2: Working with Files

Creating Files

touch

• used to create any type of file with zero size

touch demo.txt

 The creation of files can be done in different ways, one of them is using redirection.

ls >

Let's take the output of our previous ls command and save it in a text file. 

This can be done by using ">" after the command and adding the name of the file to write to, as follows:

ls > ls_output.txt

With this command, the output of the ls command is redirected to the text file.

 

Viewing files

cat

We can view the content of the file on the terminal by using the command:

The following command allows you to see what your operating system is

• cat file _name:  Displays content of a file (concatenate)

  cat ls_output.txt
  

cat does not support keyboard scrolling

 cat /etc/os-release

more

displays content of a file one page at a time 

echo

We can display some text that we type into the command line, not necessarily reading it from a file, by using the command:

• echo "text":  printing text on the terminal

echo "display new text"

The echo command prints its parameters 

 

We can also create text files using the echo command, by redirecting the text in the parameters, as follows:

echo "display new text 1" > test_file_1
echo "display new text 2" > test_file_2

We can check the test files that we created again using the ls command. The output would be:

 

Note

To use echo and create a file with multiple-line content, use \n when a new line is needed:

Example:

echo "123 \n456 \n789" > new_file_txt

 

head

To display the beginning of a file, we use the command:

• head   file_name :  Displays the beginning (head) of a file

head -n1 ls_output.txt       (displays first 1 line of ls_output.txt)
head -n2 ls_output.txt       (displays first 2 lines of ls_output.txt)

Output:

 

If we want to scroll up/down arrows to look at the file content, we use the command:

• less 

less /tmp/test/ls_output.txt

tail

To display the end of a file, we use the command:

• tail   file_name :

  tail /tmp/test/ls_output.txt
  

• To display a certain number of lines (for example 20 lines) we can add the option -n20 as follows:

tail -n20 /tmp/test/ls_output.txt   

• To display new lines in real-time, we can add the option -f as follows:

tail -f /tmp/test/ls_output.txt          

 

Operations on files

find

find a file

find /home/path -iname filename.extension
find /home/path -filename *.extension

mv - moving files

Let's move one of the test files that we created previously to one of our subdirectories. This is done b the command:

• mv    file_name    directory_name : move a file to a directory

mv test_file_1.txt subdir1

We can check that the file moved to the desired directory by using the ls command. The output would be:

 

grep - finding content in a file

To find a string in a file, we use the command:

• grep   string_content   file_name :  Global Regular Expression Print 

Output:

 

Modifying file content

If we want to modify the content of a file on the terminal, we can use nano through the command:

• nano   file_name : 

  nano /tmp/test/test_file_2.txt
  

Note

Using the nano editor, we use CTRL+O+Enter and CTRL+X to save changes

 

Deleting a file

• rm    file_name :  remove

  rm test_file_2.txt
  rm -rf /tmp/test/subdir1
  

Note

To delete a folder, use -rf (recursive force)

 

Substituting content of a file

For command testing purposes, let's create a new file with the following text:

echo "Course number 1, course number 2, course number 3, course number 4"  > test_file_3.txt

To find and replace something in a file, we can use the command: 

• sed  'options'  input_file_name

sed 's/course/class/' test_file_3.txt

If we now check the content of the file using cat:

cat test_file_3.txt

Output:

Every word "course" is replaced by the word "class":

"Class number 1, class number 2, class number 3, class number 4"

 

screenshot to be added

 

Sorting file content

Let's create a new file entitled file_to_sort.txt with the following example content:

echo "Amanda \nMelody \nRosa \nJohn \nCaleb \nRick" > file_to_sort.txt

To check the content of the file, we use the "cat" command.

Output:

to be replaced

To sort the content of the file, we use the command: 

• sort

sort file_to_sort.txt

Output:

to be replaced

By using the sort command, the result is displayed only but not saved. To capture the result we need to store it. For this purpose, the -o option is used.

To save the sorted content in the same file:

sort -o file_to_sort.txt file_to_sort.txt 

To save the sorted content in a separate file different from the original one:

sort -o new_file_to_sort.txt file_to_sort.txt

 

Sorting for Column Number

Sorting can be done with file content that has more than one column. Let's create a new text file entitled "file_to_sort_columns.txt" in which there are names and ages (2 columns).

Let's organize them in ascending order. For that, we use the keyword –k in the command and –n for numerical sorting (Since there are two columns, 2 is used with -n)

sort –k 2n file_to_sort_columns.txt

Output:

to be added 

 

Checking the Sorting of the file

If we want to check if the file was sorted, we can display the file content using the cat command:

cat file_to_sort_columns.txt

Output:

to be added 

 

Removing duplicates

If there are repeated words in the file, we can use the sort command with -u option to remove the duplicate, as follows:

sort -u file_to_sort_columns.txt

Now, we can see that the data is sorted and the repeated items are removed from the output.

to be added 

 

 Sorting in Reverse Order

We can sort the file in reverse order (descending order by default) sort by using -R option with the sort command.

sort -R file_to_sort_columns.txt

Output:

to be added 

 

Other useful commands

wc – line count, char count, word count, max line length

unzip – unzip a zip file

gunzip – unzip a gz file

bunzip – unzip a bz file

tar – extract files from a tar archive, (tar file)

zip

sudo zip -r soundfiles samples/

 

 

 

 

 

• tree:  shows tree in directories

  tree
  

• uniq

filters out duplicate lines in a test file

 

wc:  word count

wc -l line count