Linux Series - SED Utility/Package - 3. Printing Lines

 In the previous example, you saw that input passed into sed with substitute operation would print the results directly to standard output. 

Let’s explore sed’s explicit print command, which you specify by using the option 'p'.

Again, we are using the same test.txt file as an input to print the lines. To do so, run the command "sed 'p' test.txt".

You’ll see line of the test.txt file printed twice.  This is because sed automatically prints each line by default, and then you’ve told it to print lines explicitly with the “p” option, so you get each line printed twice.

You can clean up the results by passing the -n option to sed, which suppresses the automatic printing.

We now are back to printing each line once.

Now, let us update few more lines in test.txt file to explain how print line works in multiple ways. The test.txt file is updated and here is the content of the file.

Printing particular line from a file

Run the command "sed -n '1p' test.txt". This will print the first line from the file. Here '1' represents the number of the line we would to like retrieve.

Incase, if you want to print the last line of the file, you need to run the command "sed -n '$p' test.txt" . Here $ represents the last line.

Printing range of lines  from a file

Run the command "sed -n '1,4p' test.txt". This will print the first line to fourth line from the file. Here '1 ' represents the starting number of the line and '4' represents ending number of line we would to like retrieve.

Incase, if you want to print  from third line to the last line of the file, you need to run the command "sed -n '3,$p' test.txt"

Printing few lines (ranges) from a file

Run the command "sed -n '2,+3p' test.txt". This will print the second line to fifth line from the file. Here '2 ' represents the starting number of the line and '+3' represents three lines from second line (2+3 =5) we would to like retrieve.

Run the command "sed -n '1~3p' test.txt". This will print the first line and fourth line and so on till the file exhausted. Here '1 ' represents the starting number of the line and '3' represents three lines  jump from first line we would to like retrieve.

For instance, '50~5p' matches line number 50, 55, 60, 65, and so on until file data exhausted. 

Printing lines based on the pattern from a file

A  pattern range can be a simple text or a complex regular expression. Let us take an example. I have a file called "Rahul.txt" and I would like to print the lines which contains the text "cricket". 

Run the command "sed -n '/cricket/p' Rahul.txt"

Just to let you know that this will not look exactly "cricket" word alone and it will print "cricket*" as well. * represents any characters after cricket. Let us see another example with the same "Rahul.txt" file. This time we can look for "Depend" word from the file.

As you see the result prints the line which has "Dependable".

Printing few lines (ranges)  based on the pattern from a file

Let us see an example with the same "Rahul.txt" file. This time, we can look from the line which  has "Karnataka" word to end of the file.  To do so, run the command

"sed -n '/Karnataka/,$p' Rahul.txt". Remember this command will always consider for the first match and then process till last line as its mentioned $.

Let us see another example with the same "Rahul.txt" file. This time, we can look from the line which  has "Karnataka" word and retrieve three lines after that.  To do so, run the command

"sed -n '/Karnataka/,+3p' Rahul.txt"

Let us see another example with the same "Rahul.txt" file. This time, we can look from the line which  has "Karnataka" word and retrieve until tenth line.  To do so, run the command

"sed -n '/Karnataka/,10p' Rahul.txt"

Let us see another example with the same "Rahul.txt" file. This time, we can look from the line which  has "gentleman" word and retrieve until another line contains "Karnataka"  .  To do so, run the command

"sed -n '/gentleman/, /Karnataka/p' Rahul.txt"

Hope you now understand how sed prints the line from the file based on the given  condition 😀.