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7 Global Variables Global variables are just a way of saving character strings for later use. They are referred to as "global" because they are accessible from within all batch programs as well as interactively. MacDOS automatically generates and uses some variables called "System Variables". Creating and Setting Variables You can set global variables interactively or in batch programs with the command SET. When you SET a variable for the first time, MacDOS automatically creates it. The format of SET is very simple: set variable name=whatever string you like Any string can be used to name such user-defined variables, but be aware that: • If you include a percent sign, this will confuse MacDOS when you try to use the variable in a command, because percent signs are used to access the value of variables (see below). • If you include double quotes or other special characters like colons, slashes, and backslashes you might run into problems later when you use the variable in batch programs. At the very least, you will find it confusing when reading your program. • When recording a variable name, MacDOS ignores leading and trailing spaces and tabs. That is, you will not be able to create a variable name which begins or ends with blanks. • MacDOS also simplifies all sequences of spaces and tabs found within variable names, so that words forming a variable name are always separated by single spaces. The string which follows the equal sign is stored as it is, including leading and trailing blanks. When you SET an existing variable, MacDOS simply replaces the current value with the new one. Displaying and Removing Variables To display a list of the existing variables and their content, just type the command SET without parameters. MacDOS then displays all the variables in the order in which they were created. You can also display the string stored in a single variable by typing: ECHO %varName% When you do not need a user-defined variable anymore, it is a good practice to remove it from the system. To do so, SET the variable to an empty string by typing return immediately after the equal sign. System variables are special, in that they cannot be removed from the system. When you SET a system variable to the empty string, MacDOS does not remove it but sets it back to its default value. Retrieving Variables You can access the string stored in a variable by inserting in a command the variable name enclosed between a pair of percent signs. For example, you can define the variable HOME by executing SET HOME=%WHERE% and then attach back to that folder with CHDIR %HOME% . Similarly, if the variable RET_LBL contains a label name, you can jump to that label with the command GOTO %RET_LBL% . If you type two consecutive percent signs, MacDOS recognises that you are not attempting to de-reference a variable or a replaceable parameter and handles the pair of characters as a single percent sign. Operations on Variables MacDOS provides a series of commands which let you manipulate global variables. They are: INCR, DECR, SSTR, and TOUPPER. If you need to keep the original value, use SET to save it before executing any of these commands. INCR INCR has the purpose of incrementing numeric values, adding numbers, and extending or concatenating alphanumeric strings. incr numVar incr numVar by 7 incr numVar by -3 are examples in which INCR is used to increment the numeric value stored in the global variable numVar. In the last example, the final value is actually less than the initial one, because the increment is negative. incr numVar by %anotherNumVar% shows how INCR can be used to add anotherNumVar to numVar. incr var by " append this" incr -var by "prepend this " incr var by anAlphaVar incr alphaVar by 3 incr -alphaVar by 3 are examples of how INCR can be used to attach strings to each other. In the last two examples, three spaces are appended and prepended to alphaVar respectively. DECR DECR has the purpose of decrementing numeric values, subtracting numbers, and truncating or subtracting alphanumeric strings. decr numVar decr numVar by 7 decr numVar by -3 are examples in which DECR is used to decrement the numeric value stored in the global variable numVar. In the last example, the final value is actually greater than the initial one, because the decrement is negative. decr numVar by %anotherNumVar% shows how DECR can be used to subtract anotherNumVar from numVar. decr var by " remove this from the end" decr -var by "remove this from the beginning" decr var by anAlphaVar decr alphaVar by 3 decr -alphaVar by 3 are examples of how DECR can be used to subtract strings from each other. In the last two examples, the three last and first characters are removed from alphaVar respectively. SSTR SSTR extracts a substring from a variable (the name SSTR stands for SubSTRing). In order to identify what should remain and what should be removed, SSTR uses a string as delimiter. Its format is: sstr var delim where delim is the string which SSTR uses