6: File Commands

File Commands

(transclusion link)

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

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 

echo can create a new file when used with a redirect and place its content in the file

echo "insert this text into new file" > newfile.txt

find

find a file in a directory

note the "i" in iname makes it case insensitve

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

grep

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

• grep   string_content   file_name :  Global Regular Expression Print 

 

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)

less 

 

more

displays content of a file one page at a time 

mv

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

rm

 

• rm    file_name :  remove

  rm test_file_2.txt
  

sed

sed- Stream editor

sed [intial word/new word] filename

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 '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

 

sort

sort file_to_sort.txt

sort switches

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 

 

tail

Shows end of file

 

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.

a

 

wc

word count

wc switches

 

wc -l line count