bash编程

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变量，数组 $$ pid $? last returned value ${} 和 $() read mktemp trap iptables sed

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声明一个数组

declare -a array。 比如：

declare -a badstrings=("Failed password for invalid user"
                "input_userauth_request: invalid user"
                "pam_unix(sshd:auth): check pass; user unknown"
                "input_userauth_request: invalid user"
                "does not map back to the address"
                "pam_unix(sshd:auth): authentication failure"
                "input_userauth_request: invalid user"
                "reverse mapping checking getaddrinfo for"
                "input_userauth_request: invalid user"
                )

获取数组长度

${#array[@]} 或者 ${#array[*]}

按索引查找

array[n] 其中n为从0到 ${#array[*]} - 1的整数

遍历数组

filename=(`ls`)
for var in ${filename[@]};do
echo $var
done

数组赋值

array[n] = 'modified' 其中n为从0到 ${#array[*]} - 1的整数

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read

Bash 内置的从标准输入读取数据的接口。

  - 从键盘输入中读取数据:
    read variable

  - 从键盘输入中读取数据，并转化为数组:
    read -a array

  - 限制最大允许读取的字节数为character_count:
    read -n character_count variable

  - 使用其他分隔符，而不是默认的换行:
    read -d new_delimiter variable

  - 不转义:
    read -r variable

  - 展示prompt:
    read -p "Enter your input here: " variable

  - 静默模式:
    read -s variable

例子：

FILE=/etc/passwd
while read line
do
    # store field 1
    F1=$(echo $line|cut -d$FS -f1)
    # store field 2
    F2=$(echo $line|cut -d$FS -f6)
    # store field
    F3=$(echo $line|cut -d$FS -f7)
    echo "User \"$F1\" home directory is $F2 and login shell is $F3"
done < $FILE

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iptables

配置防火墙规则。

  - View chains, rules, and packet/byte counters for all tables:
    sudo iptables -vnL

  - Set chain policy rule:
    sudo iptables -P chain rule

  - Append rule to chain policy for IP:
    sudo iptables -A chain -s ip -j rule

  - Append rule to chain policy for IP considering protocol and port:
    sudo iptables -A chain -s ip -p protocol --dport port -j rule

  - Delete chain rule:
    sudo iptables -D chain rule_line_number

  - Save iptables configuration of a given table to a file:
    sudo iptables-save -t tablename > path/to/iptables_file

  - Restore iptables configuration from a file:
    sudo iptables-restore < path/to/iptables_file

常见的rule有DROP 和 ACCEPT，分别表示黑名单和白名单。 更多参考：https://www.thegeekstuff.com/2011/06/iptables-rules-examples/

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sed

脚本化操作文本。

  - Replace the first occurrence of a string in a file, and print the result:
    sed 's/find/replace/' filename

  - Replace all occurrences of an extended regular expression in a file:
    sed -E 's/regex/replace/g' filename

  - Replace all occurrences of a string in a file, overwriting the file (i.e. in-place):
    sed -i '' 's/find/replace/g' filename

  - Replace only on lines matching the line pattern:
    sed '/line_pattern/s/find/replace/' filename

  - Print only text between n-th line till the next empty line:
    sed -n 'line_number,/^$/p' filename

  - Apply multiple find-replace expressions to a file:
    sed -e 's/find/replace/' -e 's/find/replace/' filename

  - Replace separator / by any other character not used in the find or replace patterns, e.g., #:
    sed 's#find#replace#' filename

比如：sed -r 's/\s+/,/' 是变成类似CSV的格式。