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--- linux_wiki:use_shell_scripting_to_automate_system_maintenance_tasks [2016/10/08 17:51]
billdozor
+++ linux_wiki:use_shell_scripting_to_automate_system_maintenance_tasks [2019/05/25 23:50]
@@ Line 1: / Line 1: @@
-====== Use Shell Scripting To Automate System Maintenance Tasks ======
-**General Information**
-Review of common shell scripting syntax.
-----
-====== Lab Setup ======
-The following virtual machines will be used:
-  * server1.example.com (192.168.1.150) -> Create and test some scripts
-----
-====== General Layout ======
-General bash script layout
-<code bash>
-#!/bin/bash
-echo "Hello world"
-exit 0
-</code>
-----
-====== Arguments ======
-Sending and parsing arguments to scripts.
-<code bash>
-#!/bin/bash
-echo "The first argument is: $1"
-echo "The second argument is: $2"
-echo "There are $# total arguments."
-echo "All of the arguments are: $@"
-# Loop through arguments one at a time
-for myarg in $@; do
-  echo "Argument is: $myarg"
-done
-</code>
-----
-====== Getting User Input ======
-User input with the read command
-<code bash>
-#!/bin/bash
-# If there is no argument passed, prompt for input
-if [ -z $1 ]; then
-  echo "Enter something: "
-  read myname
-else
-  # There is an argument, use that
-  myname=$1
-fi
-echo "You entered: $myname"
-exit 0
-</code>
-----
-====== Conditionals ======
-If/else conditional testing
-<code bash>
-if [ -f $1 ]; then
-  echo "Argument is a file"
-elif [ -d $1 ]; then
-  echo "Argument is a directory"
-else
-  echo "Argument is something else..."
-fi
-exit 0
-</code>
-\\
-Logical operators
-<code bash>
-# Logical AND: If first command is true, execute second command
-[ -f $1 ] && echo "This is a file"
-# Logical OR: If first command is true, do not execute second command
-[ -f $1 ] || echo "This is not a file"
-</code>
-----
-====== Loops ======
-Iterating through data.
-===== For Loops =====
-Useful for processing ranges of information.
-Specific amount of iterations
-<code bash>
-for (( count=1; count <= 100; count++ )); do
-  echo "The count is: $count"
-done
-exit 0
-</code>
-\\
-Unknown iterations through a range of data
-<code bash>
-for node in $(cat system_list.txt); do
-  ssh $node "uptime"
-done
-</code>
-\\
-Range of numbers
-<code bash>
-for number in {100..200}; do
-  ping -c 1 192.168.1.$number > /dev/null && echo "192.168.1.$number is up"
-done
-</code>
-===== While Loops =====
-While loops are useful for monitoring something or to repeat something forever and break under certain conditions.
-\\
-Loop infinitely
-<code bash>
-# Keep checking to see if a specific host is up (the first argument to the script)
-while true; do
-  ping -c 1 $1
-  # if the last command (ping) returns successful (0 exit code)
-  if [[ $? -eq 0 ]]; then
-    echo "$1 is up"
-    exit 0
-  else
-    sleep 5
-  fi
-done
-</code>
-\\
-Monitor a process
-<code bash>
-# While output results are true, go back to sleep
-while ps aux | grep $1 | grep -v grep; do
-  sleep 5
-done
-# Mail when no results from ps (process stopped)
-echo "The process($1) is no longer running." | mail -s "Process $1 stopped" root
-</code>
-===== Case Evaluation =====
-Evaluate data and provide matches for expected values.
-<code bash>
-case $1 in
-  start)
-    start_program
-  ;;
-  stop)
-    stop_program
-  ;;
-  status)
-    status_of_program
-  ;;
-  *)
-    echo "Usage: $0 (start|stop|status)"
-  ;;
-esac
-</code>
-----
-====== Debugging ======
-To debug a script, execute it with a special argument:
-<code bash>
-bash -x myscript.sh
-</code>
-  * -x -> Shows line by line what the script is doing, which allows easier debugging when it breaks
-----