Difference between revisions of "BOSS-Linux/C3/The-sed-command/English-timed"

|  Welcome to this spoken tutorial on '''sed''' - the stream editor.

|  In this tutorial  we will learn usage of '''sed '''command.

|We will do through some examples

| As prerequisites

|You should know Basics of linux terminal

|For relevant tutorials please visit our website which as shown: http://spoken-tutorial.org  

| Let us with an introduction to '''sed'''

|'''sed''' is a stream editor.  

|It performs some display or editing function

|editing function like insertion, substitution and deletion in matched text.

| Let us first start with some examples.

|I have a file called '''seddemo.txt''' in home directory version.  

|Let us view its content.

|In this file we have some enteries like roll no, name, stream, marks, pass or fail and the stipend amount.

|Now suppose we want to print the second line of the file.

|For this we need to open the terminal  

|Now Type

 

| 01:48

|'''sed''' space within  single quotes ‘'''2p’''' after the single quotes space '''seddemo.txt'''

|Press '''Enter'''

|Here '''2''' denotes the location which is the second line.

|'''p''' denotes the action, which is printing('''p''').

|Now Look at the output.

|This is the default behaviour of the action '''p'''.

|To only print the second line

|Type '''sed '''space  '''-n''' space (Within single quotes) '''2p''' after the single quotes space '''seddemo.txt '''

|We see only the second line as printed.

|Then we give the location in the stream that we want to edit or display.  

|'''p''' indicates the action we want to take ie to print the second line.

|And '''seddemo.txt''' is the name of the file

|This is the general syntax of sed command.

|Now let us print the last line of the file.

|Let me clear the promt

|Now Type

 

| 03:25

|'''sed''' space  '''-n''' space within single quotes (dollar) '''$p''' after the single quotes space '''seddemo.txt '''

|Now come back to text editor.

| Suppose we want to print the enteries from 3rd to 6th

|For this we need to type on the terminal:  

|'''sed''' space  '''-n''' space within single quotes '''3''' (comma) ''',6p’''' space '''seddemo.txt '''

|'''Press Enter.'''

| Any of the actions can be reversed by using the exclamation mark before the action.

|Say if we had to print all lines except from 3rd to 6th we will type:

'''sed''' space  '''-n''' space within single quotes ‘'''3''' (comma) ''',6''' (exclamation mark) '''!p'''  

|'''Press''' '''Enter.'''

 

|The output is displayed.

|This is known as line addressing.

|Address specified by the line numbers.

|Another way of addressing is '''Context addressing'''

|If we want to take actions on lines that contain a particular word we use context addressing.

|Regular expressions can be used.  

|Come back to our editor.

|  Say we want to print those lines which have the word '''computers'''.

|Now Type

|'''sed''' space '''-n''' space (within single quotes) (front slash)(opening square bracket) '''[cC]''' (Closing Square bracket)  '''omputers/p''' after the single quotes'''space '''seddemo.txt '''

|'''Press''' '''Enter.'''

|We see the lines with the word computers is displayed.

|We write pattern within square brackets.  

|This is to match any one or both of the characters within square brackets.

|When we need to match patterns the pattern needs to be typed between front slashes.

| We can print it in file as well using the '''w''' option.  

 

|For this type:

|'''sed''' space '''-n''' space (within single quotes) (front slash) (opening square bracket)  '''[cC] (closing square bracket)omputers/w''' space '''computer_student.txt''' after the single quotes space '''seddemo.txt '''

|'''Press''' '''Enter.'''

|Now all the matching lines would be transferred to the file '''computer_student.txt'''.  

| Let us view the content

| Type '''cat''' space '''computer_student'''.txt

|'''Press Enter.'''

|We see the entries

| Let us clear the promt

| Type '''sed''' space '''-n''' space '''-e''' space (within single quotes) (front slash) '''‘/electronics/w''' space '''electro.txt’''' after the single quotes space  '''-e''' space (within single quotes) (front slash) '''‘/civil/w''' space '''civil.txt’''' after the single quote  space '''seddemo.txt '''

|Press '''Enter'''

|Here '''-e''' is used to combine multiple methods''' '''

|This would create two files '''electro.txt''' and '''civil.txt'''.  

| To see what they contain type:

|This will display the enteries with the word electronics.

|Let us see the content of civil file.

| Type '''cat '''space''' civil.txt'''

|''' press Enter'''

|This will display the enteries having the word civil.

|Let us switch back to our slide

| we will  summarize,

 

|In this tutorial we learnt,sed

|To print using '''sed.'''

 

|Line Addressing.  

| As an assignment,

|Use the same text file '''seddemo.txt.'''

| Watch the video available at the link shown below

|It summarises the Spoken Tutorial project

|If you do not have good bandwidth, you can download and watch it

|  The Spoken Tutorial Project Team

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