http://blog.csdn.net/hainan16/article/category/861739
if 语句格式
| if 条件 then Command else Command fi 别忘了这个结尾 |
| If语句忘了结尾fi test.sh: line 14: syntax error: unexpected end of fi |
if 的三种条件表达式
| if command then if 函数 then | 命令执行成功，等于返回0 （比如grep ,找到匹配） 执行失败，返回非0 （grep,没找到匹配） |
| if [ expression_r_r_r ] then | 表达式结果为真，则返回0，if把0值引向then |
| if test expression_r_r_r then | 表达式结果为假，则返回非0，if把非0值引向then |
[ ] && ——快捷if
| [ -f "/etc/shadow" ] && echo "This computer uses shadow passwors" |
| && 可以理解为then 如果左边的表达式为真则执行右边的语句 |
shell的if与c语言if的功能上的区别
| shell if | c语言if |
| 0为真，走then | 正好相反，非0走then |
| 不支持整数变量直接if 必须:if [ i –ne 0 ] 但支持字符串变量直接if if [ str ] 如果字符串非0 | 支持变量直接if if (i ) |
=================================以command作为if 条件===================================
以多条command或者函数作为if 条件
| echo –n “input:” read user if 多条指令,这些命令之间相当于“and”（与） grep $user /etc/passwd >/tmp/null who -u | grep $user then 上边的指令都执行成功,返回值$?为0，0为真，运行then echo "$user has logged" else 指令执行失败，$?为1，运行else echo "$user has not logged" fi |
| # sh test.sh input : macg macg pts/0 May 15 15:55 . 2075 (192.168.1.100) macg has logged # sh test.sh input : ddd ddd has not logged |
以函数作为if条件 (函数就相当于command,函数的优点是其return值可以自定义)
| if 以函数作为if条件， getyn then 函数reture值0为真，走then echo " your answer is yes" else 函数return值非0为假，走else echo "your anser is no" fi |
if command 等价于 command+if $?
| $ vi testsh.sh #!/bin/sh if cat 111-tmp.txt | grep ting1 then echo found else echo "no found" fi | $ vi testsh.sh #!/bin/sh cat 111-tmp.txt | grep ting1 if [ $? -eq 0 ] then echo $? echo found else echo $? echo "no found" fi |
| $ sh testsh.sh no found | $ sh testsh.sh 1 no found |
| $ vi 111-tmp.txt that is 222file thisting1 is 111file $ sh testsh.sh thisting1 is 111file found | $ vi 111-tmp.txt that is 222file thisting1 is 111file $ sh testsh.sh thisting1 is 111file found |
========================================以条件表达式作为 if条件=============================
传统if 从句子——以条件表达式作为 if条件
if [ 条件表达式 ]
then
command
command
command
else
command
command
fi
条件表达式
- 文件表达式
if [ -f file ] 如果文件存在
if [ -d ... ] 如果目录存在
if [ -s file ] 如果文件存在且非空
if [ -r file ] 如果文件存在且可读
if [ -w file ] 如果文件存在且可写
if [ -x file ] 如果文件存在且可执行
- 整数变量表达式
if [ int1 -eq int2 ] 如果int1等于int2
if [ int1 -ne int2 ] 如果不等于
if [ int1 -ge int2 ] 如果>=
if [ int1 -gt int2 ] 如果>
if [ int1 -le int2 ] 如果<=
if [ int1 -lt int2 ] 如果<
- 字符串变量表达式
If [ $a = $b ] 如果string1等于string2
字符串允许使用赋值号做等号
if [ $string1 != $string2 ] 如果string1不等于string2
if [ -n $string ] 如果string 非空(非0），返回0(true)
if [ -z $string ] 如果string 为空
if [ $sting ] 如果string 非空，返回0 (和-n类似)
条件表达式引用变量要带$
| if [ a = b ] ;then echo equal else echo no equal fi |
| [[email protected] ~]$ sh test.sh input a: 5 input b: 5 no equal （等于表达式没比较$a和$b,而是比较和a和b,自然a!=b) |
