Shell Automation An Introduction to

Bash Shell ScriptingAnoop John

►Shell, interpreter, POSIX

►Shell script operation

►Commands, paths, returns

►Variables, environments

►Input, output, pipes, descriptors

►Expressions, conditions, loops

►Awk, grep, sed, find, xargs

►System utils

►Examples

An Outline

►Kernel, Shell

►Interprets commands

►Command Line Interpreter / Command Line Interface

►POSIX compliance

►Sh, Bourne Again, Brian Fox, FSF

Shell, Interpreter, POSIX

►Unix

►GNU

►GPL - Four freedoms

►Use, Modify, Distribute, Modify & Redistribute

►FSF

►GNU / Linux

Free Software

►Reads input from file, string (-c), or terminal

►Breaks the input into words and operators

►Parses the tokens into simple and compound commands

►Performs the various shell expansions

►Performs any necessary redirections

►Executes the command

►Optionally waits for the command to complete and collects its exit status

Shell Operation

►Executables (ls)

►Shell commands (cd, exit, pwd)

►Return values

►Command input

►Command output

►Path

►Which

Commands

►Setting a Variable

►Environment (context)

►Script

►Eval

►Exec

►Source .

►Strings, integers, arrays

►Quoting - single, double, escaping

►Global, local

Variables & Environment

#!/bin/bash

echo “Hello World”;

name=Anoop

echo “Hello $name”

exit;

Shell Script

►Shell Scripts

►Shell Arguments

►Functions

►Function Arguments

Arguments & Functions

function log {  if [ $# ­gt 0 ]; then    echo "[$(date +"%D %T")] $@" >> $LOG_FILE    db "$@"  else     while read data    do      echo "[$(date +"%D %T")] $data" >> $LOG_FILE       db "$data"    done  fi}log “Hello World!”echo “Hello World!” | log

Shell Function

►Stdin

►Stdout

►Pipes

►Descriptors

Input & Output

►Assignment =

►Arithmetic +, -, *, /, **,

►Bitwise <<, >>, |, &, ~, ^

►Logical !, &&, ||

►Comparisons - Arithmetic -eq, -ne, -lt, -gt, le

►Comparisons - String =, !=, <, >, <=

►Filesystem - -e, -f, -d, -x

Expressions

if [[ expression ]] then

  commands;

elif [[ expression ]] then

  commands;

else

  commands;

fi

If Command

case $ANIMAL in  horse | dog | cat)     echo ­n "four"    ;;  man | kangaroo )    echo ­n "two"   ;;  *)    echo ­n "an unknown number of"   ;;esac

Case Command

for NAME [in LIST ]; do   COMMANDS; done

i=0for filename in `ls`; do   i=$(( i + 1));  printf "%­5s ­ %s\n" $i “$filename”;done;

for name in Anoop John; do   echo “Hello ${name}”;done;

For Loop

while [[ expression ]]; do   COMMANDS; done

i=0; while [[ $i ­lt 10 ]]; do  echo Counting $i;  ((i+=1));done;

while read linedo  echo $linedone < path/to/file

While Loop

►awk

►sed

►grep

►find

►xargs

►cat, less, tail, head, watch

Shell Swiss Army Knives

►ps

►top

►kill

►dmesg

►curl, wget

►chown, chmod, chgrp

►uptime, top, nice, nohup

Useful Commands

►man

►help

►command --help

►Reading scripts

►Mailing lists

►User groups

►Local community

►Search the web

Getting help

►Get GNU / Linux installed on your systems

►Start using shell

►Identify pain points in your daily operations

►Automate through scripts

►Join a mailing list

►Ask & answer questions

►Show off :-)

How to Start

►Drupal Backups

►Asianet Autologin

►Reliance Autologin

►Secure Shared Folders

Exempli Gratia

►Free Software Company

►Software Development - Drupal

►Leading Drupal Contributor from India

►FSF Contributing Member

►Free Software Support in the local market

►IT Training and FOSS Enabling

►Websites & Email Services

►IT Consultancy for Enterprises

About Zyxware

www.zyxware.cominfo@zyxware.com

9446-06-9446

Thank You!