system/zsh
system/zsh
1
0
Fork 0
mirror of https://github.com/zsh-users/zsh synced 2024-07-03 08:08:39 +00:00
Code Issues Projects Releases Wiki Activity

users/29882: Explain $RANDOM predictability

Browse Source
This commit is contained in:
Bart Schaefer 2024-05-24 19:27:14 -07:00
parent 300ce96080
commit 9dcaf78997
2 changed files with 34 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
ChangeLog
View File

@ -1,5 +1,7 @@
2024-05-24 Bart Schaefer <schaefer@zsh.org> 2024-05-24 Bart Schaefer <schaefer@zsh.org>
* users/29882: Etc/FAQ.yo: Explain $RANDOM predictability
* 52910: Functions/Misc/zmv: Improve handling of **/ patterns * 52910: Functions/Misc/zmv: Improve handling of **/ patterns
* 52904: Completion/Unix/Command/_git: Improve quoting of paths * 52904: Completion/Unix/Command/_git: Improve quoting of paths

32
Etc/FAQ.yo
View File

@ -137,6 +137,7 @@ Chapter 3: How to get various things to work
3.28. How do I edit the input buffer in $EDITOR? 3.28. How do I edit the input buffer in $EDITOR?
3.29. Why does `which' output for missing commands go to stdout? 3.29. Why does `which' output for missing commands go to stdout?
3.30. Why doesn't the expansion mytt(*.{tex,aux,pdf}) do what I expect? 3.30. Why doesn't the expansion mytt(*.{tex,aux,pdf}) do what I expect?
3.31. Why does mytt($RANDOM) return the same number more than once?
Chapter 4: The mysteries of completion Chapter 4: The mysteries of completion
4.1. What is 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 This is harder for the user to remember but easier for the shell to
parse! 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) chapter(The mysteries of completion)
sect(What is completion?) sect(What is completion?)