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Perl also provides three alternatealternative logical operators: {{and}}, {{or}}, and {{not}}. They have the same meanings as {{&&}}, {{||}}, and {{\!}}. They have much lower binding precedence, which makes them useful for control flow \[[Wall 2011|AA. Bibliography#Manpages]\]. They are called the late-precedence logical operators, whereas {{&&}}, {{||}}, and {{!}} are called the early-precedence logical operators.

It is possible to mix the early-precedence logical operators with the late-precedence logical operators, but this mixture of precedence will often lead leads to confusing, counterintuitive behavior. Therefore, every Perl expression should use either the early-precedence operators or the late-precedence ones, never both.

\[[Conway 2005|AA. Bibliography#Conway 2005]\] recommends avoiding the use of {{not}} and {{and}} entirely, and only using {{or}} only in control-flow operations, as a failure mode:

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This noncompliant code example checks a file to see if it is suitable for suitability as an output file. It does this by checking to see that the file does not exist.

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This code is perfectly fine. However, it is later amended to also work if the file does exist , but can be overwritten.

if (not -f $file || -w $file) {

This code will not behave as expected , because the binding rules are lower for the not operator than for the ! operator. This code will instead behave like the followinginstead behaves as follows:

if (not (-f $file || -w $file)) {

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This compliant solution uses the ! operator in conjunction with the || operator. This code has the desired behavior of determining if a file either does not exist , or does exist but is overwritable.

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This compliant solution uses the early-precedence operators consistently. Again, the code works as expected.

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