BASH_VERSINFO[3]
The build version.
BASH_VERSINFO[4]
The release status (e.g., beta1).
BASH_VERSINFO[5]
The value of MACHTYPE.
BASH_VERSION
The version number of the current instance of Bash.
BASH_XTRACEFD
If set to an integer corresponding to a valid file descriptor, Bash will write the trace output generated when ‘set -x’ is enabled to that file descriptor. This allows tracing output to be separated from diagnostic and error messages. The file descriptor is closed when BASH_XTRACEFD is unset or assigned a new value.
Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to the standard error. Note that setting BASH_XTRACEFD to
2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed.
CHILD_MAX
Set the number of exited child status values for the shell to remember. Bash will not allow this value to be decreased below a posix-mandated minimum, and there is a maximum value (currently 8192) that this may not exceed. The minimum value is system-dependent.
COLUMNS
Used by the select command to determine the terminal width when printing selection lists. Automatically set if the checkwinsize option is enabled (see
Section 4.3.2 [The Shopt Builtin], page 62), or in an interactive shell upon receipt of a SIGWINCH.
COMP_CWORD
An index into ${COMP_WORDS} of the word containing the current cursor po- sition. This variable is available only in shell functions invoked by the pro- grammable completion facilities (see Section 8.6 [Programmable Completion], page 124).
COMP_LINE
The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see
Section 8.6 [Programmable Completion], page 124).
COMP_POINT
The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current command, the value of this variable is equal to ${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Section 8.6 [Programmable Completion], page 124).