SED stands for stream editor. You can use it in Linux or UNIX and as a command line terminal or you can run your Linux command through SED. You can used it for text substitution for finding and replacing. SED also perform a lot of manipulations on the text like searching, deletion, and insertion. You can edit the file using SED without opening the files. SED also provides a better way for using the arithmetic operation and their manipulation.

In this article we will discuss about the use of SED. How to use the GNU SED with different commands and their examples.

An Overview of SED

There are three steps in SED for performing a task:

  • Red data or command from input stream
  • Execute and run this commands
  • Show the results on output stream

Options in SED

With SED commands you can use different options that perform some specific tasks against that commands:

“ –i ” This option helps to edit the source files

“ –e ” If you want to run multiple SED commands with a single command than –e is very useful.

“ –n ” This option used for default output.

“ –f ” This option help to run a SED script files.

SED commands with Special Characters

SED also provide some special characters. You can use these characters for different purposes. Some special characters and their description is given below:

“ ^ ” This character helps to find the beginning of the line.

“ $ ” The dollar sign helps for finding the end of the line.

“ . ” Dot sign find the single characters from the text.

“ * ” The steric sign find the occurrences of previous character.

How to use SED with Commands and their Examples

Similar to Linux commands SED has its own commands and there is a lot of commands are available in SED. Now we are focusing on different SED Commands with examples:

Get the Lines from File with Given Range

# sed -n ‘ 8, 12p ‘ filename.txt

The above command return the lines from 8 to 12 from filename.txt.

Get All Lines except a given Range

# sed ‘ 15, 25d ‘ filename.txt

This command will return all the text from filename except lines from 15 to 25.

The use of “-e” option

# sed -n -e ‘ 4, 8p ‘ -e ‘ 12, 16p’ filename.txt

This command will the lines from 4 to 8 and also return from 12 to 16 from whole text in filename.txt.

Insert Blank Spaces in Files

SED provides a command for inserting blank spaces in file text.

# sed G filename.txt

Search data and Replace it

You can find some text or data from file in SED and replace that data using command:

# sed ‘ s/John/William/g’ filename.txt

In this command first SED will find the John and then replace it with William in all over the file.

Add a complete Line After or before

# sed ‘/John/a ‘ Add this new line after matching ‘ ‘ filename.txt

This command work similar above command first search keyword then add given new line after that keyword.

What is the use of sed command?

SED command in UNIX is stands for stream editor and it can perform lot’s of function on file like, searching, find and replace, insertion or deletion. Though most common use of SED command in UNIX is for substitution or for find and replace.

How do I run a sed script?

There are two ways of running sed:
  1. you can give the commands on the command line: sed ‘s/yes/done/’ file. If you want to use several commands, you have to use the -e option:
  2. it is also possible to place the commands in a seperate file: sed -f sedsrc file. where sedsrc contains the necessary commands.

How do you insert a line using sed?

sed – Inserting Lines in a File
  1. Insert line using the Line number. This will insert the line before the line at line number ‘N’. Syntax: sed ‘N i <LINE-TO-BE-ADDED>’ FILE.txt Example:
  2. Insert lines using Regular expression. This will insert the line before every line where pattern match is found. Syntax:

How do you use SED in Awk?

3 Answers
  1. BEGIN{FS=OFS=” : “} use : as input/output field separator.
  2. gsub(/ /,”_”,$2) replace all spaces with _ only for second field.
  3. Similarly other substitutions as required.
  4. 1 at end of command is idiomatic way to print the line, includes any changes made.
  5. See also awk save modifications in place.

How do I replace text in awk?

The first task in our list is a substitute, which we write as sub. Sub directs awk to find all occurrences of OLD_TERM and replace them with NEW_TERM. Our next instruction directs awk to print the output to the standard output stream; the console. Finally, we have the name of the file that awk will be working on.

Can we use awk inside awk?

You can even do the numeric sort inside awk, but it’s too much work for nothing.

What awk command does?

Awk is a scripting language used for manipulating data and generating reports. The awk command programming language requires no compiling, and allows the user to use variables, numeric functions, string functions, and logical operators. Awk is mostly used for pattern scanning and processing.

What does AWK mean?

(Entry 1 of 2) 1 obsolete : turned or done the wrong way. 2 obsolete : perverse. 3 obsolete : awkward, clumsy.

What is difference between sed and awk?

The main difference between sed and awk is that sed is a command utility that works with streams of characters for searching, filtering and text processing while awk more powerful and robust than sed with sophisticated programming constructs such as if/else, while, do/while etc.

How do I write an awk script?

#!/usr/bin/awk -f BEGIN { printf “%s\n”,”Writing my first Awk executable script!” }

Explaining the line above:

  1. #! – referred to as Shebang, which specifies an interpreter for the instructions in a script.
  2. /usr/bin/awk – is the interpreter.
  3. -f – interpreter option, used to read a program file.

What does $0 represent in awk?

$0 signifies the entire record. For example, $0 represents the value of the entire record the AWK program read on standard input. In AWK, the $ means “field” and is not a trigger for parameter expansion as it is in the shell. Our example program consists of a single action with no pattern present.

What does print $0 mean?

When lines containing ‘ li ‘ are found, they are printed because ‘ print $0 ‘ means print the current line. (Just ‘ print ‘ by itself means the same thing, so we could have written that instead.) You will notice that slashes (‘ / ‘) surround the string ‘ li ‘ in the awk program.

What is awk and sed?

Awk, like Sed, is a programming language designed for dealing with large bodies of text. But while Sed is used to process and modify text, Awk is mostly used as a tool for analysis and reporting. Awk works by reading a text file or input stream one line at a time.

What is a $1 awk?

With awk , $1 refers to the first field of the current input record and $0 refers to the complete input record, while in the shell, $1 refers to the first positional parameter (usually the first argument on the command line of a script or function) and $0 usually refers to the name of the current shell or shell script.

What AWK $2?

awk splits its input lines on white space (by default) and saves each field as $1 , $2 etc. So, the actual expression you are running means: read each input line, add 0.45 to the value of the first field and then print that field as well as the second and third one.

What is print $1?

I. If you notice awk ‘print $1‘ prints first word of each line. If you use $3, it will print 3rd word of each line.

How do you sum in awk?

2 Answers. The -F’,’ tells awk that the field separator for the input is a comma. The {sum+=$4;} adds the value of the 4th column to a running total. The END{print sum;} tells awk to print the contents of sum after all lines are read.