bash在变量赋值的过程中， 不做路径名扩展(pathname expansion)

# cd /home/xyz/tmp

# ls 

etc  etc.tar.bz2

# a=*

# echo $a

etc  etc.tar.bz2

# echo "$a"

*

# 

# unset a

# a="*"

# echo $a

etc  etc.tar.bz2

# echo "$a"

*

#

在bash的解析过程中， 双引号可以阻止词的拆分。 原本以为a=*， 会被扩展成a="etc etc.tar.bz2"， 但是其实在执行过程中， 并没有被扩展。

原因： man bash

name=[value]

If  value  is not given, the variable is assigned the null string.  All

values undergo tilde expansion, parameter and variable expansion,  com-

mand  substitution, arithmetic expansion, and quote removal (see EXPAN-

SION below).  If the variable has its integer attribute set, then value

is evaluated as an arithmetic expression even if the $((...)) expansion

is not used (see Arithmetic Expansion below).  Word  splitting  is  not

performed,  with the exception of "$@" as explained below under Special

Parameters.  Pathname expansion is not  performed.   Assignment state-

ments  may  also appear as  arguments to the alias, declare, typeset,

export, readonly, and local builtin commands.