******************************
linux运维常用命令
******************************

查看具体端口
============================

.. code-block:: console

    $ netstat -tnlp |grep 9100

在后台运行进程
==============================

.. code-block:: console

    $ nohup ./agent_manager >agent_manager.log 2>&1 &

停止脚本stop_updater.sh的内容

.. code-block:: bash

    #!/bin/bash
    kill `ps -ef | grep agent_manager | grep -v grep | awk '{print $2}'`
    kill `ps -ef | grep node_exporter | grep -v grep | awk '{print $2}'`

shell
================================

if.sh
--------------------

.. code-block:: shell

    #!/bin/bash

    # testing the if statement
    if pwd # 如果该命令的退出状态码为0, 那么位于then部分的命令就会被执行。
    then
      echo "it worked"
    fi

    # testing multiple commands in the then block
    # 在then语句中列出多条命令
    testuser=christine
    if grep $testuser /etc/passwd
    then
      echo "This is my first command in the then block."
      echo "This is my second command in the then block."
      echo "I can event put in other commands besides echo:"
      ls /home/$testuser/*.sh
    fi
    echo "We are outside the if statement"

    # testing the else section
    # if ... then ... else
    testuser=NoSuchUser
    #
    if grep $testuser /etc/passwd
    then
      echo "Thescript files in the home directory of $testuser are:"
      ls /home/$testuser/*.sh
      echo
    else
      echo "The user $testuser dose not exist on this system."
      echo
    fi
    echo "We are outside the if statement"

    # testing nested ifs - using elif
    # elif语句
    if grep $testuser /etc/passwd
    then
      echo "The user $testuser account exists on this system."
      echo
    elif ls -d /home/$testuser/
     then
       echo "The user $testuser has a directory,"
       echo "even though $testuser doesn't have an account."
      else
        echo "The user $testuser does not exist on his system"
        echo "and no directory exists for the $testuser"
    fi
    echo "We are outside the nested if statements."

mydate.sh
--------------------

.. code-block:: shell

    #!/bin/bash

    # 代码来自<<Linux命令行于shell脚本编程大全(第4版)>> 11.9
    # calculate the number of days between two dates
    date1="Jan 1, 2020"
    date2="May 1, 2020"

    # 原文是使用expr命令，但这个是过时的语法，参阅: https://github.com/koalaman/shellcheck/wiki/SC2003
    time1=$(date -d "$date1" +%s)
    time2=$(date -d "$date2" +%s)

    diff=$((time2 - time1))
    secondsinday=$((24 * 60 * 60))
    days=$((diff / secondsinday))

    echo "The difference between $date2 and $date1 is $days days"