#!/bin/bash
cd /usr/local
ls
cd -

語法(syntax)

1. 自定義語法 (Custom syntax)

#!/bin/bash
var1=hello
var2=world

echo $var1 $var2
echo $USER `s home is $HOME

2. 系統語法 (system syntax)

#!/bin/bash
echo $HOME
echo $USER

3. 返回值語法(return value syntax)

#!/bin/bash
dt=`date`
dirs=`ls /usr/local`

echo $dt
echo $dirs

表示式(expression)

1. 命令表示式(command expression)

#!/bin/bash
if mkdir test
then
  echo create dir success
else
  echo failed
fi

2. 數學表示式(math expression)

[ $var1 -gt/-lt/-eq/-ge/-le/-ne $var2 ]

-gt  >
-lt  <
-ge  >=
-le  <=
-eq  =
-ne  !=

#!/bin/bash

var1=2
var2=3
var3=$[ $var1 + $var2 ]

if [ $var1 -gt $var3 ]
then
 

  echo $var1 is bigger then $var3
else
  echo $var1 is smaller then $var3
fi

3. 字串表示式(string expression)

判斷字串是否一致 [ string1 =/!= string2 ]

#!/bin/bash
var1=abc
var2=def

if [ $var1 = $var2]
then
  echo $var1 is $var2
else
  echo different
fi

4. 檔案判斷表示式(File judgement expression)

1. [ -d/-f/-e/-r/-w/-x filename ] 檔案判斷對應屬性如下:

-d is dir
-f is file
-e is exists
-r is readable
-w is writeable
-x is excuteable

2. 檔案判斷 [ file1 -nt/ot file2 ]

判斷file1比file2 新/舊

• -nt file1 is newer
• -ot file1 is older

if [-d ./test]
then 
  mkdir test
else
  echo dir2 is not exists 
fi

控制結構(control structure)

if

#!/bin/bash

if expression
then 
  echo 1
  echo 2
else
  echo 3
  echo 4
fi

for

1. bash style

#!/bin/bash

for $i in value1 value2 value3
do
  echo $i
done

example:

#!/bin/bash
for i in A B C D
do 
  echo $i
done

2. C language style

#!/bin/bash

for((variable=init_value;variable<=n;variable++)))
do
  echo xxx
  echo xxx
done  

demo

#!/bin/bash

sum=0
for((i=1;i<=100;i++))
do
  sum=$[ $sum + $i ]
done

echo $sum

case

#!/bin/bash

case variable in
value1 1)
  echo 1
  ;;
value2 2)
  echo 2
  ;;
*)

echo 1
echo 2
;;

demo

#!/bin/bash
case $USER in
root)
  echo "you are super master" $USER;;
json)
  echo -n "you are " $USER;;
*)
echo sorry!
esac

匯出資料庫案例

匯出現有資料庫並刪掉7天以前的資料庫.

#!/bin/bash

filename=`date +%y%m%d`.tar.gz

if [ -f $filename ]
then
  echo "file is exists!"
else
  mysqldump -uroot -proot yii2basic > /root/test/yii2basic.sql
  tar -zcvf yii2basic.tar.gz yii2basic.sql
  mv yii2basic.tar.gz $filename
  rm -fr yii2basic.sql
  echo "mysqldump done!"
fi

old = `date -d '-7 day' + %y%m%d`

if [ -f $old.tar.gz]
then
  rm -fr ./$old.tar.gz
fi