bash:意外的数组成员句柄

Question

我在最后一个命令行中发现了以下bash行为.对我来说,这完全出乎意料.

$ set | grep ^BASH_VERSINFO             # Show the array
BASH_VERSINFO=([0]="3" [1]="2" [2]="25" [3]="1" [4]="release" [5]="x86_64-redhat-linux-gnu")

$ echo "${BASH_VERSINFO[@]}"             # Print all array
3 2 25 1 release x86_64-redhat-linux-gnu

$ echo "${BASH_VERSINFO[@]%e}"           # Print all array removing final 'e' of every member
3 2 25 1 releas x86_64-redhat-linux-gnu

$ i=4; echo "${BASH_VERSINFO[i]}"        # Print an array member
release
$ i=4; echo "${BASH_VERSINFO[i++]}"      # Print an array member and increase the 'i' variable
release
$ i=4; echo "${BASH_VERSINFO[i]%e}"      # Print an array member removing the final 'e'
releas
$ i=4; echo "${BASH_VERSINFO[i++]%e}"    # Why does bash use the next member?
x86_64-redhat-linux-gnu

似乎bash预先增加'i'变量.

类似的奇怪行为:

$ i=5; echo "${BASH_VERSINFO[--i]}"    # Print array member ${BASH_VERSINFO[4]}. 'i' is descreased one time.
release
$ i=5; echo "${BASH_VERSINFO[--i]%e}"  # Print array member ${BASH_VERSINFO[3]%e}. 'i' is descreased two times.
1

有谁能告诉我这种行为？

Thanx提前

Answer 1

这似乎是一个已修复的错误,可能是这个:

(来自bashChangeLog - bash-4.2-alpha和bash-4.1-release之间的变化)

修复了算术扩展中的一个错误,该错误导致在某些情况下对数组扩展中的索引进行两次求值.

WORKSFORME:

$ echo "${BASH_VERSINFO[*]}"
4 2 42 1 release i586-pc-linux-gnu
$ i=4; echo "${BASH_VERSINFO[i++]}"; echo "$i"
release
5
$ i=4; echo "${BASH_VERSINFO[i++]%e}"; echo "$i"
releas
5