http://blog.csdn.net/hainan16/article/category/861739
if 語句格式
| if 條件 then Command else Command fi 别忘了這個結尾 |
| If語句忘了結尾fi test.sh: line 14: syntax error: unexpected end of fi |
if 的三種條件表達式
| if command then if 函數 then | 指令執行成功，等于傳回0 （比如grep ,找到比對） 執行失敗，傳回非0 （grep,沒找到比對） |
| if [ expression_r_r_r ] then | 表達式結果為真，則傳回0，if把0值引向then |
| if test expression_r_r_r then | 表達式結果為假，則傳回非0，if把非0值引向then |
[ ] && ——快捷if
| [ -f "/etc/shadow" ] && echo "This computer uses shadow passwors" |
| && 可以了解為then 如果左邊的表達式為真則執行右邊的語句 |
shell的if與c語言if的功能上的差別
| shell if | c語言if |
| 0為真，走then | 正好相反，非0走then |
| 不支援整數變量直接if 必須:if [ i –ne 0 ] 但支援字元串變量直接if if [ str ] 如果字元串非0 | 支援變量直接if if (i ) |
=================================以command作為if 條件===================================
以多條command或者函數作為if 條件
| echo –n “input:” read user if 多條指令,這些指令之間相當于“and”（與） grep $user /etc/passwd >/tmp/null who -u | grep $user then 上邊的指令都執行成功,傳回值$?為0，0為真，運作then echo "$user has logged" else 指令執行失敗，$?為1，運作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 |
以函數作為if條件 (函數就相當于command,函數的優點是其return值可以自定義)
| if 以函數作為if條件， getyn then 函數reture值0為真，走then echo " your answer is yes" else 函數return值非0為假，走else echo "your anser is no" fi |
if command 等價于 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 |
========================================以條件表達式作為 if條件=============================
傳統if 從句子——以條件表達式作為 if條件
if [ 條件表達式 ]
then
command
command
command
else
command
command
fi
條件表達式
- 檔案表達式
if [ -f file ] 如果檔案存在
if [ -d ... ] 如果目錄存在
if [ -s file ] 如果檔案存在且非空
if [ -r file ] 如果檔案存在且可讀
if [ -w file ] 如果檔案存在且可寫
if [ -x file ] 如果檔案存在且可執行
- 整數變量表達式
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<
- 字元串變量表達式
If [ $a = $b ] 如果string1等于string2
字元串允許使用指派号做等号
if [ $string1 != $string2 ] 如果string1不等于string2
if [ -n $string ] 如果string 非空(非0），傳回0(true)
if [ -z $string ] 如果string 為空
if [ $sting ] 如果string 非空，傳回0 (和-n類似)
條件表達式引用變量要帶$
| if [ a = b ] ;then echo equal else echo no equal fi |
| [[email protected] ~]$ sh test.sh input a: 5 input b: 5 no equal （等于表達式沒比較$a和$b,而是比較和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隻能用于整數，不适用于字元串，字元串等于用指派号=
| [[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 期望整數形式，即-eq不支援字元串 |
=放在别的地方是指派,放在if [ ] 裡就是字元串等于,shell裡面沒有==的,那是c語言的等于
無空格的字元串，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 |
= 作為等于時，其兩邊都必須加空格，否則失效
等号也是操作符，必須和其他變量，關鍵字，用空格格開 (等号做指派号時正好相反，兩邊不能有空格）
| [[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" ] 在等号兩邊加空格 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 輸錯了也走then,都走then,為什麼? 因為if把$var="yes"連讀成一個變量，而此變量為空，傳回1，則走else | [[email protected] ~]$ 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 ] 等價于 if [ -n $ANS ]
如果字元串變量非空（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: 回車 empth 說明“回車”就是空串 [[email protected] ~]$ sh test.sh input your choice: 34 no empty |
整數條件表達式，大于，小于 ，s hell裡沒有> 和< ,會被當作尖括号，隻有-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 |
整數操作符号-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 |
============================邏輯表達式=========================================
邏輯非 ! 條件表達式的相反
if [ ! 表達式 ]
if [ ! -d $num ] 如果不存在目錄$num
邏輯與 –a 條件表達式的并列
if [ 表達式1 –a 表達式2 ]
邏輯或 -o 條件表達式的或
if [ 表達式1 –o 表達式2 ]
邏輯表達式
- 表達式與前面的= != -d –f –x -ne -eq -lt等合用
- 邏輯符号就正常的接其他表達式，沒有任何括号（ ），就是并列
if [ -z "$JHHOME" -a -d $HOME/$num ]
- 注意邏輯與-a與邏輯或-o很容易和其他字元串或檔案的運算符号搞混了
最常見的指派形式，指派前對=兩邊的變量都進行評測
左邊測變量是否為空，右邊測目錄(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 ] 如果變量$JHHOME為空，且$HOME/$num目錄存在 then JHHOME=$HOME/$num 則指派 fi echo "JHHOME is $JHHOME" |
| ----------------------- [[email protected] ~]$ sh test.sh input the num: ppp input is ppp JHHOME is 目錄-d $HOME/$num 不存在，是以$JHHOME沒被then指派 |
| [[email protected] ~]$ mkdir ppp [[email protected] ~]$ sh test.sh input the num: ppp input is ppp JHHOME is /home/macg/ppp |
一個-o的例子，其中卻揭示了”=”必須兩邊留白格的問題
