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Mathematica > Systems Interfaces & Deployment > Mathematica Sessions > Session Customization >

Built-in Mathematica Symbol

$PreRead

$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.

$PreRead is always applied to each complete input string that will be fed to Mathematica.

In multiline input with a text-based interface, whenever each line is terminated, $PreRead is typically applied to the input so far.

By default, $PreRead is not defined, meaning input strings are sent directly to evaluation:

Use "hf" as an alias for HoldForm:

Restore $PreRead to its default value:

Have Mathematica print the FullForm of parsed input expressions before evaluation:

Restore $PreRead to its default value:

By default, $PreRead is not defined, meaning input strings are sent directly to evaluation:

Use "hf" as an alias for HoldForm:

Out[3]//FullForm=

Restore $PreRead to its default value:

Have Mathematica print the FullForm of parsed input expressions before evaluation:

Out[2]=

Out[3]=

Restore $PreRead to its default value: