bash – 具有相同名称的本地只读与全局只读变量的函数

发布时间：2020-12-15 18:36:58 所属栏目：安全来源：网络整理

导读：当我有一个函数本地只读变量和具有相同名称的全局只读变量时,我会得到一个惊人的行为. 当从全局声明中删除只读选项时.即 declare -r var="main" 改为： declare var="main" 我得到了预期的行为.我一直在阅读bash手册页,但我找不到这个行为的解释.你能请我指

当我有一个函数本地只读变量和具有相同名称的全局只读变量时,我会得到一个惊人的行为.

当从全局声明中删除只读选项时.即

declare -r var="main"

改为：

declare var="main"

我得到了预期的行为.我一直在阅读bash手册页,但我找不到这个行为的解释.你能请我指出手册中解释这个问题的部分吗？

我认为这是一个类似的问题,比How does lexical scoping supported in different shell languages?更具体.

细节：

$cat readonly_variable.sh 
#!/bin/bash

# expected output:
#
# BASH_VERSION = 3.2.25(1)-release
# function
# main
#
# but instead getting:
#
# BASH_VERSION = 3.2.25(1)-release
# ./readonly_variable.sh: line 6: local: var: readonly variable
# main
# main
#
# when read-only option (-r) is removed from global declaration (*),the output
# is expected

set -o nounset

function func {
  local -r var="function"
  echo "$var"
}

declare -r var="main" # (*)

echo BASH_VERSION = $BASH_VERSION
echo $(func)
echo $var

exit 0

我陷入了这个特殊的Bash版本.

$./readonly_variable.sh
BASH_VERSION = 3.2.25(1)-release
./readonly_variable.sh: line 24: local: var: readonly variable
main
main
$

实际上,为了安全起见,明确地禁止只读全局变量的本地副本,如bash源代码(在variables.c：make_local_variable中)所示：

The test against old_var’s context level is to disallow local copies of readonly global variables (since “I” believe that this could be a security hole).

(其中“我”不是我,我只是引用)

/* Since this is called only from the local/declare/typeset code,we can
   call builtin_error here without worry (of course,it will also work
   for anything that sets this_command_name).  Variables with the `noassign'
   attribute may not be made local.  The test against old_var's context
   level is to disallow local copies of readonly global variables (since I
   believe that this could be a security hole).  Readonly copies of calling
   function local variables are OK. */
if (old_var && (noassign_p (old_var) ||
   (readonly_p (old_var) && old_var->context == 0)))
{
  if (readonly_p (old_var))
    sh_readonly (name);
  return ((SHELL_VAR *)NULL);
}

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!