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| -rw-r--r-- | ChangeLog | 2 | ||||
| -rw-r--r-- | Etc/FAQ.yo | 32 |
2 files changed, 34 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog index 7f3412f8e..bbd1c99be 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,7 @@ 2024-05-24 Bart Schaefer <schaefer@zsh.org> + * users/29882: Etc/FAQ.yo: Explain $RANDOM predictability + * 52910: Functions/Misc/zmv: Improve handling of **/ patterns * 52904: Completion/Unix/Command/_git: Improve quoting of paths diff --git a/Etc/FAQ.yo b/Etc/FAQ.yo index 4e11637ea..2c83fe7fa 100644 --- a/Etc/FAQ.yo +++ b/Etc/FAQ.yo @@ -137,6 +137,7 @@ Chapter 3: How to get various things to work 3.28. How do I edit the input buffer in $EDITOR? 3.29. Why does `which' output for missing commands go to stdout? 3.30. Why doesn't the expansion mytt(*.{tex,aux,pdf}) do what I expect? +3.31. Why does mytt($RANDOM) return the same number more than once? Chapter 4: The mysteries of completion 4.1. What is completion? @@ -2219,6 +2220,37 @@ sect(Why doesn't the expansion mytt(*.{tex,aux,pdf}) do what I expect?) This is harder for the user to remember but easier for the shell to parse! +sect(Why does mytt($RANDOM) return the same number more than once?) + + As tt(zshparam(1)) says: + verb( + The values of RANDOM form an intentionally-repeatable + pseudo-random sequence; subshells that reference RANDOM + will result in identical pseudo-random values unless the + value of RANDOM is referenced or seeded in the parent shell + in between subshell invocations. + ) + + You can use a function, including an anonymous function, to always + evaluate mytt($RANDOM) in the parent shell. This example illustrates + the difference: + verb( + for i in {1..10}; do + echo subshell: $(echo $RANDOM) $RANDOM + () { echo parent: $(echo $1) $2 } $RANDOM $RANDOM; + done + ) + + Remember that for a pipe like mytt(A | B), zsh runs A in a subshell + and B in the current shell. This means that, for example: + verb( + for i in {1..10}; do + echo $RANDOM | tee + done + ) + also repeats the same value, because mytt($RANDOM) is evaluated in + the subshell and the parent sequence is left unchanged. + chapter(The mysteries of completion) sect(What is completion?) |