Clear

Clear[s1,s2,…]

clears values and definitions for the symbols si.

Clear[patt1,patt2,…]

clears values and definitions for all symbols whose names textually match any of the arbitrary string patterns patti.

Clear[{spec1,spec2,…}]

clears values and definitions for any symbols that are equal to or whose names match any of the speci.

Details

  • Clear does not clear attributes, defaults, options or messages associated with symbols. »
  • The pattern patt can be given as a string with metacharacters, as StringExpression[…] or as RegularExpression["regex"]. »
  • Clear allows abbreviated string patterns containing the following metacharacters:
  • *zero or more characters
    @one or more characters, excluding uppercase letters
  • Clear["context`*"] clears all symbols in a particular context. »
  • Clear["`*"] clears all symbols in the current context. »
  • Clear does not affect symbols with the attribute Protected. »
  • Clear has attribute HoldAll. »

Examples

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Basic Examples  (2)

Clear a variable:

The variable no longer has a value:

Define values for a symbol:

Clear values:

Scope  (12)

Symbol Inputs  (7)

Clear values of variables (ownvalues):

Clear functions (downvalues):

Clear upvalues:

Clear subvalues:

Clear formatting:

Clear several symbols:

Use a combination of symbols and symbol names:

Only x3 remains defined:

Using Patterns  (5)

Specify symbols to clear as string patterns:

Clear all symbols in the current context:

Clear all symbols in a given context:

Clear all 2-character symbols in the current context using StringExpression:

The symbols x1 and x2 were cleared, but y remains unaffected:

Clear all 3-character symbols in the current context using RegularExpression:

Applications  (2)

Clear any old definitions before making new ones:

Unprotect and clear all symbols in a package, to allow it to be read twice:

Properties & Relations  (6)

Clear[pattern] clears the same symbols as Clear/@Names[pattern]:

Use Unset (=.) to clear definitions with a particular left-hand side:

Clear all definitions:

Clear does not remove attributes, defaults or options:

Use ClearAll to clear everything:

Clear does not remove messages:

Use ClearAll to clear messages:

Clear removes all definitions but leaves the symbol intact:

Remove removes the symbol completely:

Clear has the attribute HoldAll:

This clears symbol itself:

This clears its value:

Possible Issues  (2)

Protected symbols cannot be cleared:

Use Unprotect to clear definitions of protected symbols:

When using a pattern without a context mark, all matching symbols on $ContextPath are cleared:

The symbol xy was cleared, along with attempts to clear several system symbols:

Use a pattern with an explicit context mark to avoid potentially matching symbols from system or other contexts:

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