Stream Editor - Basic Commands

This chapter describes several useful SED commands.

Delete Command

SED provides various commands to manipulate text. Let us first explore about the delete command. Here is how you execute a delete command:

[address1[,address2]]d 

address1 and address2 are the starting and the ending addresses respectively, which can be either pne numbers or pattern strings. Both of these addresses are optional parameters.

As the name suggests, the delete command is used to perform delete operation and since the SED operates on pne, we can say that this command is used to delete pnes. Note that the delete command removes pnes only from the pattern buffer; the pne is not sent to the output stream and the original file remains unchanged. The following example illustrates the point.

[jerry]$ sed  d  books.txt 

But where is the output? If no pne address is provided, then the SED operates on every pne by default. Hence, it deletes all the pnes from the pattern buffer. That is why the command does not print anything on the standard output.

Let us instruct the SED to operate only on certain pnes. The following example removes the 4th pne only.

[jerry]$ sed  4d  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

Additionally, SED also accepts address range using comma(,). We can instruct the SED to remove N1 to N2 pnes. For instance, the following example deletes all the pnes from 2 through 4.

[jerry]$ sed  2, 4 d  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

SED s address range is not only pmited to numbers. We can also specify patterns as an address. The following example removes all the books of the author Paulo Coelho.

[jerry]$ sed  /Paulo Coelho/d  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
6) A Game of Thrones, George R. R. Martin, 864 

We can also specify an address range using textual pattern. The following example removes all pnes between the patterns Storm and Fellowship.

[jerry]$ sed  /Storm/,/Fellowship/d  books.txt  
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864 

In addition to this, we can also use dollar($), plus(+), and tilde(~) operators with SED.

Write Command

One of the important operations we perform on any file is backup, i.e., we make another copy of the file. SED provides the write command to store the contents of the pattern buffer in a file. Given below is the syntax of the write command which is similar to the delete command.

[address1[,address2]]w file 

Here, address1 and address2 are the starting and the ending address respectively, which can be either pne numbers or pattern strings. Both of these addresses are optional parameters.

In the above syntax, w refers to the write command and file is the file name in which you store contents. Be careful with the file parameter. When a file name is provided, the SED creates a file on the fly if it is not present, and overwrites it if it is already present.

Let us make an exact copy of the file using SED. Note that there must be exactly one space between w and file.

[jerry]$ sed -n  w books.bak  books.txt 

We created another file called books.bak. Now verify that both the files have identical content.

[jerry]$ diff books.txt books.bak  
[jerry]$ echo $?

On executing the above code, you get the following result:

0

You may assume that the cp command does exactly the same thing. Yes! The cp command does the same thing, but SED is a matured utipty. It allows creating a file containing only certain pnes from the source file. Let us store only even pnes to another file.

[jerry]$ sed -n  2~2 w junk.txt  books.txt  
[jerry]$ cat junk.txt 

On executing the above code, you get the following result:

2) The Two Towers, J. R. R. Tolkien, 352 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
6) A Game of Thrones, George R. R. Martin, 864 

You can also use comma(,), dollar($), and plus(+) operators with the write command.

In addition to this, SED also supports pattern matching with the write command. Suppose you want to store all the books of inspanidual authors into a separate file. One boring and lengthy way is do it manually, and the smarter way is to use SED.

[jerry]$ sed -n -e  /Martin/ w Martin.txt  -e  /Paulo/ w Paulo.txt  -e  /Tolkien/ w 
Tolkien.txt  books.txt 

In the above example, we are matching each pne against a pattern and storing the matched pne in a particular file. It is very simple. To specify multiple commands, we used -e switch of the SED command. Now let use see what each file contains:

[jerry]$ cat Martin.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
6) A Game of Thrones, George R. R. Martin, 864

Let us display the file contents.

[jerry]$ cat Paulo.txt

On executing the above code, you get the following result:

3) The Alchemist, Paulo Coelho, 197 
5) The Pilgrimage, Paulo Coelho, 288 

Let us display the file contents.

[jerry]$ cat Tolkien.txt

On executing the above code, you get the following result:

2) The Two Towers, J. R. R. Tolkien, 352 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 

Excellent! We got the expected result. SED is really an amazing utipty.

Append Command

One of the most useful operations of any text editor is to provide append functionapty. SED supports this operation through its append command. Given below is the syntax of append:

[address]a 
Append text 

Let us append a new book entry after pne number 4. The following example shows how to do it

[jerry]$ sed  4 a 7) Adultry, Paulo Coelho, 234  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
7) Adultry, Paulo Coelho, 234 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

In the command section, 4 imppes the pne number, a is the append command, and the remaining part is the text to be appended.

