bash-4.4 here string 处理的变化(or bug?)

yjh777

1. '''
   
2. [yjh@bash4.4 ~]$ LANG=C bash --version|head -n1
   
3. GNU bash, version 4.4.12(1)-release (x86_64-redhat-linux-gnu)
   
4. [yjh@bash4.4 ~]$ read a <<<$(echo -e "foo\t\tbar"); echo "$a"
   
5. foo        bar
   
6. '''

复制代码

1. '''
   
2. [yjh@bash4.2 ~]$ bash --version|head -n1
   
3. GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)
   
4. [yjh@bash4.2 ~]$ read a <<<$(echo -e "foo\t\tbar"); echo "$a"
   
5. foo bar
   
6. '''

复制代码

1. 
   
2. '''
   
3. [root@bash-3.2 ~]# bash --version
   
4. GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)
   
5. Copyright (C) 2005 Free Software Foundation, Inc.
   
6. [root@bash-3.2 ~]# read a <<<$(echo -e "foo\t\tbar"); echo "$a"
   
7. foo bar
   
8. '''

复制代码

1. '''
   
2. [root@bash-4.1 ~]# bash --version
   
3. GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
   
4. Copyright (C) 2009 Free Software Foundation, Inc.
   
5. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
   
6. 
   
7. This is free software; you are free to change and redistribute it.
   
8. There is NO WARRANTY, to the extent permitted by law.
   
9. [root@bash-4.1 ~]# read a <<<$(echo -e "foo\t\tbar"); echo "$a"
   
10. foo bar
    
11. '''

复制代码

yinyuemi

回复 1# yjh777

和<<<好像没有关系，echo "$a" 和 echo $a 的区别

yjh777

yinyuemi 发表于 2017-11-22 17:14
回复 1# yjh777

和

你好好看看，实测一下再说

yjh777

bash-4.4 上 <<<  右面的所有内容，都不会通过 IFS 切割了

<<<$var  跟以前的  <<<"var"  一个效果

wh7211

回复 1# yjh777


不同shell版本之间存在差异也正常，zsh 4.3.11上测试结果和bash 4.4.12一样，为了兼容不同版本的shell，给变量赋值时最好采用赋值语句：
a="$(echo -e "foo\t\tbar")"&&echo "$a"
如果一定要用hear string，也加上双引号吧：
read a <<< "$(echo -e "foo\t\tbar")"&&echo "$a"

yinyuemi

回复 1# yjh777

找到了：
This document details the changes between this version, bash-4.4-beta, and
the previous version, bash-4.4-alpha.

1.  Changes to Bash

a.  Fixed two bugs that caused out-of-bounds reads when skipping over assignment
    statements while finding the word on which to perform programmable
    completion.

b.  Fixed a memory leak in programmable completion.

c.  Fixed a bug that could cause the shell to crash when interrupting the
    wait builtin.

d.  Fixed a bug that caused ${!vvv@} to be interpreted as introducing the new
    `@' operator.

e.  Fixed a bug that caused the && and || operators to be incorrectly optimized.

f.  The shell now undoes redirections before exiting the shell when the `-e'
    option is enabled, and a shell function fails.

g.  History expansion now skips over the history expansion character in command
    and process substitution.

h.  Fixed a bug that caused stray '\001' characters to be added to the output
    of `declare -p'.

i.  Fixed a memory leak when processing declare commands that perform compound
    array assignments.

j.  Fixed a bug that could cause the shell to crash when reading input from a
    file and the limit on open file descriptors is high.

k.  Fixed a bug that caused the ERR and RETURN traps to be unset if they were
    set in a shell function but unset previously.

l.  Fixed a bug that caused several signals to be ignored if `exec' failed in
    an interactive shell.

m.  A posix-mode non-interactive shell now considers a parameter expansion error
    to be a fatal error.

n.  The `time' command now prints timing statistics for failed commands when
    the -e option is enabled.

o.  Fixed a bug that caused the shell to crash when attempting to indirectly
    expand a shell variable with an invalid name.

p.  Fixed a bug that caused the shell to crash when running a trap containing
    a process substitution.

q.  Bash now prints the keyword `function' before a function with the same name
    as a reserved word when using `declare -f' to avoid parse errors when
    reusing the output as input.

r.  Fixed a bug that caused the shell to crash when using declare -g to attempt
    to redefine an existing global indexed array variable as an associative
    array.

s.  Fixed a memory leak that occurred when interrupting brace expansions
    generating a sequence.

t.  Fixed a bug that resulted in alias expansion in redirections.

u.  The `declare -a' and `declare -A' commands now print fewer warnings when
    attempting to create and initialize an array at the same time, but
    relying on word expansions to construct the compound assignment.

v.  The `help' builtin now behaves better in locales where each wide
    character occupies more than one display column.

w.  The `read' builtin no longer has a possible race condition when a timeout
    occurs.

x.  Fixed several expansion problems encountered when IFS="'".

y.  Fixed a problem with the expansion of $'\c?'.

z.  Bash no longer splits the expansion of here-strings, as the documentation
    has always said.

aa. Bash now puts `s' in the value of $- if the shell is reading from standard
    input, as Posix requires.

bb. Fixed a bug that caused the shell to crash if invoked with a NULL
    environment.

cc. The shell now only trusts an inherited value for $PWD if it begins with a
    `/'.

dd. Fixed a memory leak when creating local array variables and assigning to
    them using compound assignment with the `declare' builtin.

ee. Fixed a bug that could cause the shell to crash when processing nested here
    documents inside a command substitution.

ff. Array keys and values are now displayed using $'...' quoting where
    appropriate.

gg. Fixed a bug that could cause the shell to crash if the replacement string
    in pattern substitution was NULL.

hh. Fixed a bug that could cause the shell to crash if a command substitution
    contained a non-fatal syntax error.

ii. Fixed a bug that could cause the shell to crash if variable indirection
    resulted in a NULL variable.

jj. Fixed a bug that could cause the shell to crash if a long string contained
    multiple unterminated parameter expansion constructs.

kk. Improved the code that acts on SIGINT received while waiting for a child
    process only if the child exits due to SIGINT.

ll. $BASH_SUBSHELL now has more consistent values in asynchronous simple
    commands.

yjh777

回复 6# yinyuemi

赞！我刚开始只搜了 here string ，没想到它用的是 here-string；

问了一下开发，说是以前的处理算bug. current behavior matches the behavior of ksh and zsh ;

ziyunfei

Here String 中不该进行分词 www.cnblogs.com/ziyunfei/p/4781553.html

yjh777

ziyunfei 发表于 2017-12-04 15:16
Here String 中不该进行分词 www.cnblogs.com/ziyunfei/p/4781553.html

嗯，知道了。

下次发现这种问题最好直接report到上游去，像这样(如果只写在自己博客里,被看到和修复的可能性太小了):
  http://lists.gnu.org/archive/html/bug-bash/2015-09/msg00022.html
  http://lists.gnu.org/archive/html/bug-bash/2017-11/msg00104.html

  http://lists.gnu.org/archive/html/bug-bash/2017-11/msg00118.html
  http://lists.gnu.org/archive/htm ... /threads.html#00099