shell编程

$ echo '#!/bin/sh' > my-script.sh
$ echo 'echo Hello World' >> my-script.sh
$ chmod 755 my-script.sh
$ ./my-script.sh
Hello World
$

上面这段代码中，echo是打印的意思，而>是重定向的意思，chmod是修改权限的意思。shell脚本以.sh为结尾。

#!/bin/sh
# This is a comment!
echo Hello World    # This is a comment, too!

以上为my-script.sh中的代码，可以学习一下如何写注释。

$ chmod a+rx my-script.sh
$ ./my-script.sh

想要将shell脚本变成可执行的，可以使用以上语句。

grep "mystring" /tmp/myfile

这句的意思是将在/tmp/myfile中的"mystring"字符串搜索出来。

#!/bin/sh
# This is a comment!
echo Hello World        # This is a comment, too!

以上是first.sh中的代码。可以使用以下代码执行：

$ chmod 755 first.sh
$ ./first.sh
Hello World
$

得到结果：

$ echo Hello World
Hello World
$
#!/bin/sh
MY_MESSAGE="Hello World"
echo $MY_MESSAGE

以上是var.sh的代码。用来学习变量的使用。环境变量使用以下代码实现：

$ export name=zuoyuan
#!/bin/sh
echo What is your name?
read MY_NAME
echo "Hello $MY_NAME - hope you're well."

以上是var2.sh的代码。

#!/bin/sh
echo "What is your name?"
read USER_NAME
echo "Hello $USER_NAME"
echo "I will create you a file called ${USER_NAME}_file"
touch "${USER_NAME}_file"

以上代码可以创建一个文件，touch关键字的作用是如果有这个文件，不做任何操作，如果没有这个文件，就创建一个这个文件。

#!/bin/sh
for i in 1 2 3 4 5
do
  echo "Looping ... number $i"
done

以上是for循环。写入for.sh。

#!/bin/sh
for i in hello 1 * 2 goodbye
do
  echo "Looping ... i is set to $i"
done

继续for循环。写入for2.sh中。

#!/bin/sh
INPUT_STRING=hello
while [ "$INPUT_STRING" != "bye" ]
do
  echo "Please type something in (bye to quit)"
  read INPUT_STRING
  echo "You typed: $INPUT_STRING"
done

while循环。

#!/bin/sh
while :
do
  echo "Please type something in (^C to quit)"
  read INPUT_STRING
  echo "You typed: $INPUT_STRING"
done

继续while循环。

#!/bin/sh
while read f
do
  case $f in
    hello)        echo English    ;;
    howdy)        echo American    ;;
    gday)        echo Australian    ;;
    bonjour)    echo French    ;;
    "guten tag")    echo German    ;;
    *)        echo Unknown Language: $f
        ;;
   esac
done < myfile

使用while循环读取文件。

for runlevel in 0 1 2 3 4 5 6 S
do
  mkdir rc${runlevel}.d
done

批量建文件。

if [ ... ]
then
  # if-code
else
  # else-code
fi
if [ ... ]; then
  # do something
fi
if  [ something ]; then
 echo "Something"
 elif [ something_else ]; then
   echo "Something else"
 else
   echo "None of the above"
fi

以上是几种条件结构。

#!/bin/sh
if [ "$X" -lt "0" ]
then
  echo "X is less than zero"
fi
if [ "$X" -gt "0" ]; then
  echo "X is more than zero"
fi
[ "$X" -le "0" ] && 
      echo "X is less than or equal to  zero"
[ "$X" -ge "0" ] && 
      echo "X is more than or equal to zero"
[ "$X" = "0" ] && 
      echo "X is the string or number "0""
[ "$X" = "hello" ] && 
      echo "X matches the string "hello""
[ "$X" != "hello" ] && 
      echo "X is not the string "hello""
[ -n "$X" ] && 
      echo "X is of nonzero length"
[ -f "$X" ] && 
      echo "X is the path of a real file" || 
      echo "No such file: $X"
[ -x "$X" ] && 
      echo "X is the path of an executable file"
[ "$X" -nt "/etc/passwd" ] && 
      echo "X is a file which is newer than /etc/passwd"
echo -en "Please guess the magic number: "
read X
echo $X | grep "[^0-9]" > /dev/null 2>&1
if [ "$?" -eq "0" ]; then
  # If the grep found something other than 0-9
  # then it's not an integer.
  echo "Sorry, wanted a number"
else
  # The grep found only 0-9, so it's an integer. 
  # We can safely do a test on it.
  if [ "$X" -eq "7" ]; then
    echo "You entered the magic number!"
  fi
fi
#!/bin/sh
X=0
while [ -n "$X" ]
do
  echo "Enter some text (RETURN to quit)"
  read X
  echo "You said: $X"
done
#!/bin/sh
X=0
while [ -n "$X" ]
do
  echo "Enter some text (RETURN to quit)"
  read X
  if [ -n "$X" ]; then
    echo "You said: $X"
  fi
done
if [ "$X" -lt "0" ]
then
  echo "X is less than zero"
fi

..........  and  ........

if [ ! -n "$X" ]; then
  echo "You said: $X"
fi

以上是几个条件结构的例子。

继续举几个例子。

#!/bin/sh

echo "Please talk to me ..."
while :
do
  read INPUT_STRING
  case $INPUT_STRING in
    hello)
        echo "Hello yourself!"
        ;;
    bye)
        echo "See you again!"
        break
        ;;
    *)
        echo "Sorry, I don't understand"
        ;;
  esac
done
echo 
echo "That's all folks!"

运行后有以下结果。

$ ./talk.sh
Please talk to me ...
hello
Hello yourself!
What do you think of politics?
Sorry, I don't understand
bye
See you again!