| 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 為什麼輸入不是yes,結果仍是y(走then） 因為=被連讀了，成了變量$ANS="Yes"，而變量又為空，是以走else了 |
| [[email protected] ~]$ 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 條件表達式作為if條件===================================
if test $num -eq 0 等價于 if [ $num –eq 0 ]
test 表達式,沒有 [ ]
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條件 -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 檔案存在 -f FILE FILE exists and is a regular file 檔案存在且是普通檔案 -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簡化語句=================================
最常用的簡化if語句
| && 如果是“前面”，則“後面” [ -f /var/run/dhcpd.pid ] && rm /var/run/dhcpd.pid 檢查 檔案是否存在，如果存在就删掉 |
| || 如果不是“前面”，則後面 [ -f /usr/sbin/dhcpd ] || exit 0 檢驗檔案是否存在，如果存在就退出 |
用簡化 if 和$1,$2,$3來檢測參數，不合理就調用help
[ -z "$1" ] && help 如果第一個參數不存在（-z 字元串長度為0 ）
[ "$1" = "-h" ] && help 如果第一個參數是-h,就顯示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語句格式
| # vi test.sh : echo "input : " read num echo "the input data is $num" case $num in 1) echo "January";; 雙分号結束 2) echo "Feburary";; 5) echo "may" 每個case可以有多條指令 echo "sdfd" echo "sdf";; 但最後一條指令一定是雙分号結束 *) 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 語句如果某個選項沒有任何語句，也要加;; 否則會出下邊錯誤
test: line 166: syntax error near unexpected token `)'
test: line 166: `"system hostname config")'
為什麼輸入no,仍不比對到[no]
原來[]是專門針對 單字元 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 |
一個getyn()函數的例子
| getyn( ) { while echo "enter y/n :" do read yn case $yn in [Yy]) return 0 ;; yes) return 0 ;; YES) return 0 ;; [Nn]) return 1 ;; no) return 1;; NO) return 1;; * ) echo "only accept Y,y,N,n,YES,yes,NO,no" ;; esac done } |
| if getyn 調用函數 以函數作為if條件,必須用if command法 then 注意0為真 echo " your answer is yes" else echo "your anser is no" fi |
if, case，比對字元串最常見，但如何比對一段很長的輸出，一堆文字？最好方法，用“*”，如：*"command not found"*
| [[email protected] ~]$ vi test.sh var=$(ls -l $1) $()取指令輸出，$1是指令行參數 echo "output is $var" case $var in "-rw-rw-r--"*) echo "this is not a execute file";; "-rwxrwxr-x"*) echo "this is a execute file"; 注意*在雙引号外邊 esac |
| [[email protected] ~]$ 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．比對file指令輸出的一堆文字,以獲知檔案類型
用’ ’ 取輸出,然後用CASE+*對輸出做修飾處理.
| [[email protected] ~]$ vi test.sh var=`file $1` ` `和$( )作用相同，是取指令輸出 echo "output is $var" case $var in "$1: ASCII text"*) echo "this is a text file";; "$1: directory"*) echo "this is a directory";; 注意*在雙引号外邊 esac |
| [[email protected] ~]$ 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指令比對指令行，用于sys v啟動腳本的start|stop|restart|status處理
case "$@" in
($@ 字元串數組：以"參數1" "參數2" ... 的字元串數組形式儲存所有參數
對于單個參數的情況，$@就是一個字元串)
start)
echo -n "Starting firewall..."
。。。
echo "OK!"
exit 0
;;
stop)
echo -n "Stopping firewall..."
。。。
exit 0
;;
restart )
$0 stop $0即執行原始程式
$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語句========================================
while語句格式
| while 表達式 do command command done |
while 和 if 的條件表達式完全相同，也是[ ] 或commad或test
| While 表達式 | If 表達式 |
| 表達式值為0，則循環繼續 | 表達式值為0，then |
| 表達式值為非0，則循環停止 | 表達式值為非0,else |
最基本的i++ 條件型循環
| i=1 while [ $i -lt 10 ] do sed -n "${i}p" 111.txt i=$(($i+1)) 必須雙層括号 done |
指令型while 循環
while command 指令傳回值0（成功執行），循環繼續
| pause函數，輸入任何值繼續，輸入q退出程式 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跳出循環 *) continue;; continue跳到循環底，重新開始新循環循環 esac done |
While echo … 此指令沒有失敗的可能，是以必須有break,return,exit之類的指令
while 關鍵字
break———— 用來跳出循環
continue—— 用來不執行餘下的部分，直接跳到下一個循環
===========================================FOR語句===================================
for語句格式
| for 表達式 do command command done |
i++,n=n+1 必須用雙層括号 $(($num+1)) ，單層括号$($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 $num" [[email protected] home]# sh test.sh input num: 3 input is 3 new num is 4 |
(( ))與[ ]作用完全相同
| echo input: read i i=$(($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 |
再證明(( ))與[ ]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)) # 運作的時候這個地方報錯
給變量指派,左邊的變量不需要加 $ 符号,
foo=$(($foo+1))
指派=,read,export都不需要加變量$