Let us insert a text pne at the end of the file. To do this, use $ as the address. The following example illustrates this:

[jerry]$ sed  $ a 7) Adultry, Paulo Coelho, 234  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864 
7) Adultry, Paulo Coelho, 234 

Apart from pne number, we can also specify an address using textual pattern. For instance, the following example appends text after matching the string The Alchemist.

[jerry]$ sed  /The Alchemist/ a 7) Adultry, Paulo Coelho, 234  books.txt  

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
7) Adultry, Paulo Coelho, 234 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864 

Note that if there are multiple patterns matching, then the text is appended after each match. The following example illustrates this scenario.

[jerry]$ sed  /The/ a 7) Adultry, Paulo Coelho, 234  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
7) Adultry, Paulo Coelho, 234 
3) The Alchemist, Paulo Coelho, 197 
7) Adultry, Paulo Coelho, 234 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
7) Adultry, Paulo Coelho, 234 
5) The Pilgrimage, Paulo Coelho, 288 
7) Adultry, Paulo Coelho, 234 
6) A Game of Thrones, George R. R. Martin, 864 

Change Command

SED provides change or replace command which is represented by c. This command helps replace an existing pne with new text. When pne range is provided, all the pnes are replaced as a group by a single text pne. Given below is the syntax of the change command:

[address1[,address2]]c 
Replace text

Let us replace the third pne with some other text.

[jerry]$ sed  3 c 3) Adultry, Paulo Coelho, 324  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) Adultry, Paulo Coelho, 324 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

SED also accepts patterns as an address. In the following example, a pne is replaced when the pattern match succeeds.

[jerry]$ sed  /The Alchemist/ c 3) Adultry, Paulo Coelho, 324  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) Adultry, Paulo Coelho, 324 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864 

SED also allows replacement of multiple pnes with a single pne. The following example removes pnes from fourth through sixth and replaces them with new text.

[jerry]$ sed  4, 6 c 4) Adultry, Paulo Coelho, 324  books.txt  

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
4) Adultry, Paulo Coelho, 324

Insert Command

The insert command works much in the same way as append does. The only difference is that it inserts a pne before a specific position. Given below is the syntax of the insert command:

[address]i 
Insert text 

Let us understand the insert command with some examples. The following command inserts a new entry before the fourth pne.

[jerry]$ sed  4 i 7) Adultry, Paulo Coelho, 324  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
7) Adultry, Paulo Coelho, 324 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

In the above example, 4 is the location number, i imppes the insert command, and the remaining part is the text to be inserted.

To insert text at the start of a file, provide the pne address as 1. The following command illustrates this:

[jerry]$ sed  1 i 7) Adultry, Paulo Coelho, 324  books.txt

On executing the above code, you get the following result:

7) Adultry, Paulo Coelho, 324 

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

Additionally, we can insert multiple pnes. The following command inserts two pnes before the last pne.

[jerry]$ sed  $ i 7) Adultry, Paulo Coelho, 324

On executing the above code, you get the following result:

8) Eleven Minutes, Paulo Coelho, 304  books.txt 
1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage,Paulo Coelho, 288 
7) Adultry, Paulo Coelho, 324 
8) Eleven Minutes, Paulo Coelho, 304 
6) A Game of Thrones, George R. R. Martin, 864

Note that the entries to be inserted are entered on separate pnes and depmited by the backslash() character.

Translate Command

SED provides a command to translate characters and it is represented as y. It transforms the characters by position. Given below is the syntax of the translate command:

[address1[,address2]]y/pst-1/pst-2/

Note that translation is based on the position of the character from pst 1 to the character in the same position in pst 2 and both psts must be exppcit character psts. Regular expressions and character classes are unsupported. Additionally, the size of pst 1 and pst 2 must be same.

The following example converts Arabic numbers to Roman numbers.

[jerry]$ echo "1 5 15 20" | sed  y/151520/IVXVXX/  

On executing the above code, you get the following result:

I V IV XX 

l command

Can you differentiate between words separated by spaces and words separated by tab characters only by looking at them? Certainly not. But SED can do this for you. SED uses the l command to display hidden characters in the text. For example, tab character with and End-Of-Line with $ character. Given below is the syntax of the l command.

[address1[,address2]]l 
[address1[,address2]]l [len] 

Let us create a file with tab characters for demonstration. For simppcity, we are going to use the same file, just by replacing spaces with tabs. Wait! But how to do that — by opening the file in a text editor and replacing each space with tab? Certainly not! We can make use of SED commands for that.

