我喜欢的一句话
the only way to really learn scripting is to write scripts
学习脚本的唯一方法就是写脚本
更好的命令行参数检测
E_WRONGARGS=85 # Non-numerical argument (bad argument format).
41 #
42 # case "$1" in
43 # "" ) lines=50;;
44 # *[!0-9]*) echo "Usage: `basename $0` lines-to-cleanup";
参数中间没有数字，无效参数
45 # exit $E_WRONGARGS;;
46 # * ) lines=$1;;
47 # esac
更有效的目录检测
3 # cd /var/log || {
64 # echo "Cannot change to necessary directory." >&2
65 # exit $E_XCD;
66 # }
#!/bin/sh invokes the default shell interpreter, which
defaults to /bin/bash on a Linux machine.
#!/bin/bash 叫做sha-bang magic number
测试调用的参数数量是否正确
1 E_WRONG_ARGS=85
2 script_parameters="-a -h -m -z"
3 # -a = all, -h = help, etc.
4
5 if [ $# -ne $Number_of_expected_args ]
6 then
7 echo "Usage: `basename $0` $script_parameters"
8 # `basename $0` is the script‘s filename.
9 exit $E_WRONG_ARGS
10 fi
调用脚本
bash scriptname
chmod 555 scriptname (gives everyone read/execute permission) [9]
or
chmod +rx scriptname (gives everyone read/execute permission)
chmod u+rx scriptname (gives only the script owner read/execute permission)
./scriptname
1 #!/bin/rm
2 # Self-deleting script.
echo "This line will never print (betcha!)."
这是一个自杀的脚本
# Nothing much seems to happen when you run this...
except that the file disappears.
将文档改成#!/bin/more 并且添加可执行权限
结果就是自列表文档 类似cat XX | more
特殊字符
# 注释 ，行开头#注释，不被执行，取消语法检测
在引号和逃逸符里面不是注释
6 echo ${PATH#*:} # Parameter substitution, not a comment.
7 echo $(( 2#101011 )) # Base conversion, not a comment.
; 命令分隔符
1 echo hello; echo there
;; case选项分隔符
1 case "$variable" in
2 abc) echo "\$variable = abc" ;;
. 相当于source 刷新配置文件，重新加载
作为文件名称的一部分，隐藏文件
相当于当前目录，..相当于上级目录
在正则表达式中匹配单个字符
" 部分引用或弱引用，抑制大部分的特殊字符
‘ 强引用，抑制所有的特殊字符
, 链接一串算数操作，只返回最后的结果
1 let "t2 = ((a = 9, 15 / 3))"
2 # Set "a = 9" and "t2 = 15 / 3"
链接字符串
1 for file in /{,usr/}bin/*calc
2 # ^ Find all executable files ending in "calc"
3 #+ in /bin and /usr/bin directories.
\ 逃逸字符，表达字符字面值的意思
/ 文件路径分隔符
` 输出命令结果给变量
： 不做任何事，占位符
：>将文件长度改为0，并且不改变权限，不在则创建
: > data.xxx # File "data.xxx" now empty.
Same effect as cat /dev/null >data.xxx
也可作为域分隔符 在/etcpasswd中
！ 转换退出状态或者测试的感觉
change the sense of equal ( = ) to not-equal ( != )
也可调用命令历史
* 通配
在正则中匹配0个或多个字符
在算数中 单个表示乘号 两个表示阶乘
？ 在双括号中，？作为三元操作符
(( var0 = var1<98?9:21 ))
在通配和正则中代表单个字符
$ 变量
跟变量名表示变量的值
在正则中表示一行的结尾
[email protected] $* 位置参数
$? 退出状态的变量
$$ 表示当前脚本的进程ID
() 命令组,括号中的命令是子shell，对外面不可见
数组初始化
1 Array=(element1 element2 element3)
{} 命令扩展
8 cp file22.{txt,backup}
9 # Copies "file22.txt" to "file22.backup"
----
echo {file1,file2}\ :{\ A," B",‘ C‘}
file1 : A file1 : B file1 : C file2 : A file2 : B
file2 : C
----
echo {a..z} # a b c d e f g h i j k l m n o p q r s t u v w x y z
----
8 base64_charset=( {A..Z} {a..z} {0..9} + / = )
9 # Initializing an array, using extended brace expansion.
表示代码块
对脚本其他地方可见，非子shell
1 a=123
2 { a=321; }
3 echo "a = $a" # a = 321 (value inside code block)
也可作为占位符
ls . | xargs -i -t cp ./{} $1
[] 表示测试
数组元素
1 Array[1]=slot_1
2 echo ${Array[1]}
表示字符范围
$(()) 整数表达式
1 a=3
2 b=7
3
4 echo $(($a+$b)) # 10
> &> >& >> < <> 重定向操作符
< > 作为ASCII码比较
\<,\> 单词锚定
| 管道
Passes the output (stdout) of a previous command to the input (stdin) of the next one
管道作为子shell运行，因此不能修改父shell的变量
>| 强制重定向
|| 逻辑或
& 后台运行job
&& 逻辑与
^ 行头部匹配
备份当前目录最近24小时内修改的文件
1 #!/bin/bash
2
3 # Backs up all files in current directory modified within last 24 hours
4 #+ in a "tarball" (tarred and gzipped file).
5
6 BACKUPFILE=backup-$(date +%m-%d-%Y)
7 # Embeds date in backup filename.
8 # Thanks, Joshua Tschida, for the idea.
9 archive=${1:-$BACKUPFILE}
10 # If no backup-archive filename specified on command-line,
11 #+ it will default to "backup-MM-DD-YYYY.tar.gz."
12
13 tar cvf - `find . -mtime -1 -type f -print` > $archive.tar
14 gzip $archive.tar
15 echo "Directory $PWD backed up in archive file \"$archive.tar.gz\"."
16
17
18 # Stephane Chazelas points out that the above code will fail
19 #+ if there are too many files found
20 #+ or if any filenames contain blank characters.
21
22 # He suggests the following alternatives:
23 # -------------------------------------------------------------------
24 # find . -mtime -1 -type f -print0 | xargs -0 tar rvf "$archive.tar"
25 # using the GNU version of "find".
26
27
28 # find . -mtime -1 -type f -exec tar rvf "$archive.tar" ‘{}‘ \;
29 # portable to other UNIX flavors, but much slower.
30 # -------------------------------------------------------------------
31
32
33 exit 0