Working With Files

Key Goals

• Working with files
• Working with links
• Analyzing text files
• Comparing text and binary files
• Modifing file content through command line
• Search for files

Section Objectives

1. Finding files:

   • which
   • find
   • locate

2. List file content:

   • less
   • cat
   • head
   • tail
   • wc

3. Working with files:

   • cp
   • mv
   • rm
   • touch
   • mkdir

4. Working with links:

   • Hard link
   • Soft link
   • inode

5. Searching in files:

   • grep

6. Editing files through the command line:

   • sed

7. Comparing files

   • diff
   • md5sum

Exercise

Note

Before starting the exercise, install the following packages

yum install -y words # Installs a file that contains a long list of words
yum install -y ntp
yum install -y tree

Finding files

1. Which binary file executes when running the lsb_release command?
2. Find the words file
3. Find the ntp.conf file
4. Copy all the pdf files located in /usr/share/doc/ to your home directory
5. Delete all the pdf files located in your home directory
6. List all the files that are bigger than 10MB inside the /boot directory
7. List all the files that are bigger than 10MB inside the /boot directory and their sizes

Reading from files

1. Scenario:

   • Display the top 27 lines of the words file.
   • Display the bottom 30 lines of the words file.

2. Which flag is needed in order to open a file using tail in a continus mode?
3. List the number of lines of the words file.

Working with files

1. Scenario:

   • Copy the /etc/hosts file to your home directory.
   • Copy it again in an interactive mode.
   • Move the file to the /tmp directory.
   • Remove the /tmp/hosts file.

2. Create the following structure inside your home directory (use wilde cards) and then delete it recursively:

Working with links

1. Explain what is an inode.
2. Explain the difference between hard link and soft link
3. How can we find the inode of a specific file?
4. Scenario: * Create tempdir directory inside your home directory. * How many hard links ~/tempdir has? * Explain why in your opinion it has that amount of hard links.
5. Scenario: * How many hard links the /etc directory has? * Explain why in your opinion it has that amount of hard links.
6. Scenario: * Create tempfile1 file inside your home directory that contains the ‘Hello World’ sentance (use one command). * Create a symlink(soft link) tempfile2 file inside your home directory to tempfile1.
7. Try to create a hard link from your home directory to your kernel file that located in the /boot directory? Explain what happend and why.

Searching in files

1. Scenario:

   • Run yum list installed (it prints all the installed packages on your system)
   • Run it again but now grep only the installed packages that their name starts with ‘kernel’.
   • Run it again but now paste the output to a kernel_pack.txt file.

   • Append to the kernel_pack.txt file the following 3 lines (use: ‘echo’ and ‘>>’):

     • newline1
     • newline2
     • newline3

   • Cat the kernel_pack.txt and grep only the newlines.
   • Use only grep (without cat) to select all the lines execpt the ‘newline2’ of the kernel_pack.txt file.

2. Which alias the grep command is uses by default?

3. Scenario (note: use the words file):

   • List all the words that start with ‘io’.
   • List all the words that end with ‘ion’.
   • List all the words that start with ‘po’, end with ‘ute’ and contain 7 characters.
   • List all the words that contain five vowels in a row (vowels: a,e,i,o,u).

Editing files through the command line

1. Scenario:

   • Install the ntp package, run: yum install -y ntp
   • Copy the ntp.conf file to your home directory
   • Delete all blank lines
   • Delete all commented lines

Compering Files

1. Scenario:

   • Copy the top 10 words of the words file to a new file inside your home directory (name it file1)
   • Copy the top 9 words of the words file to a new file inside your home directory (name it file2)
   • Use diff to compare the files and examin the difference
   • Change the first 2 lines inside file1 to ‘hello’ (using vim)
   • Use diff to compare the files and examine the difference

2. Explain what is a hash of a file?
3. In which use cases would you use hash to comapre files instead of the diff command?
4. Use the md5sum command to calculate the hash of the /etc/hosts file.