shell学习之常用bash内置变量
常用的Bash内置变量1 BASH_COMMAND当前执行的命令
2 LINENO显示当前所在行号
/bin/bash
echo "this is test about ARGLINENO"
echo "line now in :$LINENO"
结果为
# ./bash.sh
this is test about ARG LINENO
line now in : 4
方便调试
3 FUNCNAME在第几层函数
#!/bin/bash
#
function test1(){
echo "test1:FUNCNAME is${FUNCNAME}"
echo "test1:FUNCNAME is${FUNCNAME}"
echo "test1:FUNCNAME is${FUNCNAME}"
test2
}
function test2(){
echo "test2:FUNCNAME is${FUNCNAME}"
echo "test2:FUNCNAME is${FUNCNAME}"
echo "test2:FUNCNAME is${FUNCNAME}"
}
test1
运行结果为
liuliancao@liuliancao-K45VD:~/shell$ ./bash1.sh
test1:FUNCNAME is test1
#此时第一层func为本函数，所以是test1
test1:FUNCNAME is main
#第二层为二层函数，应该为main，称为主脚本，调用test1的函数
test1:FUNCNAME is
#再下层就没有了，下面的同理
test2:FUNCNAME is test2
test2:FUNCNAME is test1
test2:FUNCNAME is main
#这里可以方便调试
4 HOSTNAME HOSTTYPE HOMEUIDGROUPS
这些大家应该都比较熟悉，我们看一下我的主机中它们的值
liuliancao@liuliancao-K45VD:~/shell$ echo$HOSTNAME;echo $HOSTTYPE;echo $HOME;echo $GROUPS
liuliancao-K45VD
x86_64
/home/liuliancao
1000
liuliancao@liuliancao-K45VD:~/shell$ echo $UID
1000
5 OLDPWD上个工作目录PWD 当前工作目录
liuliancao@liuliancao-K45VD:~/shell$ echo$PWD;echo $OLDPWD
/home/liuliancao/shell
/etc
6 $$ SHELL本身的PID
liuliancao@liuliancao-K45VD:~/shell$ echo $$
22535
liuliancao@liuliancao-K45VD:~/shell$ ps -e |grep bash
22535 pts/6 00:00:00 bash
7 RANDOM 随机数生成器
#random.sh
#!/bin/bash
echo "this is a random nu from 0 to 30"
scope=30
num1="`expr $RANDOM % $scope + 0`"
num2="`expr $RANDOM % $scope + 0`"
echo "nu1: ${num1}"
echo "nu2: ${num2}"
运行结果为：
liuliancao@liuliancao-K45VD:~/shell$./random.sh
this is a random nu from 0 to 30
nu1: 20
nu2: 8
liuliancao@liuliancao-K45VD:~/shell$./random.sh
this is a random nu from 0 to 30
nu1: 24
nu2: 15
#相当实用的
8 REPLY 当read没有变量名时此时，内容保存在该变量中
#reply.sh
#!/bin/bash
read -p "no arg test:"
echo "\$REPLY is$REPLY"
结果为：
liuliancao@liuliancao-K45VD:~/shell$ ./reply.sh
no arg test:hello ok
$REPLY ishello ok
#说不定什么时候用到这个变量
9 SECONDS脚本运行的时间
#seconds.sh
#!/bin/bash
sleep 2
echo "script run $SECONDS already!"
结果为
liuliancao@liuliancao-K45VD:~/shell$./seconds.sh
script run 2 already!
#可以很方便地测试脚本运行性能呢
10GLOBIGNORE对通配符忽略某些通配模式
～/shell文件夹下有如下的文件
liuliancao@liuliancao-K45VD:~/shell$ ls -al
total 24
drwxrwxr-x2 liuliancao liuliancao 40965月20 19:40 .
drwxr-xr-x 45 liuliancao liuliancao 40965月20 19:37 ..
