Strings: Single Quote Vs Double Quotes

In UNIX Shell

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Double Quotes : In (Most ) UNIX shells and other scripting languages like perl, the interpreter would parse through the string inorder to perform substitutions for any variables in the string.

Single Quotes: Interpreter leaves the string alone. It is treated as a string literal.

In C

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Double Quotes: For strings

Single Quotes : For single character literals.

e.g

char c[];

c = 'c'; ==> SINGLE Quotes

c = "char"; ==> DOUBLE quotes