改正：
| if [ $a = $b ] ;then echo equal else echo no equal fi |
| [[email protected] ~]$ sh test.sh input a: 5 input b: 5 equal |
-eq -ne -lt -nt只能用于整数，不适用于字符串，字符串等于用赋值号=
| [[email protected] ~]$ vi test.sh echo -n "input your choice:" read var if [ $var -eq "yes" ] then echo $var fi [[email protected] ~]$ sh -x test.sh input your choice: y test.sh: line 3: test: y: integer expression_r_r_r expected 期望整数形式，即-eq不支持字符串 |
=放在别的地方是赋值,放在if [ ] 里就是字符串等于,shell里面没有==的,那是c语言的等于
无空格的字符串，可以加" ",也可以不加
| [[email protected] ~]$ vi test.sh echo "input a:" read a echo "input is $a" if [ $a = 123 ] ; then echo equal123 fi |
| [[email protected] ~]$ sh test.sh input a: 123 input is 123 equal123 |
= 作为等于时，其两边都必须加空格，否则失效
等号也是操作符，必须和其他变量，关键字，用空格格开 (等号做赋值号时正好相反，两边不能有空格）
| [[email protected] ~]$ vi test.sh echo "input your choice:" read var if [ $var="yes" ] then echo $var echo "input is correct" else echo $var echo "input error" fi | [[email protected] ~]$ vi test.sh echo "input your choice:" read var if [ $var = "yes" ] 在等号两边加空格 then echo $var echo "input is correct" else echo $var echo "input error" fi |
| [[email protected] ~]$ sh test.sh input your choice: y y input is correct [[email protected] ~]$ sh test.sh input your choice: n n input is correct 输错了也走then,都走then,为什么? 因为if把$var="yes"连读成一个变量，而此变量为空，返回1，则走else | [[email protected] ~]$ sh test.sh input your choice: y y input error [[email protected] ~]$ sh test.sh input your choice: no no input error 一切正常 |
If [ $ANS ] 等价于 if [ -n $ANS ]
如果字符串变量非空（then） , 空(else)
| echo "input your choice:" read ANS if [ $ANS ] then echo no empty else echo empth fi |
| [[email protected] ~]$ sh test.sh input your choice: 回车 empth 说明“回车”就是空串 [[email protected] ~]$ sh test.sh input your choice: 34 no empty |
整数条件表达式，大于，小于 ，s hell里没有> 和< ,会被当作尖括号，只有-ge,-gt,-le,lt
| [[email protected] ~]$ vi test.sh echo "input a:" read a if [ $a -ge 100 ] ; then echo 3bit else echo 2bit fi |
| [[email protected] ~]$ sh test.sh input a: 123 3bit [[email protected] ~]$ sh test.sh input a: 20 2bit |
整数操作符号-ge,-gt,-le,-lt, 别忘了加-
| if test $a ge 100 ; then [[email protected] ~]$ sh test.sh test.sh: line 4: test: ge: binary operator expected |
| if test $a -ge 100 ; then [[email protected] ~]$ sh test.sh input a: 123 3bit |
============================逻辑表达式=========================================
逻辑非 ! 条件表达式的相反
if [ ! 表达式 ]
if [ ! -d $num ] 如果不存在目录$num
逻辑与 –a 条件表达式的并列
if [ 表达式1 –a 表达式2 ]
逻辑或 -o 条件表达式的或
if [ 表达式1 –o 表达式2 ]
逻辑表达式
- 表达式与前面的= != -d –f –x -ne -eq -lt等合用
- 逻辑符号就正常的接其他表达式，没有任何括号（ ），就是并列
if [ -z "$JHHOME" -a -d $HOME/$num ]
- 注意逻辑与-a与逻辑或-o很容易和其他字符串或文件的运算符号搞混了
最常见的赋值形式，赋值前对=两边的变量都进行评测
左边测变量是否为空，右边测目录(值)是否存在（值是否有效）
