bash中一切变量都是以字符串的形式存储,env命令可以查看与此终端进程相关的环境变量。

man bash

查看一个进程的环境变量

1.获得程序的PID,例如Java
# pgrep java
23492

2.查看对应的环境变量
# cat /proc/23492/environ
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alt="" />

3.将输出格式化,这样查看会比上图清晰
# cat /proc/23492/environ |tr '\0' '\n'
“^@”将变换成换行符
aaarticlea/png;base64,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" alt="" />

变量赋值
var=varlue,如果value不包含空白字符,则不必加单引号或者双引号
var = value 是相等操作,注意区分,很多人这个地方发生混淆

输出变量
echo $var 或者 echo ${var}
例如:

# var=apple
# echo "${var}(s)"
apple(s)

变量字符串的常用操作

[root@Director ~]# var="hello world"

[root@Director ~]# echo ${#var}                         #计算字符串的长度,类似于"wc -m"-1;expr length "$var"

[root@Director ~]# echo ${var:}                        #从第二个字符串之后开始取,不包括第二个字符串。
llo world [root@Director ~]# echo ${var::} #从第二个字符串之后开始取,取两个字符,相当于"echo $var|cut -c 3-4"
ll [root@Director ~]# echo ${var#hell} #字符串开头删除最短匹配的字符
o world [root@Director ~]# echo ${var%ld} #从结尾开始删除最短匹配的字符
hello wor [root@Director ~]# echo ${var/world/linux} #替换匹配字符,类似 “echo ${var}|sed 's/world/linux/'”
hello linux [root@Director ~]# echo ${var/#hello/linux} #前缀匹配,则替换
linux world [root@Director ~]# echo ${var/%world/linux} #后缀匹配,则替换
hello linux [root@Director test]# echo $gender [root@Director test]# echo ${gender:-female} #变量未赋值,则定义一个值
female [root@Director test]# echo $gender [root@Director test]# echo ${gender:=female}       #变量未赋值,则定义一个值,并传递给它 
female [root@Director test]# echo $gender
female [root@Director test]# echo ${gender-male}        #变量未定义,则给予定义,若定义了则取原来的值
male

应用场景:

1.防止$path未定义,而删除了根目录或者root目录

[root@Director /]# find  ${path:=/test} -name "*.bak"|xargs rm -rf  

2.打印出文件或目录的后缀

[root@Director test]# jarName=app_20160807.jar
[root@Director test]# echo ${jarName:((${#jarName}-))}
jar

特殊变量

$PS1         系统默认:PS1="[\u@\h \W]\$"
$UID    为0时代表root用户

$TMOUT    终端timeout时间

$0,$* ,$@ , $#

[root@Director sbin]# cat /usr/local/sbin/test.sh
#!/bin/bash
echo '$0=' $0 #脚本的名称
echo '$1=' $1 #运行脚本的第n个参数
echo '$#=' $#     #运行脚本参数的个数
echo '$*=' $*     #所有参数当成单个字符串,很少使用
echo '$@=' $@     #所有参数
basename $0       #获取文件名
dirname $0       #获取文件的目录
[root@Director sbin]# sh /usr/local/sbin/test.sh aa bb
$= /usr/local/sbin/test.sh
$= aa
$#=
$*= aa bb
$@= aa bb
test.sh
/usr/local/sbin

 进程状态变量

 $?  获取执行上一个命令的返回值(0为成功,其它为失败)

$$ 获取当前shell的PID

$_ 获取之前命令或脚本的最后一个参数

!$ 执行上一个命令  

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