Linux Classroom Series – 19/Sept/2020

Extended grep (grep -E or EGREP)

• Write a extended regex with alternations
• Lets look for examples
• Grep Options
  1. -b
  2. -c
  3. -h
  4. -i
  5. -l
  6. -n
  7. -s
  8. -v
  9. -w

Sed

• This is streamline, non interactive editor
• version of sed
• File used in the class Refer here for sales.csv

wget https://gist.githubusercontent.com/shaikkhajaibrahim/8eb405804c97dba868ee9e359109871d/raw/901edf320164af623eba04f5affbbc4ab1e93038/sales.csv

• Sed cheatsheet Refer Here or use any cheatsheet of your choice

• Sed Commands:

  • a\
  • b label
  • c\
  • d
  • D
  • i\
  • h
  • H
  • g
  • G
  • l
  • n
  • N
  • P
  • q
  • w
  • W
  • s/re/string/

• Error messages:

  1. Unknown command

  sed '1,3v ' sales.csv
  

• Examples

• Write a sed command to print

  • all the records having Libya
  • Replace Libya with UAE
  • Insert a line for all the records which have Canada with any text
  • Insert a line at the end of the file

AWK

• AWK is programming language for manipulating data and generating reports.
• AWK format

awk 'pattern' filename
awk '{action}' filename
awk 'pattern' '{action}' filename

• Search for any cheat sheet of awk Refer here

Shell scripts

• How to deal with named arguments

./installjava.sh --package-name openjdk8-jdk

• Lets understand an important operator called as shift

  • When the run shift the current positional parameters are shifted left n times default value of n is 1
  • Look at the below example

  #!/bin/bash
  
  echo "arguments passed are: $@"
  echo "total number of arguments $#"
  echo "first argument is $1"
  shift
  echo "after shift"
  
  echo "arguments passed are: $@"
  echo "total number of arguments $#"
  echo "first argument is $1"
  
  shift 2
  
  echo "after shift 2"
  echo "arguments passed are: $@"
  echo "total number of arguments $#"
  echo "first argument is $1"
  
  

  • The output of execution with various examples is

• We can use shift operator and a while loop to parse arguments

#!/bin/bash
#./calc.sh --print 1 --square 2
#./calc.sh -p 1 -s 2

while [[ $# -gt 0]]
do
    key="$1"
    case $key in 
        -p|--print)
        echo "$2"
        shift 2
        ;;
        -s| --square)
            number="$2"
            echo $((number * number))
        shift 2
        ;;
    esac
done

• Simple square and cube calculator

#!/bin/bash

while getopts "s:c:" option;
do 
    case "$option" in
        s)
            value=$OPTARG
            echo "$((value * value))"
            ;;
        c)
            value=$OPTARG
            echo "$((value * value * value))"
            ;;

    esac
done

• Exercise: Extend this script to display help when user passes -h and also support long options