$BatchInput (Built-in Mathematica Symbol)

$BatchInput is True if input in the current session is being fed directly to the Mathematica kernel in batch mode.

$CurrentLink (Built-in Mathematica Symbol)

$CurrentLink is the LinkObject representing the MathLink connection for an external program currently being installed or being called.

$ImportFormats (Built-in Mathematica Symbol)

$ImportFormats gives a list of import formats currently supported in your Mathematica system.

$MaxMachineNumber (Built-in Mathematica Symbol)

$MaxMachineNumber is the largest machine-precision number that can be used on a particular computer system.

$MaxNumber (Built-in Mathematica Symbol)

$MaxNumber gives the maximum arbitrary-precision number that can be represented on a particular computer system.

$MaxPrecision (Built-in Mathematica Symbol)

$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.

$MessageList (Built-in Mathematica Symbol)

$MessageList is a global variable that gives a list of the names of messages generated during the evaluation of the current input line.

$Path (Built-in Mathematica Symbol)

$Path gives the default list of directories to search in attempting to find an external file.

$PrePrint (Built-in Mathematica Symbol)

$PrePrint is a global variable whose value, if set, is applied to every expression before it is printed.

$PreRead (Built-in Mathematica Symbol)

$PreRead is a global variable whose value, if set, is applied to the text or box form of every input expression before it is fed to Mathematica.