${!VARIABLE}这种结构是什么意思，实在是查不到啊

jqq850226

BLFS中 /etc/profile 的代码：

cat > /etc/profile << "EOF"
# Begin /etc/profile
# Written for Beyond Linux From Scratch
# by James Robertson <jameswrobertson@earthlink.net>
# modifications by Dagmar d'Surreal <rivyqntzne@pbzpnfg.arg>

# System wide environment variables and startup programs.

# System wide aliases and functions should go in /etc/bashrc.  Personal
# environment variables and startup programs should go into
# ~/.bash_profile.  Personal aliases and functions should go into
# ~/.bashrc.

# Functions to help us manage paths.  Second argument is the name of the
# path variable to be modified (default: PATH)
pathremove () {
        local IFS=':'
        local NEWPATH
        local DIR
        local PATHVARIABLE=${2:-PATH}
        for DIR in ${!PATHVARIABLE} ; do
                if [ "$DIR" != "$1" ] ; then
                  NEWPATH=${NEWPATH:+$NEWPATH:}$DIR
                fi
        done
        export $PATHVARIABLE="$NEWPATH"
}

pathprepend () {
        pathremove $1 $2
        local PATHVARIABLE=${2:-PATH}
        export $PATHVARIABLE="$1${!PATHVARIABLE:+{!PATHVARIABLE}}"
}

pathappend () {
        pathremove $1 $2
        local PATHVARIABLE=${2:-PATH}
        export $PATHVARIABLE="${!PATHVARIABLE:+${!PATHVARIABLE}:}$1"
}


# Set the initial path
export PATH=/bin:/usr/bin

if [ $EUID -eq 0 ] ; then
        pathappend /sbin:/usr/sbin
        unset HISTFILE
fi

# Setup some environment variables.
export HISTSIZE=1000
export HISTIGNORE="&:[bf]g:exit"
#export PS1="[\u@\h \w]\\$ "
export PS1='\u@\h:\w\$ '

for script in /etc/profile.d/*.sh ; do
        if [ -r $script ] ; then
                . $script
        fi
done

# Now to clean up
unset pathremove pathprepend pathappend

# End /etc/profile
EOF

biinn

man bash, then search for 'Parameter Expansion'.

jqq850226

手册中只有这两种：
${!prefix*}
${!prefix@}
   Expands to the names of variables whose names begin with prefix, separated by the first character of the IFS special variable.

${!name[@]}
${!name

}
  If name is an array variable,  expands  to  the  list  of  array indices  (keys)  assigned  in  name.   If  name is not an array, expands to 0 if name is set and null otherwise.  When @ is  used and the expansion appears within double quotes, each key expands to a separate word.

可是这句：
export ATHVARIABLE="$1${!PATHVARIABLE:+{!PATHVARIABLE}}"
里面没有“@”与“*”符号，又怎么解释？

feiliang1983

好像是bash2的用法？http://www.linuxsir.cn/main/doc/ ... bash2.html#BASH2REF

sltk

这个是间接引用，像指针（当然不是）

try: a=b b=c echo ${!a}