[Linux Shell学习系列五]Shell编程基础-Shell变量进阶

$PARAMETER
${PARAMETER} 

#当参数名后面紧接着其他字符，必须使用{}
$ WORD=car
$ echo $WORDs

$ echo ${WORD}s
cars

#位置参数9以后的，也必须加{}
$ echo "Arguments 10 is $1"
$ echo "Arguments 10 is ${10}"

$ PARAMETER=TEMP
$ TEMP="It's indirect"

$ echo ${PARAMETER} #PARAMETER的值
TEMP

$ echo ${!PARAMETER} #扩展为参数TEMP的值
It's indirect

$ PARAMETER=tEmp
$ echo ${PARAMETER^} #首字母大写
TEmp
$ echo ${PARAMETER^^} #所有字母大写
TEMP
$ echo ${PARAMETER,} #首字母小写
tEmp
$ echo ${PARAMETER,,} #所有字母小写
temp
$ echo ${PARAMETER~} #首字母大小写转换
TEmp
$ echo ${PARAMETER~~} #所有字母大小写转换
TeMP

${!PREFIX*} #输出以字符串PREFIX开头的所有变量名，默认以空格隔开
${!PREFIX@}

#示例
$ echo ${!BASH*}
BASH BASHOPTS BASHPID BASH_ALIASES BASH_ARGC BASH_ARGV BASH_CMDS BASH_COMMAND BASH_LINENO BASH_SOURCE BASH_SUBSHELL BASH_VERSINFO BASH_VERSION

$ echo ${!BASH@}
BASH BASHOPTS BASHPID BASH_ALIASES BASH_ARGC BASH_ARGV BASH_CMDS BASH_COMMAND BASH_LINENO BASH_SOURCE BASH_SUBSHELL BASH_VERSINFO BASH_VERSION

${PARAMETER#PATTERN} #移除参数值字符中开头匹配模式的最短文本
${PARAMETER##PATTERN} #移除参数值字符中开头匹配模式的最长文本
${PARAMETER%PATTERN} #移除参数值字符中末尾匹配模式的最短文本
${PARAMETER%%PATTERN} #移除参数值字符中末尾匹配模式的最长文本

#示例：
$ MYSTRING="This is used for removing string"
$ echo ${MYSTRING}
This is used for removing string
$ echo ${MYSTRING#* }
is used for removing string
$ echo ${MYSTRING##* }
string
$ echo ${MYSTRING% *}
This is used for removing
$ echo ${MYSTRING%% *}
This

#常用场景：提取文件名的一部分
$ FILENAME=echotime.sh
$ echo ${FILENAME}
echotime.sh
$ echo ${FILENAME##*.} #提取后缀
sh
$ echo ${FILENAME%.*} #移除后缀
echotime

$ echo ${FILENAME}
/home/user/echotime.sh
$ echo ${FILENAME##*/} #提取文件名
echotime.sh
$ echo ${FILENAME%/*} #提取目录名
/home/user

${PARAMETER/PATTEN/STRING} #替换一个匹配指定模式的子字符串
${PARAMETER//PATTEN/STRING} #替换所有匹配指定模式的子字符串
${PARAMETER/PATTEN} #不指定替换的字符串，则为删除一个匹配指定模式的子字符串
${PARAMETER//PATTEN} #不指定替换的字符串，则为删除一个匹配指定模式的子字符串

$ MYSTRING="This is used for replacing string or removing string"
$ echo ${MYSTRING}
This is used for replacing string or removing string
$ echo ${MYSTRING/string/characters} #替换一个
This is used for replacing characters or removing string
$ echo ${MYSTRING//string/characters} #替换所有
This is used for replacing characters or removing characters
$ echo ${MYSTRING/string} #删除一个
This is used for replacing or removing string
$ echo ${MYSTRING//string} #删除所有
This is used for replacing or removing

${#PARAMETER}  #获取字符串的长度

$ MYSTRING="Hello World"
$ echo ${#MYSTRING}
11

${PAREMETER:OFFSET} #从指定位置截取到参数值的末尾
${PAREMETER:OFFSET:LENGTH} #从指定位置截取指定长度的字符串

$ MYSTRING="This is used for substring expansion"
$ echo ${MYSTRING}
This is used for substring expansion
$ echo ${MYSTRING:8} #未指定长度
used for substring expansion
$ echo ${MYSTRING:8:13} #指定长度
used for subs

${PAREMETER:-WORD} #如果PAREMETER是未定义或者null时，扩展WORD，否则扩展PAREMETER
${PAREMETER-WORD} #与上面不同：只有PAREMETER是未定义时，才使用WORD

$ unset MYSTRING #未定义
$ echo ${MYSTRING}

$ echo ${MYSTRING:-Hello World} #未定义
Hello World
$ echo ${MYSTRING}

$ MYSTRING="Hi"
$ echo ${MYSTRING:-Hello World} #定义
Hi

${PAREMETER:=WORD} #如果PAREMETER是未定义或者null时，扩展WORD，并将WORD赋值给PAREMETER
${PAREMETER=WORD} #与上面不同：只有PAREMETER是未定义时，才使用WORD，并将WORD赋值给PAREMETER

$ unset MYSTRING
$ echo ${MYSTRING}

$ echo ${MYSTRING:=Hello World} #未定义
Hello World
$ echo ${MYSTRING} #赋值
Hello World
$ MYSTRING="Hi"
$ echo ${MYSTRING:=Hello World} #已定义
Hi
$ echo ${MYSTRING} #不赋值
Hi

${PAREMETER:+WORD} #如果PAREMETER是未定义或者null时，不扩展任何内容；如果PAREMETER是已定义且不为空，则扩展WORD，而不是PARAMETER的值
${PAREMETER+WORD} #与上面不同：#如果PAREMETER是未定义时，不扩展任何内容；如果PAREMETER是已定义，则扩展WORD

$ unset MYSTRING
$ echo ${MYSTRING}

$ echo ${MYSTRING:+NOTE: MYSTRINT seems to be set} #未定义，不扩展任何内容

$ MYSTRING="Hi"
$ echo ${MYSTRING}
Hi
$ echo ${MYSTRING:+NOTE: MYSTRINT seems to be set} #已定义，扩展WORD而不是PARAMETER
NOTE: MYSTRINT seems to be set

${PAREMETER:?WORD} #如果PAREMETER是未定义或者null时，返回一个错误，以WORD为错误信息，否则扩展PARAMETER的值
${PAREMETER?WORD} #与上面不同：如果PAREMETER是未定义时，返回一个错误，以WORD为错误信息，否则扩展PAREMETER，为空则返回空

$ unset MYSTRING
$ echo ${MYSTRING}

$ echo ${MYSTRING:?Error: MYSTRINT is not set}
-bash: MYSTRING: Error: MYSTRINT is not set
$ MYSTRING="Hi"
$ echo ${MYSTRING:?Error: MYSTRINT is not set}
Hi