Shell流程控制（if,else,case,while,for,until）

1.条件选择

---

1.1.if 语句

　　语法

#!/bin/bash

MATH_SCORES="$1"
NAME="$2"

if [ -z "${MATH_SCORES}" ]
then
  printf "The command requires that options have a scores.\n"
  printf "What's ths scores of your math? :"
  read MATH_SCORES
fi

if [ -z "${NAME}" ]
then
  printf "The command requires that options have a student's name.\n"
  printf "What's your name? :"
  read NAME
fi

if [ "${NAME}" = "sunny" ]
then
  printf "No, sunny is a teacher.\nPleae input your name,ok? "
  read NAME
  printf "My god,i think, you are bann sunny, excuse me.\n\n"
else
  printf "\n"
fi

if [ "${MATH_SCORES}" -ge  ]
then
  echo "Your scores is very good.Congratulations to you, ${NAME}."
  echo "I hope that you are't sunny."
else if [ "${MATH_SCORES}" -ge  ]
then
  echo "Congratulations. ${NAME}"
elif [ "${MATH_SCORES}" -ge  ]
then
  echo "Come on ${NAME}."
else
  echo "What are you interested in? Please tell me, maybe i can help you, "${NAME}" ?"
fi;fi

echo
[web@h p]$ ./if_then_else.sh
The command requires that options have a student's name.
What's your name? :sunny
No, sunny is a teacher.
Pleae input your name,ok? sunny
My god,i think, you are bann sunny, excuse me.

What are you interested in? Please tell me, maybe i can help you, sunny ?

语句体，以fi结束。

　　利用选择语句判断变量获取成功与否

JAVA_PATH=`which java >/dev/null`
if [ "x$JAVA_PATH" != "x" ]; then
    JAVA_PATH=`dirname $JAVA_PATH >/dev/null`
    JRE_HOME=`dirname $JAVA_PATH >/dev/null`
fi

1.2.case 语句

　　双分号不能少；跟if一样，语句体也需要结束符。

　　找工作时，根据应聘岗位不同，给出不同应征者相应的联系人信息。

#!/bin/bash

echo -e "\v\tRecruitment Announcement"
echo "Are you ready to apply for any job?"
echo "1 accounting"
echo "2 cashier"
echo "3 secretary"
echo -e "\vPlease enter a number to select the corresponding positions."

read NUM
case $NUM in
  )
    printf "call mr wang. number is 1124\n"
    ;;
  )
    printf "call miss li. number is 1233.\n"
    ;;
  )
    printf "call miss ji. number is 1367.\n"
    ;;
  *)
    printf "If you want to make a lot of money, to be a seller. call 1498.\n"
    ;;
esac

　　在输出交互信息时，使用了echo命令。当要格式化输出时，需要来回调试。这里仅仅为了熟悉下case语句的语法，更好的方法在“cat”博文里重新实现。

　　使用case语句，处理坐标移动的结果。

#!/bin/bash

echo $(date)
X1=
Y1=

echo "L - turn left"
echo "R - turn right"
echo "U - turn up"
echo "D - turn down"
read INS

case $INS in
  L)
    X1=$[${X1}-]
    ;;
  R)
    X1=$[${X1}+]
    ;;
  U)
    Y1=$[${Y1}+]
    ;;
  D)
    Y1=$[${Y1}-]
    ;;
  [[:lower:]])
    printf "Uppers, please.\n"
    ;;
  *)
    ;;
esac

echo "x = ${X1} y = ${Y1}"

　　输出脚本的帮助信息：

case "$1" in
    "")
        run_it
        ;;
    -r|--read)
        read_it
        ;;
    -v|--version)
        display_version
        ;;
    --clear)
        clear_TMPFILE
        ;;
    -h|--help)
        display_help
        ;;
    *)
        echo "findTom -h"
        display_help
        ;;
esac