| [[email protected] ~]$ vi test.sh : echo "input the num:" read num echo "input is $num" if [ -z "$JHHOME" -a -d $HOME/$num ] 如果变量$JHHOME为空，且$HOME/$num目录存在 then JHHOME=$HOME/$num 则赋值 fi echo "JHHOME is $JHHOME" |
| ----------------------- [[email protected] ~]$ sh test.sh input the num: ppp input is ppp JHHOME is 目录-d $HOME/$num 不存在，所以$JHHOME没被then赋值 |
| [[email protected] ~]$ mkdir ppp [[email protected] ~]$ sh test.sh input the num: ppp input is ppp JHHOME is /home/macg/ppp |
一个-o的例子，其中却揭示了”=”必须两边留空格的问题
| echo "input your choice:" read ANS if [ $ANS="Yes" -o $ANS="yes" -o $ANS="y" -o $ANS="Y" ] then ANS="y" else ANS="n" fi echo $ANS |
| [[email protected] ~]$ sh test.sh input your choice: n y [[email protected] ~]$ sh test.sh input your choice: no y 为什么输入不是yes,结果仍是y(走then） 因为=被连读了，成了变量$ANS="Yes"，而变量又为空，所以走else了 |
| [[email protected] ~]$ vi test.sh echo "input your choice:" read ANS echo "input your choice:" read ANS if [ $ANS = "Yes" -o $ANS = "yes" -o $ANS = "y" -o $ANS = "Y" ] then ANS="y" else ANS="n" fi echo $ANS |
| [[email protected] ~]$ sh test.sh input your choice: no n [[email protected] ~]$ sh test.sh input your choice: yes y [[email protected] ~]$ sh test.sh input your choice: y y |
===================以 test 条件表达式作为if条件===================================
if test $num -eq 0 等价于 if [ $num –eq 0 ]
test 表达式,没有 [ ]
if test $num -eq 0
then
echo "try again"
else
echo "good"
fi
man test
| [[email protected] ~]$ man test [(1) User Commands [(1) SYNOPSIS test EXPRESSION [ EXPRESSION ] [-n] STRING the length of STRING is nonzero -n和直接$str都是非0条件 -z STRING the length of STRING is zero STRING1 = STRING2 the strings are equal STRING1 != STRING2 the strings are not equal INTEGER1 -eq INTEGER2 INTEGER1 is equal to INTEGER2 INTEGER1 -ge INTEGER2 INTEGER1 is greater than or equal to INTEGER2 INTEGER1 -gt INTEGER2 INTEGER1 is greater than INTEGER2 INTEGER1 -le INTEGER2 INTEGER1 is less than or equal to INTEGER2 INTEGER1 -lt INTEGER2 INTEGER1 is less than INTEGER2 INTEGER1 -ne INTEGER2 INTEGER1 is not equal to INTEGER2 FILE1 -nt FILE2 FILE1 is newer (modification date) than FILE2 FILE1 -ot FILE2 FILE1 is older than FILE2 -b FILE FILE exists and is block special -c FILE FILE exists and is character special -d FILE FILE exists and is a directory -e FILE FILE exists 文件存在 -f FILE FILE exists and is a regular file 文件存在且是普通文件 -h FILE FILE exists and is a symbolic link (same as -L) -L FILE FILE exists and is a symbolic link (same as -h) -G FILE FILE exists and is owned by the effective group ID -O FILE FILE exists and is owned by the effective user ID -p FILE FILE exists and is a named pipe -s FILE FILE exists and has a size greater than zero -S FILE FILE exists and is a socket -w FILE FILE exists and is writable -x FILE FILE exists and is executable |