-rw-rw-r--1 liuliancao liuliancao 05月20 19:40 1.txt
-rw-rw-r--1 liuliancao liuliancao 05月20 19:40 2.html
-rw-rw-r--1 liuliancao liuliancao 05月20 19:40 3.c
-rwxrwxr-x1 liuliancao liuliancao3245月20 19:02 bash1.sh
-rwxrwxr-x1 liuliancao liuliancao1825月20 19:28 random.sh
-rwxrwxr-x1 liuliancao liuliancao 715月20 19:36 reply.sh
-rwxrwxr-x1 liuliancao liuliancao 685月20 19:37 seconds.sh
-rw-rw-r--1 liuliancao liuliancao 05月20 19:40 .xmind
如果我们修改下
liuliancao@liuliancao-K45VD:~/shell$GLOBIGNORE=*.txt
liuliancao@liuliancao-K45VD:~/shell$ ls *
2.html3.cbash1.shrandom.shreply.sh seconds.sh.xmind
liuliancao@liuliancao-K45VD:~/shell$ rm *.txt
rm: cannot remove ‘*.txt’: No such file ordirectory
#hah，成功隐藏了文件，不过只是对通配符有关，其实我们可以用来对制定文件夹内的一些满足某种模式的进行忽略，其他的进行自己想要的操作，上面的就可以删除除了.txt的文件，修改为rm*
11 IFS (Internal Field Separator)空格分隔的内容
#ifs.sh
#!/bin/bash
#save orign IFS,and set it to :
OIFS=$IFS
IFS=":"
#next manage to read the val with separator :
read -p "input something with separator :"h1 h2 h3
echo "h1:${h1}"
echo "h2:${h2}"
echo "h3:${h3}"
#return to orign
IFS=$OIFS
运行结果为
liuliancao@liuliancao-K45VD:~/shell$ ./ifs.sh
input something with separator :liuliancao :qixue : linux
h1:liuliancao
h2: qixue
h3: linux
12 PATH 执行文件查找路径
通常命令执行前会去PATH变量按顺序查找是否有该命令，找到就执行
第一次搜索完这个命令，系统就会把命令的路径保存在hash表中，方便以后实用，实用hash-r可以清空hash表
关于PATH如果PATH开头有一个：是挺危险的，它会扩展为当前目录，此时目录下如果有一个ls命令，则可获得root的权限
13 TMOUT 用于readselect 交互式shell，为其指定超时时间
#tmout.sh
#!/bin/bash
TMOUT=3
echo "you only have 3 seconds to input "
read -p"hah,just a test:" test
echo "you entered $test"
结果为
liuliancao@liuliancao-K45VD:~/shell$ ./tmout.sh
you only have 3 seconds to input
hah,just a test:you entered
最后补充一下
SHELLOPTS的一些
对应一个命令shopt
-p 表示print显示 -u 表示停止选项 -s 表示启用选项
liuliancao@liuliancao-K45VD:~/shell$ shopt -p
shopt -u autocd
shopt -u cdable_vars#cd参数可以是变量
shopt -u cdspell#纠正拼写错误
shopt -u checkhash#执行命令先在hash表中查找
shopt -u checkjobs#
shopt -s checkwinsize#检查窗口大小，自动更新lines和column
shopt -s cmdhist#多行命令保存为一行存在history
shopt -u compat31
shopt -u compat32
shopt -u compat40
shopt -u compat41
shopt -u compat42
shopt -s complete_fullquote
shopt -u direxpand
shopt -u dirspell
shopt -u dotglob
shopt -u execfail#交互式shell不会因为exec内置命令不能执行而退出
shopt -s expand_aliases#别名被扩展
shopt -u extdebug
shopt -s extglob#打开扩展通配
shopt -s extquote
shopt -u failglob
shopt -s force_fignore
shopt -u globstar
shopt -u globasciiranges
shopt -u gnu_errfmt
shopt -shistappend#shell退出，历史清单会添加到histfile文件，而不是覆盖
shopt -u histreedit
shopt -u histverify
shopt -u hostcomplete
shopt -u huponexit
shopt -s interactive_comments#表示#开头的语句可以被忽略
shopt -u lastpipe
shopt -u lithist
shopt -u login_shell
shopt -u mailwarn
shopt -u no_empty_cmd_completion
shopt -u nocaseglob
shopt -u nocasematch
shopt -u nullglob
shopt -s progcomp
shopt -s promptvars
shopt -u restricted_shell
shopt -u shift_verbose
shopt -ssourcepath#如果设置，source内置命令使用PATH的值来寻找参数
shopt -u xpg_echo
总结其实bash内置变量表面上看来挺枯燥，其实还是挺有意思，需要自己去体会哦。
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