AwkChannelWiki: logical operator

In awk, *logical operators* are used to perform [[boolean?]] operations, and a return a value of [true] or [false], depending on the values of the [operand]s.

Operator	Symbol	Description
[[and?]]	[[doubleampersand_&&?]]	Returns [true] if both [[operand?]]s are [[true?]], otherwise returns [[false?]]
[[or?]]	[[doublepipe?]]	Returns [[true?]] if either or both [[operand?]]s are [[true?]], otherwise returns [[false?]]
[[not?]]	[[pling !]]	Returns [[false] if [[operand?]] is [[true?]], otherwise returns [[true?]]

Traditionally, awk does not provide a logical [[xor?]] operator

Results of Logical Operations

[[Results_of_Logical_Operations?]]

The [[logical?]] operators return a [[boolean?]] value of 0 for [[false?]], and 1 for [[true?]]. In awk, the null strings "" are treated as [[false?]] expressions, a non null string is true:

 print (0 && 0)                 # 0 (false)
 print (0 && 7)                 # 0 (false)
 print (7 && 0)                 # 0 (false)
 print (7 && 2)                 # 1 (true)
 print (2 && 7)                 # 1 (true)
 print ("" && "")               # 0 (null strings are treated as false)
 print ("apples" && "pears")    # 1 (true)

 print (0 || 7)                 # 1 (true)
 print (7 || 0)                 # 1 (true)
 print (7 || 2)                 # 1 (true)
 print (2 || 7)                 # 1 (true)
 print ("" || "")               # 0  (null strings are treated as false)
 print ("apples" || "pears")    # 1 (true)

Precedence

[[Precedence_of_logical_operators?]]

The unary [[NOT?]] operator has a higher precedence than the dyadic [[AND?]] and [[OR?]] operators:

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Associativity

The [[dyadic?]] logical operators have left [[associativity?]], which means that the left hand [[operand?]] is evaluated before the right hand [[operand?]].