6 Matching Annotations
  1. Apr 2021
  2. trailblazer.to trailblazer.to
    Trailblazer
    1
    1. TylerRick 06 Apr 2021
      A falsey return value from #validate will deviate the flow and go straight to End.fail_fast.

      Similar to: How, in Rails, aborting a before_action causes all later ones to be skipped.

      short-circuit evaluation analogy
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    trailblazer.to/2.1/docs/activity.html
  3. Nov 2020
  4. wresch.github.io wresch.github.io
    Short circuit evaluation of conditionals in bash
    1
    1. TylerRick 13 Nov 2020
      Important caveat: in the combined expression, if the middle command has a non-zero exit status, then both the middle and the rightmost command end up getting executed.

      I don't think that is surprising, is it? Since && and || have the same order of precedence. So I think this is more of a clarification than a caveat.

      I think this is just because:

      a && b || c is equivalent to: (a && b) || c (so of course c gets evaluated if (a && b) is false (that if either a or b is false).

      I think they just mean, in this case:

      bedmap && mv || fail

      if mv fails, then fail still gets executed.

      Easier to see with a simpler example:

      ⟫ true && false || echo 'fail'
fail

⟫ false && true || echo 'fail'
fail

      Better example/explanation here: https://hyp.is/-foxmCVXEeuhnLM-le_R4w/mywiki.wooledge.org/BashPitfalls

      The caveat/mistake here is if you treat it / think that it is equivalent to if a then b else c. That is not the case if b has any chance of failing.

      caveat short-circuit evaluation grouping (logical expressions) order of operations (operator precedence) unclear
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    wresch.github.io/2014/04/24/bash-short-circuit-evaluation.html
  5. redsymbol.net redsymbol.net
    Use the Unofficial Bash Strict Mode (Unless You Looove Debugging)
    2
    1. TylerRick 13 Nov 2020
      The potential problem: if second_task fails, third_task will not run, and execution will continue to the next line of code - next_task, in this example. This may be exactly the behavior you want. Alternatively, you may be intending that if second_task fails, the script should immediately exit with its error code. In this case, the best choice is to use a block - i.e., curly braces: first_task && { second_task third_task } next_task Because we are using the -e option, if second_task fails, the script immediately exits.
      caveat shell scripting short-circuit evaluation grouping (logical expressions)
    2. TylerRick 13 Nov 2020
      When people write COND && COMMAND, typically they mean "if COND succeeds (or is boolean true), then execute COMMAND. Regardless, proceed to the next line of the script." It's a very convenient shorthand for a full "if/then/fi" clause.
      shorthand concise shell scripting short-circuit evaluation
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    redsymbol.net/articles/unofficial-bash-strict-mode/
  6. May 2020
  7. en.wikipedia.org en.wikipedia.org
    Short-circuit evaluation - Wikipedia
    2
    1. TylerRick 28 May 2020
      For instance, cor does not distribute over cand: compare (A cand B) cor C with (A cor C) cand (B cor C); in the case ¬A ∧ C , the second expression requires B to be defined, the first one does not
      logic short-circuit evaluation differences caveat
    2. TylerRick 28 May 2020
      short-circuit evaluation
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    en.wikipedia.org/wiki/Short-circuit_evaluation