up. REM ------------------------------------------------------------ IF '%1'=='' GOTO Stop STRINGS inv=DIV 1193180,%1 STRINGS inv=CONVERT %inv%,16 STRINGS inv=RIGHT 0000%inv%,4 STRINGS Hi=LEFT %inv%,2 STRINGS Lo=RIGHT %inv%,2 STRINGS /b16 OUT 43,B6 STRINGS /b16 OUT 42,%lo% STRINGS /b16 OUT 42,%hi% STRINGS /b16 AL=IN 61 STRINGS /b16 AL=OR %AL%,3 STRINGS /b16 OUT 61,%AL% GOTO End :Stop STRINGS /b16 AL=IN 61 STRINGS /b16 AL=AND %AL%,FC STRINGS /b16 OUT 61,%AL% :End SET al= SET inv= SET hi= SET lo= @ECHO OFF REM ------------------------------------------------------------ REM MARY.BAT - by Neil Rubenking REM REM Plays a familar tune REM ------------------------------------------------------------ STRINGS /I /Q CALL NOIZE 330 CALL NOIZE 294 CALL NOIZE 262 CALL NOIZE 294 CALL NOIZE 330 CALL NOIZE 330 CALL NOIZE 330 CALL NOIZE 330 CALL NOIZE 294 CALL NOIZE 294 CALL NOIZE 294 CALL NOIZE 294 CALL NOIZE 330 CALL NOIZE 392 CALL NOIZE 392 CALL NOIZE 392 CALL NOIZE STRINGS /U /Q Figure 4: NOIZE.BAT and MARY.BAT combine to play "Mary Had a Little Lamb." -------------------------------------------------------------------------- BATMEM.BAT @echo off rem ------------------------------------------------------------- rem rem A batch file that returns a memory scan rem BATMEM.BAT rem Copyright 1992 Douglas Boling rem rem ------------------------------------------------------------- rem rem First, get the pointer to the list of lists rem strings /i /b16 iret = interrupt 21, 5200 strings /b16 lloff = parse %iret%, 2 strings /b16 llseg = parse %iret%, 9 set iret= rem rem First memory block kept at ListOfList - 2 rem strings /b16 lloff = sub %lloff%, 2 strings /b16 memseg = peek %llseg%, %lloff%, 2, 2 echo. echo Block Owner Size Program echo -------------------------------- strings /b16 totalmem = add %memseg%, 1 set freemem=0 :loop rem rem Parse the memory arena header rem strings /b16 memtype = peek %memseg%, 0, 1 strings /b16 memowner = peek %memseg%, 1, 2, 2 strings /b16 memsize = peek %memseg%, 3, 2, 2 strings /b16 memtemp = peek %memseg%, 8, 8 strings /b16 /p memtemp = char %memtemp% strings /b16 memseg = add %memseg%, 1 rem rem If block not PSP, don't print block name rem set memname= set diff=-1 strings /b16 /q diff = sub %memseg%, %memowner% if .%diff% == .0 goto skip1 goto skip2 :skip1 set memname=%memtemp% :skip2 if NOT %memowner% == 0000 goto skip3 set memowner=FREE strings /b16 freemem = add %freemem%, %memsize% :skip3 rem rem OK, print the results rem echo %memseg% %memowner% %memsize% %memname% strings /b16 memseg = add %memseg%, %memsize% strings /b16 totalmem = add %memsize%, %totalmem% strings /b16 totalmem = add %totalmem%, 1 if %memtype% == 4D goto loop echo. strings /b16 memsize = mul %memsize%, 10 strings /b16 memsize = convert %memsize%, A strings memsize = addcommas %memsize% strings /b16 totalmem = mul %totalmem%, 10 strings /b16 totalmem = convert %totalmem%, A strings /u totalmem = addcommas %totalmem% echo %totalmem% bytes total conventional memory echo %memsize% largest program executable size echo. rem rem Done, clean up all vars rem set llseg= set lloff= set memseg= set memowner= set memsize= set memtype= set memname= set memtemp= set freemem= set totalmem= set diff= Figure 5: BATMEM.BAT produces a list of the DOS memory segments. ------------------------------------------------------------------------