tclvars(n) Tcl ( ) tclvars(n)
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NAME
tclvars - Variables used by Tcl
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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 element of env will remove the
corresponding environment variable. Changes to the env
array will affect the environment passed to children by
commands 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 format 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 precise 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), |
OVERLFLOW (for a floating-point overflow), or |
UNKNOWN (if the cause of the error cannot be |
determined).
CHILDKILLED pid sigName msg
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tclvars(n) Tcl ( ) tclvars(n)
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 signal.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 process'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 process'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-readable
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 consist 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 kernel 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
corresponding 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_PosixError, |
or they may invoke the error command. If one of these
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tclvars(n) Tcl ( ) tclvars(n)
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 contain
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_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.
KEYWORDS
arithmetic, error, environment, POSIX, precision,
subprocess, variables
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