Book Image

Linux Shell Scripting Bootcamp

By : James K Lewis
Book Image

Linux Shell Scripting Bootcamp

By: James K Lewis

Overview of this book

Linux Shell Scripting Bootcamp is all about learning the essentials of script creation, validating parameters, and checking for the existence of files and other items needed by the script. We will use scripts to explore iterative operations using loops and learn different types of loop statements, with their differences. Along with this, we will also create a numbered backup script for backup files. Further, you will get well-versed with how variables work on a Linux system and how they relate to scripts. You’ll also learn how to create and call subroutines in a script and create interactive scripts. The most important archive commands, zip and tar, are also discussed for performing backups. Later, you will dive deeper by understanding the use of wget and curl scripts and the use of checksum and file encryption in further chapters. Finally, you will learn how to debug scripts and scripting best practices that will enable you to write a great code every time! By the end of the book, you will be able to write shell scripts that can dig data from the web and process it efficiently.
Table of Contents (19 chapters)
Linux Shell Scripting Bootcamp
About the Author
About the Reviewer
Customer Feedback

Reading and writing files

This next script reads a text file and creates a copy of it:

Chapter 7 - Script 5

# 6/1/2017
echo "Chapter 7 - Script 5"

if [ $# -ne 2 ] ; then
 echo "Usage: script5 infile outfile"
 echo " Copies text file infile to outfile."
 exit 255


if [ ! -f $INFILE ] ; then
 echo "Error: File $INFILE does not exist."
 exit 100

if [ $INFILE = $OUTFILE ] ; then
 echo "Error: Cannot copy to same file."
 exit 101

rm $OUTFILE 2> /dev/null       # remove it
echo "Reading file $INFILE ..."

while IFS= read -r linevar     # use read to put line into linevar
  echo "$linevar" >> $OUTFILE  # append to file
  let x++
done < $INFILE                 # the file to use as input
echo "$x lines read."

diff $INFILE $OUTFILE          # use diff to check the output
if [ $rc -ne 0 ] ; then
 echo "Error, files do not match."
 exit 103
 echo "File $OUTFILE created."

sum $INFILE $OUTFILE           # show the checksums...