That's all folks!
$

继续学习变量。以下代码写入var3.sh。

#!/bin/sh
echo "I was called with $# parameters"
echo "My name is $0"
echo "My first parameter is $1"
echo "My second parameter is $2"
echo "All parameters are $@"

运行结果如下：

$ /home/steve/var3.sh
I was called with 0 parameters
My name is /home/steve/var3.sh
My first parameter is
My second parameter is    
All parameters are 
$
$ ./var3.sh hello world earth
I was called with 3 parameters
My name is ./var3.sh
My first parameter is hello
My second parameter is world
All parameters are hello world earth

继续学习变量。以下代码写入var4.sh。

#!/bin/sh
while [ "$#" -gt "0" ]
do
  echo "$1 is $1"
  shift
done

This script keeps on using shift until $# is down to zero, at which point the list is empty. Another special variable is $?. This contains the exit value of the last run command. So the code:

#!/bin/sh
/usr/local/bin/my-command
if [ "$?" -ne "0" ]; then
  echo "Sorry, we had a problem there!"
fi

当进程退出时的代码为0时，就没有问题。

#!/bin/sh
old_IFS="$IFS"
IFS=:
echo "Please input some data separated by colons ..."
read x y z
IFS=$old_IFS
echo "x is $x y is $y z is $z"

写入var5.sh。运行如下：

$ ./ifs.sh
Please input some data separated by colons ...
hello:how are you:today
x is hello y is how are you z is today
$ ./ifs.sh
Please input some data separated by colons ...
hello:how are you:today:my:friend
x is hello y is how are you z is today:my:friend

使用默认变量。

#!/bin/sh
echo -en "What is your name [ `whoami` ] "
read myname
if [ -z "$myname" ]; then
  myname=`whoami`
fi
echo "Your name is : $myname"

函数的用法。

#!/bin/sh
# A simple script with a function...

add_a_user()
{
  USER=$1
  PASSWORD=$2
  shift; shift;
  # Having shifted twice, the rest is now comments ...
  COMMENTS=$@
  echo "Adding user $USER ..."
  echo useradd -c "$COMMENTS" $USER
  echo passwd $USER $PASSWORD
  echo "Added user $USER ($COMMENTS) with pass $PASSWORD"
}

###
# Main body of script starts here
###
echo "Start of script..."
add_a_user bob letmein Bob Holness the presenter
add_a_user fred badpassword Fred Durst the singer
add_a_user bilko worsepassword Sgt. Bilko the role model
echo "End of script..."

阶乘的shell实现，使用递归。

#!/bin/sh

factorial()
{
  if [ "$1" -gt "1" ]; then
    i=`expr $1 - 1`
    j=`factorial $i`
    k=`expr $1 * $j`
    echo $k
  else
    echo 1
  fi
}


while :
do
  echo "Enter a number:"
  read x
  factorial $x
done 

模块化编程。以下代码写入common.lib。

# common.lib
# Note no #!/bin/sh as this should not spawn 
# an extra shell. It's not the end of the world 
# to have one, but clearer not to.
#
STD_MSG="About to rename some files..."

rename()
{
  # expects to be called as: rename .txt .bak 
  FROM=$1
  TO=$2

  for i in *$FROM
  do
    j=`basename $i $FROM`
    mv $i ${j}$TO
  done
}

以下代码写入function2.sh。

#!/bin/sh
# function2.sh
. ./common.lib
echo $STD_MSG
rename .txt .bak

返回码。

#!/bin/sh

adduser()
{
  USER=$1
  PASSWORD=$2
  shift ; shift
  COMMENTS=$@
  useradd -c "${COMMENTS}" $USER
  if [ "$?" -ne "0" ]; then
    echo "Useradd failed"
    return 1
  fi
  passwd $USER $PASSWORD
  if [ "$?" -ne "0" ]; then
    echo "Setting password failed"
    return 2
  fi
  echo "Added user $USER ($COMMENTS) with pass $PASSWORD"
}

## Main script starts here

adduser bob letmein Bob Holness from Blockbusters
ADDUSER_RETURN_CODE=$?
if [ "$ADDUSER_RETURN_CODE" -eq "1" ]; then
  echo "Something went wrong with useradd"
elif [ "$ADDUSER_RETURN_CODE" -eq "2" ]; then 
   echo "Something went wrong with passwd"
else
  echo "Bob Holness added to the system."
fi

crontab的使用

在考虑向cron进程提交一个crontab文件之前，首先要做的一件事情就是设置环境变量EDITOR。cron进程根据它来确定使用哪个编辑器编辑crontab文件。9 9 %的UNIX和LINUX用户都使用vi，如果你也是这样，那么你就编辑$ HOME目录下的. profile文件，在其中加入这样一行：

EDITOR=vi; export EDITOR

然后保存并退出。不妨创建一个名为<user>cron的文件，其中<user>是用户名，例如，davecron。在该文件中加入如下的内容。

# (put your own initials here)echo the date to the console every
# 15minutes between 6pm and 6am
0,15,30,45 18-06 * * * /bin/echo 'date' > /dev/console

保存并退出。确信前面5个域用空格分隔。

在上面的例子中，系统将每隔1 5分钟向控制台输出一次当前时间。如果系统崩溃或挂起，从最后所显示的时间就可以一眼看出系统是什么时间停止工作的。在有些系统中，用tty1来表示控制台，可以根据实际情况对上面的例子进行相应的修改。为了提交你刚刚创建的crontab文件，可以把这个新创建的文件作为cron命令的参数：

$ crontab davecron

现在该文件已经提交给cron进程，它将每隔15分钟运行一次。

同时，新创建文件的一个副本已经被放在/var/spool/cron目录中，文件名就是用户名(即dave)。

为了列出crontab文件，可以用：

$ crontab -l