Lập trình shell

• sed (viết tắt của stream editor) là một chương trình soạn thảo text từ stdin, theo phương thức từng dòng và không có tương tác
• sed không thay thế được cho các hệ soạn thảo text có tương tác, nhưng là một công cụ mạnh để xử lý text khi viết shell script

• Cách sử dụng sed phổ biến nhất là từ dòng lệnh:

sed [options] commands [file-to-edit]

• Có thể sử dụng sed kết hợp với các cơ chế định hướng lại vào/ra, pipe của UNIX:

command | [sed options] commands

hoặc

sed [options] commands < file

• Lệnh của sed thường được nằm trong cặp dấu ''

• Cách sử dụng đơn giản nhất, với lệnh rỗng:

sed '' test.txt

## 1 Introduction
## 2
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• Hoặc sed '' < test.txt hoặc cat test.txt | sed ''

sed '1p' test.txt

## 1 Introduction
## 1 Introduction
## 2
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

sed -n '3p' test.txt

## 3 The sed stream editor is a text editor that performs editing operations on information

sed -n '1,3p' test.txt

## 1 Introduction
## 2
## 3 The sed stream editor is a text editor that performs editing operations on information

sed -n '2,+2p' test.txt

## 2
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 

• Lưu ý: Dòng đầu tiên của file là 1, dòng cuối cùng của file là $

sed -n '1~2p' test.txt

## 1 Introduction
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 5
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,

sed -n '1,2!p' test.txt

## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

sed -n '1~2!p' test.txt

## 2
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 8 but it is a very powerful and fast way to transform text.

sed '3i New line before 3rd line' test.txt

## 1 Introduction
## 2
## New line before 3rd line
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

sed '1~2d' test.txt

## 2
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 8 but it is a very powerful and fast way to transform text.

sed '1,2d' test.txt

## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

sed -n '/edit/p' test.txt

## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 6 This means that you make all of the editing decisions as you are calling the command and       

• Thay thế text là một trong các ứng dụng phổ biến nhất của sed: 's/old word/new word/': Thay thế lần xuất hiện đầu tiên của old word bằng new word

cat test.txt | sed 's/line/LINE/'

## 1 Introduction
## 2
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits LINE-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• 's/old word/new word/g': Thay thế toàn bộ các từ old word bằng new word

cat test.txt | sed 's/line/LINE/g'

## 1 Introduction
## 2
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits LINE-by-LINE and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• 's/old word/new word/n': Thay thế lần xuất hiện thứ n của old word bằng new word, trong đó n là một số nguyên dương

cat test.txt | sed 's/edit/EDIT/2'

## 1 Introduction
## 2
## 3 The sed stream editor is a text EDITor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• Có thể dùng tham số p trong phần cuối của lệnh tìm kiếm để in ra các dòng có thay đổi:

cat test.txt | sed -n 's/edit/EDIT/2p'

## 3 The sed stream editor is a text EDITor that performs editing operations on information

• Tìm text bắt đầu từ đầu dòng đến "ing":

sed 's/^.*ing/REPLACED/' test.txt

## 1 Introduction
## 2
## REPLACED operations on information  
## REPLACED from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## REPLACED the command and     
## REPLACED or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• Thêm cặp dấu ngoặc vào mẫu text được tìm thấy:

sed 's/^.*ing/(&)/' test.txt

## 1 Introduction
## 2
## (3 The sed stream editor is a text editor that performs editing) operations on information  
## (4 coming) from standard input or a file. Sed edits line-by-line and in a non-interactive way.   
## 5
## (6 This means that you make all of the editing decisions as you are calling) the command and     
## (7 sed will execute the directions automatically. This may seem confusing) or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• Cách 1: sed 'command 1' file | sed 'command 2'
  • Tốn bộ nhớ và phải tạo nhiều tiến trình
  • Thích hợp cho các lệnh cần có sự tuần tự về dữ liệu output
• Cách 2: sed -e 'command 1' -e 'command 2' file
• Cách 3: sed 'command 1;command2' file

sed -n '3p' test.txt | sed 's/ing/ING/'
sed -n -e '3p' -e's/ing/ING/' test.txt
sed -n '3p;s/ing/ING/' test.txt

## 3 The sed stream editor is a text editor that performs editING operations on information  
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 3 The sed stream editor is a text editor that performs editing operations on information

• sed cho phép sử dụng biểu thức chính qui trong tìm kiếm. Ví dụ sau thay 2 dòng đầu tiên bằng REPLACED:

sed '1,2s/.*/REPLACED/' test.txt

## REPLACED
## REPLACED
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 8 but it is a very powerful and fast way to transform text.

• Ví dụ sau thay it bằng IT cho tất cả các dòng chứa ing:

sed '/ing/s/it/IT/g' test.txt

## 1 Introduction
## 2
## 3 The sed stream edITor is a text edITor that performs edITing operations on information  
## 4 coming from standard input or a file. Sed edITs line-by-line and in a non-interactive way. 
## 5
## 6 This means that you make all of the edITing decisions as you are calling the command and       
## 7 sed will execute the directions automatically. This may seem confusing or unintuITive,
## 8 but it is a very powerful and fast way to transform text.

• Buffer = vùng nhớ tạm thời có thể được thay đổi bởi các lệnh sed kế tiếp.
• Các lệnh với buffer:
  • h: copy mẫu tìm kiếm hiện tại vào buffer (và do đó xóa nội dung trước của buffer)
  • H: copy mẫu tìm kiếm hiện tại nối tiếp vào buffer (append), phân cách nhau bởi dấu xuống dòng \n
  • g: copy nội dung buffer vào mẫu tìm kiếm hiện tại
  • G: nối nội dung buffer vào mẫu tìm kiếm hiện tại, phân cách nhau bởi dấu \n
  • x: Đổi nội dung mẫu tìm kiếm hiện tại và buffer cho nhau

sed -n '1~2h;g;s/it/IT/p' test.txt

## 3 The sed stream edITor is a text editor that performs editing operations on information  
## 3 The sed stream edITor is a text editor that performs editing operations on information  
## 7 sed will execute the directions automatically. This may seem confusing or unintuITive,
## 7 sed will execute the directions automatically. This may seem confusing or unintuITive,

sed -n '2,$G;h;$p' test.txt

## 8 but it is a very powerful and fast way to transform text.
## 7 sed will execute the directions automatically. This may seem confusing or unintuitive,
## 6 This means that you make all of the editing decisions as you are calling the command and       
## 5
## 4 coming from standard input or a file. Sed edits line-by-line and in a non-interactive way. 
## 3 The sed stream editor is a text editor that performs editing operations on information  
## 2
## 1 Introduction

• Viết các lệnh sed trong một file, sau đó sử dụng lệnh sed -f sed_script_file

cat sedscript

## s/it/IT/g
## 1,3p

sed -n -f sedscript test.txt

## 1 Introduction
## 2
## 3 The sed stream edITor is a text edITor that performs edITing operations on information

• 5.1. Xóa 3 dòng đầu tiên của 1 file và đưa các dòng còn lại ra màn hình
• 5.2. Hãy xóa các dòng trắng của một file và đưa các dòng còn lại ra màn hình
• 5.3. Hãy tìm các dòng của file có ký tự trắng ở cuối dòng và in ra các dòng đó
• 5.4. Hãy thay thế từ Multics (không phân biệt chữ hoa/thường) bằng MULTICS trong file sedtext.txt
• 5.5. Hãy đếm tần suất các từ xuất hiện trong một file text và in ra các từ kèm theo tần suất tương ứng (Lưu ý không phân biệt chữ hoa/thường)