Linux shell編程學習實例與參數分析（二）

第三章 shell的輸入和輸出
1.echo    echo [option] string
            -e 解析轉移字符
           -n 回車不換行，linux系統默認回車換行
            轉移字符 \c \t \f \n
#!/bin/bash
#echo
echo -e "this echo's 3 newlne\n\n\n"
echo "OK"
echo
echo "this is echo's 3 ewline\n\n\n"
echo "this log file have all been done">mylogfile.txt
[test@szbirdora ~]$ sh echod.sh
this echo's 3 newlne

 

OK

this is echo's 3 ewline\n\n\n
上面能夠看到有-e則能夠解析轉移字符，沒有不能解析。echo空輸出爲空

2.read 能夠從鍵盤或文件的某一行文本中讀入信息，並將其賦給一個變量
read variable1 variable2
eg.
#!/bin/bash
#readname
echo -n "first name:"
read firstname
echo -n "last name:"
read lastname
echo "this name is $firstname $lastname"

3.cat        顯示文件的內容，建立內容，還能夠顯示控制字符
            cat [options]filename1 filename2
                   -v   顯示控制字符（Windows文件）
             cat命令不會分頁顯示，要分頁能夠採用more、less

4.管道|

5.tee     把輸出的一個副本輸送到標準輸出，另外一個副本拷貝到相應的文件中,通常與管道合用
              tee [options] files
              -a 在文件中追加
eg.
[test@szbirdora 1]$ echo |tee myfile

[test@szbirdora 1]$ cat myfile

將myfile文件置空

6.文件重定向
command>filename                                        ---覆蓋輸出
command>>filename                                      ---追加輸出
command>filename>&1                                 ---把標準輸出和標準錯誤重定向
command<<delimiter                                     ---輸入直到delimiter分解符
command<filename                                       ----輸入文件內容到命令
command<-                                                     --- 關閉標準輸入
>nullfile.txt                                                       ---建立字節爲0的文件
command1<filename>command3               ---按從左到右順序執行
eg.
說明：myfile爲空間
[test@szbirdora 1]$ df -lh>myfile
[test@szbirdora 1]$ cat myfile
Filesystem            Size Used Avail Use% Mounted on
/dev/sda1              20G 3.3G   16G 18% /
none                  2.0G     0 2.0G   0% /dev/shm
/dev/sda2              79G   17G   59G 23% /u01
/dev/sda4              28G 3.9G   22G 15% /u02
[test@szbirdora 1]$ df -lh>myfile
[test@szbirdora 1]$ cat myfile
Filesystem            Size Used Avail Use% Mounted on
/dev/sda1              20G 3.3G   16G 18% /
none                  2.0G     0 2.0G   0% /dev/shm
/dev/sda2              79G   17G   59G 23% /u01
/dev/sda4              28G 3.9G   22G 15% /u02
[test@szbirdora 1]$ df -lh>>myfile
[test@szbirdora 1]$ cat myfile
Filesystem            Size Used Avail Use% Mounted on
/dev/sda1              20G 3.3G   16G 18% /
none                  2.0G     0 2.0G   0% /dev/shm
/dev/sda2              79G   17G   59G 23% /u01
/dev/sda4              28G 3.9G   22G 15% /u02
Filesystem            Size Used Avail Use% Mounted on
/dev/sda1              20G 3.3G   16G 18% /
none                  2.0G     0 2.0G   0% /dev/shm
/dev/sda2              79G   17G   59G 23% /u01
/dev/sda4              28G 3.9G   22G 15% /u02
[test@szbirdora 1]$ cat >>myfile<<exit
> China
> Hubei
> Suizhou
> exit
[test@szbirdora 1]$ cat myfile
China
Hubei
Suizhou

7.exec        能夠用來替代當前shell。現有任何環境變量都會清除

第四章 控制流結構
1.if語句
if 條件1
then
     命令1
elif 條件2
then
     命令2
else
     命令3
fi
------------------
if 條件
then 命令
fi
eg：
#!/bin/bash
#if test
#this is a comment line
if [ "10" -lt "12" ];then
#yes 10 is less than 12
echo "yes,10 is less than 12"
else
echo "no"
fi
注意：if語句必須以fi終止
   "10" 前一個空格，「12」後也有一個空格。這個條件都是經過test命令來指定。條件表達爲test expression或者[expression]

條件表達式中的比較函數
man test
NAME
       test - check file types and compare values

SYNOPSIS
       test EXPRESSION
       [ EXPRESSION ]
       [ OPTION

DESCRIPTION
       Exit with the status determined by EXPRESSION.

       --help display this help and exit

       --version
              output version information and exit

       EXPRESSION is true or false and sets exit status. It is one of:

       ( EXPRESSION )
              EXPRESSION is true

       ! EXPRESSION
              EXPRESSION is false

       EXPRESSION1 -a EXPRESSION2
              both EXPRESSION1 and EXPRESSION2 are true

       EXPRESSION1 -o EXPRESSION2
              either EXPRESSION1 or EXPRESSION2 is true

       [-n] STRING
              the length of STRING is nonzero

       -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 -ef FILE2
              FILE1 and FILE2 have the same device and inode numbers

       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

       -f FILE
              FILE exists and is a regular file
       -g FILE
              FILE exists and is set-group-ID

       -h FILE
              FILE exists and is a symbolic link (same as -L)

       -G FILE
              FILE exists and is owned by the effective group ID

       -k FILE
              FILE exists and has its sticky bit set

       -L FILE
              FILE exists and is a symbolic link (same as -h)

       -O FILE
              FILE exists and is owned by the effective user ID

       -p FILE
              FILE exists and is a named pipe

       -r FILE
              FILE exists and is readable

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t [FD]
              file descriptor FD (stdout by default) is opened on a terminal

       -u FILE
              FILE exists and its set-user-ID bit is set

       -w FILE
              FILE exists and is writable

       -x FILE
             FILE exists and is executable

eg.
#!/bin/bash
#if test
#this is a comment line
echo "Enter your filename:"
read myfile
if [ -e $myfile ]
then
   if [ -s $myfile ];then
    echo "$myfile exist and size greater than zero"
   else
    echo "$myfile exist but size is zero"
   fi
else
echo "file no exist"
fi
[test@szbirdora 1]$ sh iftest.sh
Enter your filename:
11
11 exist but size is zero

2.case語句
case語句爲多選擇語句。
case 值 in
模式1）
    命令1
    ;;
模式2)
    命令2
    ;;
esac
eg.
#!/bin/bash
#case select
echo -n "enter a number from 1 to 3:"
read ans
case $ans in
1)
echo "you select 1"
;;
2)
echo "you select 2"
;;
3)
echo "you select 3"
;;
*)
echo "`basename $0`:this is not between 1 and 3">&2
exit;
;;
esac

3.for 循環
for循環通常格式：
for 變量名 in 列表 (列表以空格做爲分割)
do
   命令1
   命令2
done

eg：
#!/bin/bash
#forlist1
for loop in 1 2 3 4 5
do
echo $loop
done

4.until循環
until 條件
do
   命令1
   命令2
   ...
done
條件測試發生在循環末尾，因此循環至少能夠執行一次。

5.
while循環
while 命令 （能夠是一個命令也能夠是多個，作條件測試）
do
      命令1
      命令2
      ...
done
注意：若是從文件中讀入變量<filename要放到done後

6.break和continue控制
break跳出，continue跳過