======================if简化语句=================================
最常用的简化if语句
| && 如果是“前面”，则“后面” [ -f /var/run/dhcpd.pid ] && rm /var/run/dhcpd.pid 检查 文件是否存在，如果存在就删掉 |
| || 如果不是“前面”，则后面 [ -f /usr/sbin/dhcpd ] || exit 0 检验文件是否存在，如果存在就退出 |
用简化 if 和$1,$2,$3来检测参数，不合理就调用help
[ -z "$1" ] && help 如果第一个参数不存在（-z 字符串长度为0 ）
[ "$1" = "-h" ] && help 如果第一个参数是-h,就显示help
例子
#!/bin/sh
[ -f "/etc/sysconfig/network-scripts/ifcfg-eth0" ] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth0
cp ifcfg-eth0.bridge /etc/sysconfig/network-scripts/ifcfg-eth0
[ -f "/etc/sysconfig/network-scripts/ifcfg-eth1" ] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth1
cp ifcfg-eth1.bridge /etc/sysconfig/network-scripts/ifcfg-eth1
[ -f "/etc/sysconfig/network-scripts/ifcfg-eth0:1" ] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth0:1
case语句格式
| # vi test.sh : echo "input : " read num echo "the input data is $num" case $num in 1) echo "January";; 双分号结束 2) echo "Feburary";; 5) echo "may" 每个case可以有多条命令 echo "sdfd" echo "sdf";; 但最后一条命令一定是双分号结束 *) echo "not correct input";; *）是其他值、default的意思 esac |
| # sh ./test.sh input : 2 the input data is 2 Feburary # sh ./test.sh input : ter the input data is ter not correct input |
case 语句如果某个选项没有任何语句，也要加;; 否则会出下边错误
test: line 166: syntax error near unexpected token `)'
test: line 166: `"system hostname config")'
为什么输入no,仍不匹配到[no]
原来[]是专门针对 单字符 的值,如果用[no],就是n和o之一
| case $yn in [no]) return 1;; * ) echo "only accept Y,y,N,n,YES,yes,NO,no" >&2;; |
| [[email protected] ~]$ sh test.sh enter y/n : no only accept Y,y,N,n,YES,yes,NO,no |
改正
| case $yn in no) return 1;; NO) return 1;; * ) echo "only accept Y,y,N,n,YES,yes,NO,no" >&2;; esac |
| [[email protected] ~]$ sh test.sh enter y/n : no |
一个getyn()函数的例子
| getyn( ) { while echo "enter y/n :" do read yn case $yn in [Yy]) return 0 ;; yes) return 0 ;; YES) return 0 ;; [Nn]) return 1 ;; no) return 1;; NO) return 1;; * ) echo "only accept Y,y,N,n,YES,yes,NO,no" ;; esac done } |
| if getyn 调用函数 以函数作为if条件,必须用if command法 then 注意0为真 echo " your answer is yes" else echo "your anser is no" fi |
if, case，匹配字符串最常见，但如何匹配一段很长的输出，一堆文字？最好方法，用“*”，如：*"command not found"*
| [[email protected] ~]$ vi test.sh var=$(ls -l $1) $()取命令输出，$1是命令行参数 echo "output is $var" case $var in "-rw-rw-r--"*) echo "this is not a execute file";; "-rwxrwxr-x"*) echo "this is a execute file"; 注意*在双引号外边 esac |
| [[email protected] ~]$ sh test.sh 22.txt output is -rw-rw-r-- 1 macg macg 15 Jun 9 19:00 22.txt this is not a execute file [[email protected] ~]$ chmod +x 22.txt [[email protected] ~]$ sh test.sh 22.txt output is -rwxrwxr-x 1 macg macg 15 Jun 9 19:00 22.txt this is a execute file |
例2．匹配file命令输出的一堆文字,以获知文件类型
用’ ’ 取输出,然后用CASE+*对输出做修饰处理.