to split the variable. By default, SSTR searches for the delimiter from the beginning of the variable string, and extracts the substring on the left of the delimiter. Optionally, you can direct SSTR to search from the end rather than from the beginning, and to keep the substring on the right of the delimiter rather than on its left. TOUPPER TOUPPER converts the value of a variable to upper case. It is useful when you want to compare strings and filenames ignoring upper and lower cases. Note that diacritical marks and international characters are converted correctly: ü to Ü, æ to Æ, ø to Ø, etc. System and Special Variables Currently, MacDOS implements seven system variables: PROMPT, DIRCMD, PATH, WHERE, CREATOR, QUOTE, and FONTSIZE. MacDOS also uses the variables DOSERR, SHOWAE, and TIMEOUT, which behave like user-defined variables and can therefore be removed. PROMPT stores the format of the string displayed by MacDOS to prompt you for a new command. By using a dollar sign as an escape character, PROMPT can memorise requests to display special information, like the current date and time, the specification of the current folder, the current volume ID, and the MacDOS version. Instead of setting the variable PROMPT with the command SET, you should use the command PROMPT. This would ensure that you set the prompt string to a valid value. By default, the prompt string consists of the current volume ID followed by a "greater than" sign (PROMPT=$n$g). Please refer to the command reference section on PROMPT for a list of dollar-options. DIRCMD stores the default options for the commands DIR and TREE. By default, DIR and TREE list all visible files and folders in extended format, non recursively, non sorted, and not case sensitive. Please refer to the command reference section on DIR for a list of valid options. PATH stores the list of folders that MacDOS searches when looking for batch programs, applications, AppleScripts, MacDOS extensions, and abbreviation files. The folder specifications are separated by semicolons. When you direct MacDOS to execute a program or look for an abbreviation file, MacDOS searches the current folder for a file of the appropriate type with the requested name. It then searches the folders specified in PATH, scanning the list from left to right. MacDOS initialises the system variable PATH to the empty string. Therefore, by default MacDOS only searches the current folder. To set the variable PATH you can also use the command with the same name. To add a folder specification to the existing list, you can execute any of the following commands: set path=%path%;newFolderSpec path %path%;newFolderSpec incr path by ;newFolderSpec WHERE always contains the specification of the current folder. MacDOS updates WHERE every time you change volume or directory. This variable lets you "go back" to the initial folder after using CHDIR to attach to other folders and volumes. To do this, you must save WHERE by copying it to another variable before attaching to the new folder. For example: set back=%where% chdir anotherFolder ... chdir %back% CREATOR stores the file creator that MacDOS uses when creating new files. By default, the creator is 'ttxt' (ie. TeachText). You can set it to the creator of your preferred editor or word processor. You can also set it to 'mDOS' if you want to create batch programs. The alternative would be to create the files and then use REN to change their creators. Note that MacDOS only uses the first four characters of this variable. Therefore, you can use the rest of the line for comments. QUOTE stores the character used by MacDOS to delimit file and folder names which contain spaces and other special characters. The default is the double quote character. By changing QUOTE, you can access file names which contain double quote characters: set quote=# rename #with "quotes"# #without quotes# del bla"bla set quote= FONTSIZE stores the point size of the characters used in the console window. The default is 9, but the values 12, 18, 24, and 36 are also legal. Other values are rounded down to one of the permitted sizes, except values lower than 9 which are rounded up. DOSERR stores the code of the last error. As error codes are always positive numbers (see appendix A), zero can be used as a no-error condition. MacDOS updates this variable whenever an error (not a warning) occurs, but does not reset it when a command completes successfully. Therefore, it is your responsibility to remove it or initialise it to zero. You can obtain the error message corresponding to a particular error code with the command SHOW. SHOWAE tells MacDOS whether it should display incoming Apple Events. MacDOS only checks whether this variable exists or not, completely ignoring its value. For a list of Apple Events supported by MacDOS, please refer to the section "MacDOS Scripting". TIMEOUT Stores the number of seconds that MacDOS waits for piped messages to go through a chain of MacDOS extensions. Please refer to the section "MacDOS Extensions" for the details.