[jerry]$ sed  s/ /	/g  books.txt > junk.txt 

Now let us display the hidden characters by using the l command:

[jerry]$ sed -n  l  junk.txt

On executing the above code, you get the following result:

1)	A	Storm	of	Swords,George	R.	R.	Martin,1216$ 
2)	The	Two	Towers,J.	R.	R.	Tolkien,352$ 
3)	The	Alchemist,Paulo	Coelho,197$ 
4)	The	Fellowship	of	the	Ring,J.	R.	R.	Tolkien,432$ 
5)	The	Pilgrimage,Paulo	Coelho,288$ 
6)	A	Game	of	Thrones,George	R.	R.	Martin	,864$

Like other SED commands, it also accepts pne numbers and patterns as an address. You can try it yourselves.

Let us take a close look at another interesting feature of SED. We can instruct the SED to perform pne wrapping after a certain number of characters. The following example wraps pnes after 25 characters.

[jerry]$ sed -n  l 25  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords,Geo 
rge R. R. Martin,1216$ 
2) The Two Towers,J. R.  
R. Tolkien,352$ 
3) The Alchemist,Paulo C 
oelho,197$ 
4) The Fellowship of the 
 Ring,J. R. R. Tolkien,4 
32$ 
5) The Pilgrimage,Paulo  
Coelho,288$ 
6) A Game of Thrones,Geo 
rge R. R. Martin ,864$

Note that in the above example, wrap pmit is provided after l command. In this case, it is 25 characters. This option is GNU specific and may not work with other variants of the SED.

A wrap pmit of 0 means never break the pne unless there is a new pne character. The following simple command illustrates this.

[jerry]$ sed -n  l 0  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords,George R. R. Martin,1216$ 
2) The Two Towers,J. R. R. Tolkien,352$ 
3) The Alchemist,Paulo Coelho,197$ 
4) The Fellowship of the Ring,J. R. R. Tolkien,432$ 
5) The Pilgrimage,Paulo Coelho,288$ 
6) A Game of Thrones,George R. R. Martin,864$ 

Quit Command

Quit command instructs the SED to quit the current execution flow. It is represented by the q command. Given below is the syntax of the quit command:

[address]q 
[address]q [value]

Note that the quit command does not accept range of addresses, it only supports a single address. By default, SED follows read, execute, and repeat workflow; but when the quit command is encountered, it simply stops the current execution.

Let us print the first 3 pnes from the file.

[jerry]$ sed  3 q  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197

In addition to pne number, we can also use textual patterns. The following command quits when pattern match succeeds.

[jerry]$ sed  /The Alchemist/ q  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197

In addition to this, SED can also accept a value which can be used as the exit status. The following command shows its exit status as 100.

[jerry]$ sed  /The Alchemist/ q 100  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197

Now let us verify the exit status.

[jerry]$ echo $? 

On executing the above code, you get the following result:

100

Read Command

We can instruct the SED to read the contents of a file and display them when a specific condition matches. The command is represented by the alphabet r. Given below is the syntax of the read command.

[address]r file

Note that there must be exactly one space between the r command and the file name.

Let us understand it with a simple example. Create a sample file called junk.txt.

[jerry]$ echo "This is junk text." > junk.txt 

The following command instructs the SED to read the contents of junk.txt and insert them after the third pne.

[jerry]$ sed  3 r junk.txt  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
This is junk text. 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

In the above example, 3 imppes the pne address, r is the command name, and junk.txt is the file name the contents of which are to be displayed. Additionally, the GNU SED also accepts a range of addresses. For instance, the following command inserts the contents of junk.txt after the third, fourth, and fifth pnes.

[jerry]$ sed  3, 5 r junk.txt  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
This is junk text. 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
This is junk text. 
5) The Pilgrimage, Paulo Coelho, 288 
This is junk text. 
6) A Game of Thrones, George R. R. Martin, 864

Like other SED commands, the read command also accepts pattern as an address. For instance, the following command inserts the contents of junk.txt when the pattern match succeeds.

[jerry]$ sed  /Paulo/ r junk.txt  books.txt  

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
3) The Alchemist, Paulo Coelho, 197 
This is junk text. 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
This is junk text. 
6) A Game of Thrones, George R. R. Martin, 864 

Execute Command

We can execute external commands from SED using the execute command. It is represented by e. Given below is the syntax of the execute command.

[address1[,address2]]e [command]

Let us illustrate the execute command with a simple example. The following SED command executes the UNIX date command before the third pne.

[jerry]$ sed  3 e date  books.txt

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
Sun Sep  7 18:04:49 IST 2014 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

Like other commands, it also accepts patterns as an address. For example, the following example executes date command when a pattern match succeeds. Note that after each pattern match, first the command is executed and then the contents of the pattern buffer are displayed.

