Linux shell编程学习实例与参数分析（二）
第三章 shell的输入和输出1.echo echo string
-e 解析转移字符
-n 回车不换行，linux系统默认回车换行
转移字符 \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
$ sh echod.sh
this echo's 3 newlne
OK
this is echo's 3 ewline\n\n\n
上面可以看到有-e则可以解析转移字符，没有不能解析。echo空输出为空
2.read 可以从键盘或文件的某一行文本中读入信息，并将其赋给一个变量
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 显示文件的内容，创建内容，还可以显示控制字符
cat filename1 filename2
-v 显示控制字符（Windows文件）
cat命令不会分页显示，要分页可以采用more、less
4.管道|
5.tee 把输出的一个副本输送到标准输出，另一个副本拷贝到相应的文件中,一般与管道合用
tee files
-a 在文件中追加
eg.
$ echo |tee myfile
$ cat myfile
将myfile文件置空
6.文件重定向
command>filename ---覆盖输出
command>>filename ---追加输出
command>filename>&1 ---把标准输出和标准错误重定向
commandmyfile
$ cat myfile
Filesystem > /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
$ df -lh>>myfile
$ cat myfile
Filesystem > /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 > /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
$ cat >>myfile Hubei
> Suizhou
> exit
$ cat myfile
China
Hubei
Suizhou
7.exec 可以用来替代当前shell。现有任何环境变量都会清除
第四章 控制流结构
1.if语句
if 条件1
then
命令1
elif 条件2
then
命令2
else
命令3
fi
------------------
if 条件
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语句必须以fi终止
"10" 前一个空格，“12”后也有一个空格。这个条件都是通过test命令来指定。条件表达为test expression或者
条件表达式中的比较函数
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> -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> -p FILE
FILE exists and is a named pipe
-r FILE
FILE exists and is readable
-s FILE
FILE exists and has a> -S FILE
FILE exists and is a socket
-t
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> else
echo "$myfile exist but> fi
else
echo "file no exist"
fi
$ sh iftest.sh
Enter your filename:
11
11 exist but> 2.case语句
case语句为多选择语句。
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 循环
for循环一般格式：
for 变量名 in 列表 (列表以空格作为分割)
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循环
until 条件
do
命令1
命令2
...
done
条件测试发生在循环末尾，所以循环至少可以执行一次。
5.
while循环
while 命令 （可以是一个命令也可以是多个，做条件测试）
do
命令1
命令2
...
done
注意：如果从文件中读入变量
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