shell中的特殊字符

shell中的特殊字符

注释’#’

[root@localhost ~]# #hello world
[root@localhost ~]#     #hello world
[root@localhost ~]# echo hello #world
hello
[root@localhost ~]# echo "hello #world"
hello #world

变量取值’$’

[root@localhost ~]# A=11
[root@localhost ~]# AB=22
[root@localhost ~]# echo $A
11
[root@localhost ~]# echo $AB
22
[root@localhost ~]# echo ${A}B
11B

参数取值’$’

[root@localhost ~]# cat var.sh
#!/bin/bash
echo $0  ## program name
echo $1  ## the first parameter
echo $2
echo $3
echo $4
echo $5
echo $6
echo $7
echo $8
echo $9
echo $#  ## parameter number
echo $*  ## string
echo $@  ## string array
[root@localhost ~]# ./var.sh 111 222 333 444 555 666 777 888 999
./var.sh
111
222
333
444
555
666
777
888
999
9
111 222 333 444 555 666 777 888 999
111 222 333 444 555 666 777 888 999

返回值’$?’

[root@localhost ~]# ls xxx
ls: cannot access xxx: No such file or directory
[root@localhost ~]# echo $?
2
[root@localhost ~]# ls
anaconda-ks.cfg  install.log  install.log.syslog
[root@localhost ~]# echo $?
0

执行最近命令’!’

[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# !!
echo 111
111
[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# !-1
echo 111
111
[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# !-2
echo 222
222
[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# !-3
echo 333
333

执行历史列表中的命令’!’

[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# history | tail -4
1083  echo 333
1084  echo 222
1085  echo 111
1086  history | tail -4
[root@localhost ~]# !1084
echo 222
222

执行最近相似命令

[root@localhost ~]# echo 333
333
[root@localhost ~]# ls
anaconda-ks.cfg  install.log  install.log.syslog  temp  var.sh
[root@localhost ~]# !echo
echo 333
333
4000

[root@localhost ~]# echo 333
333
[root@localhost ~]# echo 222
222
[root@localhost ~]# echo 111
111
[root@localhost ~]# !?222
echo 222
222
[root@localhost ~]#