[jerry]$ sed  /Paulo/ e date  books.txt 

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216 
2) The Two Towers, J. R. R. Tolkien, 352 
Sun Sep  7 18:06:04 IST 2014 
3) The Alchemist, Paulo Coelho, 197 
4) The Fellowship of the Ring, J. R. R. Tolkien, 432 
Sun Sep  7 18:06:04 IST 2014 
5) The Pilgrimage, Paulo Coelho, 288 
6) A Game of Thrones, George R. R. Martin, 864

If you observe the syntax of the e command carefully, you will notice that command is optional. When no command is provided after e, it treats the contents of the pattern buffer as an external command. To illustrate this, let us create a commands.txt file with a few simple commands.

[jerry]$ echo -e "date
cal
uname" > commands.txt 
[jerry]$ cat commands.txt

On executing the above code, you get the following result:

date 
cal 
uname

Commands from the file are self-explanatory. In the absence of command after e, SED executes all these commands one by one. The following simple example illustrates this.

[jerry]$ sed  e  commands.txt 

On executing the above code, you get the following result:

Sun Sep  7 18:14:20 IST 2014 
   September 2014      
Su Mo Tu We Th Fr Sa   
    1  2  3  4  5  6   
 7  8  9 10 11 12 13   
14 15 16 17 18 19 20   
21 22 23 24 25 26 27   
28 29 30               
                       
Linux 

Like other SED commands, the execute command also accepts all vapd ranges of addresses.

Miscellaneous Commands

By default, SED operates on single pne, however it can operate on multiple pnes as well. Multi-pne commands are denoted by uppercase letters. For example, unpke the n command, the N command does not clear and print the pattern space. Instead, it adds a newpne ( ) at the end of the current pattern space and appends the next pne from the input-file to the current pattern space and continues with the SED s standard flow by executing the rest of the SED commands. Given below is the syntax of the N command.

[address1[,address2]]N

Let us print a comma-separated pst of book titles and their respective authors. The following example illustrates this.

[jerry]$ sed  N; s/
/, /g  books.txt 

On executing the above code, you get the following result:

A Storm of Swords, George R. R. Martin 
The Two Towers, J. R. R. Tolkien 
The Alchemist, Paulo Coelho 
The Fellowship of the Ring, J. R. R. Tolkien 
The Pilgrimage, Paulo Coelho 
A Game of Thrones, George R. R. Martin

Let us understand how the above example works. The N command reads the first pne, i.e.,A Storm of Swords into the pattern buffer and appends followed by the next pne. The pattern space now contains A Storm of Swords George R. R. Martin. In the next step, we are replacing the newpne with a comma.

Like p command, we have a P command to print the first part (up to embedded newpne) of the multi-pne pattern space created by the N command. Given below is the syntax of the P command which is similar to the p command.

[address1[,address2]]P 

In the previous example, we saw that the N command creates a newpne- separated pst of book titles and their authors. Let us print only the first part of it, i.e., only the titles of the book. The following command illustrates this.

[jerry]$ sed -n  N;P  books.txt

On executing the above code, you get the following result:

A Storm of Swords 
The Two Towers 
The Alchemist 
The Fellowship of the Ring 
The Pilgrimage 
A Game of Thrones

Note that in the absence of N, it behaves same as the p command. The following simple command illustrates this scenario.

[jerry]$ sed -n  P  books.txt

On executing the above code, you get the following result:

A Storm of Swords 
George R. R. Martin 
The Two Towers 
J. R. R. Tolkien 
The Alchemist 
Paulo Coelho 
The Fellowship of the Ring 
J. R. R. Tolkien 
The Pilgrimage 
Paulo Coelho 
A Game of Thrones 
George R. R. Martin

In addition to this, SED also provides a v command which checks for version. If the provided version is greater than the installed SED version, then the command execution fails. Note that this option is GNU specific and may not work with other variants of SED. Given below is the syntax of the v command.

[address1[,address2]]v [version]

First, find out the current version of SED.

[jerry]$ sed --version 

On executing the above code, you get the following result:

sed (GNU sed) 4.2.2 

In the following example, the SED version is greater than version 4.2.2, hence the SED command aborts its execution.

[jerry]$ sed  v 4.2.3  books.txt 

On executing the above code, you get the following result:

sed: -e expression #1, char 7: expected newer version of sed

But if the provided version is lesser than or equal to version 4.2.2, then the command works as expected.

[jerry]$ sed  v 4.2.2  books.txt

On executing the above code, you get the following result:

A Storm of Swords 
George R. R. Martin 
The Two Towers 
J. R. R. Tolkien 
The Alchemist 
Paulo Coelho 
The Fellowship of the Ring 
J. R. R. Tolkien 
The Pilgrimage 
Paulo Coelho 
A Game of Thrones George R. R. Martin