如果“"-v|--version"”，以双引号表示，会出现意外。要是想用，就该这么写：“"-v"|"--version"”。

1.3.通过辑判断实现条件测试

[view@file donatello]$ [  -gt  ] && echo "true " || echo "false "
false
[view@file donatello]$ [ !  -gt  ] && echo "true " || echo "false "
true

[work@file donatello]$  [ !  -gt  ] && ( echo -n "true, "; echo "exit 0" ) || ( echo -n "false, "; echo "exit 1" )
true, exit
[work@file donatello]$  [  -gt  ] && ( echo -n "true, "; echo "exit 0" ) || ( echo -n "false, "; echo "exit 1" )
false, exit 

2.循环

---

2.1.for循环

　　语法格式：

for　name[ [in [words…] ] ; ] do　commands; done
for ((expr1;expr2;expr3)) ; do　commands; done

[web@h p]$ ls >> java.dir
[web@h p]$ cat java.sh
#!/bin/bash

for i in $(cat java.dir)
do
  echo $i
done

计算1加到10

#!/bin/bash

declare -i sum=
for i in {..}
do
        sum=$((sum+i))
done

echo sum = $sum

#!/bin/bash

sum=
for i in $(seq  )
do
        sum=$((sum+i))
done

echo sum = $sum

for 语句不带列表，就从命令行获取列表信息

[web@h p]$ cat t1.sh
#!/bin/bash

for i
do
  echo $i
done
[web@h p]$ sh t1.sh ls
ls
[web@h p]$ sh t1.sh `ls`

类C风格（体现在“for”语句中、以及循环体中；变量不需要“$”符号）

#!/bin/bash

SUM=
MAX=
MIN=

for ((i=MIN; i<= MAX; i++))
do
  SUM=$[SUM+i]
done

echo "From ${MIN} add to ${MAX} is $SUM."

2.2.循环until、while

　　条件判断时如果涉及了命令的返回值，该值不管返回了0还是1之类，都需要跟数字比较来控制程序的运行。

#语法

until test-commands; do　consequent-commands; done
while test-commands; do　consequent-commands; done

　　while循环是条件满足时开始执行；until循环是条件不满足时开始循环。

　　举个例子，条件为假时，才能执行循环体语句：

#!/bin/bash
until false
do
        echo -n '-'
        sleep
        echo -e -n '\b\'
        sleep
        echo -e -n '\b-'
        sleep
        echo -e -n '\b/'
        sleep
        echo -e -n '\b*'
done

　　若是换作了条件满足时执行循环体语句的情况，就可以选择while语句。

　　while还可以直接读取文件，在done语句处“done < /path/to/file”。查看系统默认挂载的特殊文件系统：

#!/bin/bash
#

while read LINE; do
        echo $LINE | grep -v dev &> /dev/null
        if [ $? -eq  ]; then
                echo $LINE | awk '{print $1}' | grep -v boot
        fi
done < /etc/fstab

---

bash脚本调试

　　检查脚本语法、调试执行脚本

$ bash -n adduser.sh
$ bash -x adduser.sh

　　shell脚本追踪

　　在测试脚本时，可以使用set命令进行运行时的追踪。在脚本中加入一行“set -x”；以“+”开头的行，就是获得的追踪内容（程序的执行过程）。

[root@right mag]# cat tes.sh
#!/bin/bash

set -x
read -p "How old are you? " answer
if [ $answer == "" ]; then
    echo "Yes, very good."
else
    echo "No, i don't want say anyting."
fi

exit
[root@right mag]# ./tes.sh
+ read -p 'How old are you? ' answer
How old are you?
+ '['  ==  ']'
+ echo 'Yes, very good.'
Yes, very good.
+ exit
[root@right mag]# ./tes.sh
+ read -p 'How old are you? ' answer
How old are you?
+ '['  ==  ']'
+ echo 'No, i don'\''t want say anyting.'
No, i don't want say anyting.
+ exit 

　　看看没有追踪的执行过程：

[root@right mag]# ./tes.sh
How old are you?
No, i don't want say anyting.