NAME tclvars - Variables used by Tcl DESCRIPTION The following global variables are created and managed automatically by the Tcl library. Except where noted below, these variables should normally be treated as read- only by application-specific code and by users. env This variable is maintained by Tcl as an array whose elements are the environment variables for the process. Reading an element will return the value of the corresponding environment variable. Setting an element of the array will modify the corresponding environment variable or create a new one if it doesn't already exist. Unsetting an ele- ment of env will remove the corresponding environ- ment variable. Changes to the env array will affect the environment passed to children by com- mands like exec. If the entire env array is unset then Tcl will stop monitoring env accesses and will not update environment variables. errorCode After an error has occurred, this variable will be set to hold additional information about the error in a form that is easy to process with programs. errorCode consists of a Tcl list with one or more elements. The first element of the list identifies a general class of errors, and determines the for- mat of the rest of the list. The following formats for errorCode are used by the Tcl core; individual applications may define additional formats. ARITH code msg This format is used when an arithmetic error occurs (e.g. an attempt to divide by zero in the expr command). Code identifies the pre- cise error and msg provides a human-readable description of the error. Code will be either DIVZERO (for an attempt to divide by zero), DOMAIN (if an argument is outside the domain of a function, such as acos(-3)), IOVERFLOW (for integer overflow), OVERFLOW (for a floating-point overflow), or UNKNOWN (if the cause of the error cannot be deter- mined). CHILDKILLED pid sigName msg This format is used when a child process has been killed because of a signal. The second element of errorCode will be the process's identifier (in decimal). The third element will be the symbolic name of the signal that caused the process to terminate; it will be one of the names from the include file sig- nal.h, such as SIGPIPE. The fourth element will be a short human-readable message describing the signal, such as ``write on pipe with no readers'' for SIGPIPE. CHILDSTATUS pid code This format is used when a child process has exited with a non-zero exit status. The second element of errorCode will be the pro- cess's identifier (in decimal) and the third element will be the exit code returned by the process (also in decimal). CHILDSUSP pid sigName msg This format is used when a child process has been suspended because of a signal. The second element of errorCode will be the pro- cess's identifier, in decimal. The third element will be the symbolic name of the signal that caused the process to suspend; this will be one of the names from the include file signal.h, such as SIGTTIN. The fourth element will be a short human-read- able message describing the signal, such as ``background tty read'' for SIGTTIN. NONE This format is used for errors where no additional information is available for an error besides the message returned with the error. In these cases errorCode will con- sist of a list containing a single element whose contents are NONE. POSIX errName msg If the first element of errorCode is POSIX, then the error occurred during a POSIX ker- nel call. The second element of the list will contain the symbolic name of the error that occurred, such as ENOENT; this will be one of the values defined in the include file errno.h. The third element of the list will be a human-readable message correspond- ing to errName, such as ``no such file or directory'' for the ENOENT case. To set errorCode, applications should use library procedures such as Tcl_SetErrorCode and Tcl_Posix- Error, or they may invoke the error command. If one of these methods hasn't been used, then the Tcl interpreter will reset the variable to NONE after the next error. errorInfo After an error has occurred, this string will con- tain one or more lines identifying the Tcl commands and procedures that were being executed when the most recent error occurred. Its contents take the form of a stack trace showing the various nested Tcl commands that had been invoked at the time of the error. tcl_library This variable holds the name of a directory con- taining the system library of Tcl scripts, such as those used for auto-loading. The value of this variable is returned by the info library command. See the library manual entry for details of the facilities provided by the Tcl script library. Normally each application or package will have its own application-specific script library in addition to the Tcl script library; each application should set a global variable with a name like $app_library (where app is the application's name) to hold the network file name for that application's library directory. The initial value of tcl_library is set when an interpreter is created by searching several different directories until one is found that con- tains an appropriate Tcl startup script. If the TCL_LIBRARY environment variable exists, then the directory it names is checked first. If TCL_LIBRARY isn't set or doesn't refer to an appro- priate directory, then Tcl checks several other directories based on a compiled-in default loca- tion, the location of the binary containing the application, and the current working directory. tcl_patchLevel When an interpreter is created Tcl initializes this variable to hold a string giving the current patch level for Tcl, such as 7.3p2 for Tcl 7.3 with the first two official patches, or 7.4b4 for the fourth beta release of Tcl 7.4. The value of this vari- able is returned by the info patchlevel command. tcl_pkgPath This variable holds a list of directories indicat- ing where packages are normally installed. It typ- ically contains either one or two entries; if it contains two entries, the first is normally a directory for platform-dependent packages (e.g., shared library binaries) and the second is normally a directory for platform-independent packages (e.g., script files). Typically a package is installed as a subdirectory of one of the entries in $tcl_pkgPath. The directories in $tcl_pkgPath are included by default in the auto_path variable, so they and their immediate subdirectories are automatically searched for packages during package require commands. tcl_platform This is an associative array whose elements contain information about the platform on which the appli- cation is running, such as the name of the operat- ing system, its current release number, and the machine's instruction set. The elements listed below will always be defined, but they may have empty strings as values if Tcl couldn't retrieve any relevant information. In addition, extensions and applications may add additional values to the array. The predefined elements are: machine The instruction set executed by this machine, such as PPC, 68k, or sun4m. On UNIX machines, this is the value returned by uname -m. os The name of the operating system running on this machine, such as Win95, MacOS, or SunOS. On UNIX machines, this is the value returned by uname -s. osVersion The version number for the operating system running on this machine. On UNIX machines, this is the value returned by uname -r. platform Either windows, macintosh, or unix. This identifies the general operating environment of the machine. tcl_precision If this variable is set, it must contain a decimal number giving the number of significant digits to include when converting floating-point values to strings. If this variable is not set then 6 digits are included. 17 digits is ``perfect'' for IEEE floating-point in that it allows double-precision values to be converted to strings and back to binary with no loss of precision. tcl_rcFileName This variable is used during initialization to indicate the name of a user-specific startup file. If it is set by application-specific initializa- tion, then the Tcl startup code will check for the existence of this file and source it if it exists. For example, for wish the variable is set to ~/.wishrc for Unix and ~/wishrc.tcl for Windows. tcl_rcRsrcName This variable is only used on Macintosh systems. The variable is used during initialization to indi- cate the name of a user-specific TEXT resource located in the application or extension resource forks. If it is set by application-specific ini- tialization, then the Tcl startup code will check for the existence of this resource and source it if it exists. For example, the Macintosh wish appli- cation has the variable is set to tclshrc. tcl_version When an interpreter is created Tcl initializes this variable to hold the version number for this ver- sion of Tcl in the form x.y. Changes to x repre- sent major changes with probable incompatibilities and changes to y represent small enhancements and bug fixes that retain backward compatibility. The value of this variable is returned by the info tclversion command. KEYWORDS arithmetic, error, environment, POSIX, precision, subpro- cess, variables