sed

#sed

# 文件中第6行插入一行
sed -i '6i this is the new line' test.txt
sed -i 's/原始内容/替换内容/\$' 文件名
#替换文件中第6行
sed -i '6s/.*/替换内容/'
sed -n '\$p' 文件名
# 删除文件中的第4行到文件尾
sed -i '4,\$d' 文件名
# 删除空行
sed  '/^&/d' 文件名

sed (stream editor) is a powerful command-line utility used for parsing and transforming text in a stream or file. Here is a summary of common sed usage and commands:

Basic Usage

sed [options] 'script' [file...]

• script: The set of instructions to be applied to the input text.
• file...: One or more files to be processed. If no file is specified, sed reads from standard input.

Common Options

• -n: Suppresses automatic printing of pattern space. Use with the p command to print specific lines.
• -e script: Adds the script to the commands to be executed.
• -f script-file: Adds the contents of script-file to the commands to be executed.
• -i[SUFFIX]: Edits files in place (makes backup if extension is supplied).

Addressing

sed commands can be restricted to specific lines or ranges of lines:

• number: A specific line number.
• $: The last line.
• /regex/: Lines matching the regular expression regex.
• addr1,addr2: A range of lines from addr1 to addr2.

Commands

• p: Print the current pattern space.
• d: Delete the pattern space (do not print it).
• s/regexp/replacement/flags: Substitute regexp with replacement. Common flags include:
  • g: Global replacement (all occurrences).
  • i: Case-insensitive replacement.
  • p: Print the result of the substitution.
  • w file: Write the result to file.
• a\ text: Append text after each line matched.
• i\ text: Insert text before each line matched.
• c\ text: Replace lines with text.
• y/src/dest/: Transliterate characters (like tr command).

Examples

1. Print specific lines:

   sed -n '5p' file.txt  # Print the 5th line
   sed -n '5,10p' file.txt  # Print lines 5 to 10
   

2. Substitute text:

   sed 's/foo/bar/' file.txt  # Replace first occurrence of 'foo' with 'bar' in each line
   sed 's/foo/bar/g' file.txt  # Replace all occurrences of 'foo' with 'bar' in each line
   

3. Delete lines:

   sed '3d' file.txt  # Delete the 3rd line
   sed '/^$/d' file.txt  # Delete all empty lines
   

4. Insert and append text:

   sed '3i\Inserted text' file.txt  # Insert text before the 3rd line
   sed '3a\Appended text' file.txt  # Append text after the 3rd line
   

5. Extract a block of text:

   sed -n '/start/,/end/p' file.txt  # Print lines from 'start' to 'end'
   

6. In-place editing:

   sed -i 's/foo/bar/g' file.txt  # Replace 'foo' with 'bar' directly in the file
   sed -i.bak 's/foo/bar/g' file.txt  # Same as above but create a backup with .bak extension
   

7. Using multiple commands:

   sed -e 's/foo/bar/' -e '/baz/d' file.txt  # Substitute and delete in one command
   

Special Characters

• &: Represents the matched text in the replacement part of the s command.

  sed 's/foo/&bar/' file.txt  # Replaces 'foo' with 'foobar'
  

• \1, \2, ... \9: Refer to matched groups in the pattern.

  sed 's/\(foo\) \(bar\)/\2 \1/' file.txt  # Swaps 'foo bar' to 'bar foo'
  

Escaping Characters

Characters like /, &, and \ have special meanings in sed and must be escaped with a backslash (\) if they are to be used literally.

By mastering these sed commands and techniques, you can efficiently manipulate and transform text in a variety of powerful ways directly from the command line.