Shell知识点合集

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arr=(str1 str2 str3)
for i in ${arr[@]}
do
echo $i
done

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$# 表示命令中位置参数的数量
$* 表示所有的位置参数的内容
$? 表示命令执行后的返回的状态，用于检查上一个命令的执行是否正确。在linux中，命令退出状态为0表示命令执行正确，任何非0值的表示命令执行错误。
$$ 表示当前进程的进程号
$! 表示后台运行的最后一个进程的进程号
$0 所有参数

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-eq Equal to = Equal to   
-ne Not equal to != Not equal to
-lt Less than \< Less than (ASCII) *
-le Less than or equal to
-gt Greater than > Greater than (ASCII) *
-ge Greater than or equal to
re-directs output of one file to another.
-a file
True if file exists.
-b file
True if file exists and is a block special file.
-c file
True if file exists and is a character special file.
-d file
True if file exists and is a directory.
-e file
True if file exists.
-f file
True if file exists and is a regular file.
-g file
True if file exists and is set-group-id.
-h file
True if file exists and is a symbolic link.
-k file
True if file exists and its ``sticky'' bit is set.
-p file
True if file exists and is a named pipe (FIFO).
-r file
True if file exists and is readable.
-s file
True if file exists and has a size greater than zero.
-t fd True if file descriptor fd is open and refers to a terminal.
-u file
True if file exists and its set-user-id bit is set.
-w file
True if file exists and is writable.
-x file
True if file exists and is executable.
-G file
True if file exists and is owned by the effective group id.
-L file
True if file exists and is a symbolic link.
-N file
True if file exists and has been modified since it was last read.
-O file
True if file exists and is owned by the effective user id.
-S file
True if file exists and is a socket.
file1 -ef file2
True if file1 and file2 refer to the same device and inode numbers.
file1 -nt file2
True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
file1 -ot file2
True if file1 is older than file2, or if file2 exists and file1 does not.
-o optname
True if the shell option optname is enabled. See the list of options under the description of the -o option to the set builtin below.
-v varname
True if the shell variable varname is set (has been assigned a value).
-z string
True if the length of string is zero.
string
-n string
True if the length of string is non-zero.

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echo "content" | mail -s title 1248247511@qq.com
#mail 命令依赖 yum install mailx

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echo `expr 1 + 1`
echo "1+3","ALL" | bc

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vi help.sh
#!/bin/bash

help() {
  echo "Usage: "$0","ALL" start|stop"           //$0变量用于表示脚本文件名称
}
case "$1","ALL" in
  start)
    echo "starting..."
    ;;
  stop)
    echo "shutdown..."
    ;;
  *)
    help   //调用前面定义的help（）函数并执行其中的语句
esac

chmod a+x help.sh
./help.sh start
./help.sh restart  //参数不符合要求，输出执行帮助信息
Usage: ./help.sh start|stop

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#!/bin/bash

adder() {
  echo `expr $1 + $2`
}

adder 12 34            //将12、34作为adder函数的位置变量$1、$2
adder 56 78

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#!/bin/bash

while true;do
  
  # shell不支持浮点类型，这里只能取整数
  res=$(uptime  | awk -F'average:' '{print $2}' | awk -F',' '{print $1}' | awk -F'.' '{print $1}')
  
  if [[ $res -gt 5 ]];then
    top -d 1 -n 2 >> /tmp/log
    mpstat 1 2 >> /tmp/log
  else
    :
  fi

  sleep 1

done

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for((i=1;i<=20;i++))
do
  useradd user$i
  ran=$(echo $RANDOM | md5sum | head -c 5)
  echo "user$ran" | passwd --stdin user$i
  echo "user$i    user$ran" >> /root/user.txt
done

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for i in `ls -l /root/ | grep -v ^d |grep -v total | awk '{print $NF}'`
do
file=$(du -k /root/$i | awk '{if($1>15) print $2}')
echo $file | grep -v '^$'
done