How to Clear variables represented as a list of strings?

According to the documentation of Clear or ClearAll it is possible to provide symbols in form of regular expression (limited), in particular as string with exact symbol name.

Clear @@ {"width", "long", "line", "distance"}

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Let's say there is no possibility to do that, one way would be:

Map[Clear, 
    ToExpression[{"width", "long", "line", "distance"}, InputForm, Hold], 
    {2}]; // ReleaseHold

As Kuba notes you can use strings in Clear directly. However having an understanding of how to work with such problems is helpful so here are some other ways.

A flexible approach is to use MakeExpression to convert strings to expressions in held form (HoldComplete specifically):

MakeExpression[fullpara]

{HoldComplete[width], HoldComplete[long], HoldComplete[line], HoldComplete[distance]}

You can use Apply Join to put these in a single HoldComplete head and then Apply Clear or ClearAll:

Join @@ MakeExpression[fullpara]

HoldComplete[width, long, line, distance]

Clear @@ Join @@ MakeExpression[fullpara]  (* clears Symbols *)

A more specific approach is to use the third argument of ToExpression to Clear individual Symbols directly:

ToExpression[fullpara, StandardForm, Clear]; (* clears Symbols *)