| [[email protected] ~]$ vi test.sh var=`file $1` ` `和$( )作用相同，是取命令输出 echo "output is $var" case $var in "$1: ASCII text"*) echo "this is a text file";; "$1: directory"*) echo "this is a directory";; 注意*在双引号外边 esac |
| [[email protected] ~]$ sh test.sh 22.txt output is 22.txt: ASCII text this is a text file [[email protected] ~]$ sh test.sh test-dir output is test-dir: directory this is a directory |
最典型的shell case命令匹配命令行，用于sys v启动脚本的start|stop|restart|status处理
case "$@" in
($@ 字符串数组：以"参数1" "参数2" ... 的字符串数组形式保存所有参数
对于单个参数的情况，$@就是一个字符串)
start)
echo -n "Starting firewall..."
。。。
echo "OK!"
exit 0
;;
stop)
echo -n "Stopping firewall..."
。。。
exit 0
;;
restart )
$0 stop $0即执行原始程序
$0 start
;;
status)
clear
echo ">------------------------------------------"
iptables -L
echo ">------------------------------------------"
iptables -t nat -L POSTROUTING
exit 0
*)
echo "Usage: $0 {start|stop|restart|status}"
exit 1
esac
=====================================while语句========================================
while语句格式
| while 表达式 do command command done |
while 和 if 的条件表达式完全相同，也是[ ] 或commad或test
| While 表达式 | If 表达式 |
| 表达式值为0，则循环继续 | 表达式值为0，then |
| 表达式值为非0，则循环停止 | 表达式值为非0,else |
最基本的i++ 条件型循环
| i=1 while [ $i -lt 10 ] do sed -n "${i}p" 111.txt i=$(($i+1)) 必须双层括号 done |
命令型while 循环
while command 命令返回值0（成功执行），循环继续
| pause函数，输入任何值继续，输入q退出程序 pause() { while echo "Press <return> to proceed or type q to quit:" do read cmd case $cmd in [qQ]) exit 1;; exit直接退到底，退出shell script "") break;; break跳出循环 *) continue;; continue跳到循环底，重新开始新循环循环 esac done |
While echo … 此命令没有失败的可能，所以必须有break,return,exit之类的指令
while 关键字
break———— 用来跳出循环
continue—— 用来不执行余下的部分，直接跳到下一个循环
===========================================FOR语句===================================
for语句格式
| for 表达式 do command command done |
i++,n=n+1 必须用双层括号 $(($num+1)) ，单层括号$($num+1)不管用
| [[email protected] home]# vi test.sh : echo "input num:" read num echo "input is $num" num=$($num+1) echo "new num is $num" [[email protected] home]# sh test.sh input num: 3 input is 3 test.sh: line 6: 3+1: command not found new num is |
| [[email protected] home]# vi test.sh : echo "input num:" read num echo "input is $num" num=$(($num+1)) echo "new num is $num" [[email protected] home]# sh test.sh input num: 3 input is 3 new num is 4 |
(( ))与[ ]作用完全相同
| echo input: read i i=$(($i+1)) echo $i | echo input: read i i=$[$i+1] echo $i |
| [[email protected] ~]$ sh ttt.sh input: 6 7 | [[email protected] ~]$ sh ttt.sh input: 6 7 |
再证明(( ))与[ ]完全相同--------if (( ))
| if (( $# != 3 )); then echo "usage: $0 host user passwd" exit 1 fi | if [ $# != 3 ]; then echo "usage: $0 host user passwd" exit 1 fi |
| [[email protected] ~]$ sh ttt.sh 1 2 usage: ttt.sh host user passwd | [[email protected] ~]$ sh ttt.sh 1 2 usage: ttt.sh host user passwd |
$foo=$(($foo+1)) # 运行的时候这个地方报错
给变量赋值,左边的变量不需要加 $ 符号,
foo=$(($foo+1))
赋值=,read,export都不需要加变量$