sed - dwilson2547/wiki_demo GitHub Wiki

Here’s a comprehensive sed cheat sheet with common commands and practical examples:

sed (stream editor) is a powerful Linux command for parsing and transforming text.

• sed Cheat Sheet
• 1. Basic Syntax
• 2. Common Commands
  • 2.1. Substitution (s)
  • 2.2. Global Substitution (g)
  • 2.3. Case-Insensitive Substitution (i)
  • 2.4. Delete Lines (d)
  • 2.5. Print Lines (p)
  • 2.6. Line Numbers
  • 2.7. Insert (i) and Append (a)
  • 2.8. Change Line (c)
  • 2.9. In-Place Editing (-i)
  • 2.10. Multiple Commands (-e)
  • 2.11. Address Ranges
  • 2.12. Regular Expressions
  • 2.13. Read from a File (r)
  • 2.14. Write to a File (w)
  • 2.15. Quit (q)
• 3. Advanced Examples
  • 3.1. Remove Empty Lines
  • 3.2. Remove Comments
  • 3.3. Double Space a File
  • 3.4. Number Lines
  • 3.5. Extract Email Addresses
• 4. Common Use Cases
• 5. Tips and Tricks

sed [options] 'command' [input-file]

• Options:
  • -n: Suppress automatic printing of pattern space.
  • -i: Edit files in-place (use with caution!).
  • -e: Specify multiple commands.
  • -f: Read commands from a file.

Replace text patterns.

sed 's/old-text/new-text/' file.txt

• Replace the first occurrence of old-text with new-text in each line.

Example:

sed 's/foo/bar/' file.txt

• Replaces foo with bar in file.txt.

Replace all occurrences of a pattern in a line.

sed 's/old-text/new-text/g' file.txt

Example:

sed 's/apple/orange/g' file.txt

• Replaces all instances of apple with orange.

sed 's/old-text/new-text/gi' file.txt

Example:

sed 's/cat/dog/gi' file.txt

• Replaces cat, Cat, CAT, etc., with dog.

Delete lines matching a pattern.

sed '/pattern/d' file.txt

Example:

sed '/error/d' logfile.txt

• Deletes all lines containing error.

Print lines matching a pattern.

sed -n '/pattern/p' file.txt

Example:

sed -n '/success/p' logfile.txt

• Prints only lines containing success.

Print or delete lines by number.

sed -n '5p' file.txt          # Print line 5
sed '3d' file.txt             # Delete line 3
sed -n '1,10p' file.txt       # Print lines 1 to 10

Example:

sed -n '10,20p' data.txt

• Prints lines 10 to 20.

Insert or append text before/after a line.

sed '3i\new line' file.txt    # Insert before line 3
sed '5a\new line' file.txt    # Append after line 5

Example:

sed '1i\# Header' file.txt

• Inserts # Header at the beginning of the file.

Replace an entire line.

sed '3c\new line' file.txt

Example:

sed '2c\This is the new second line' file.txt

• Replaces the second line with This is the new second line.

Edit files directly (use with caution!).

sed -i 's/old/new/' file.txt

Example:

sed -i 's/windows/linux/g' config.txt

• Replaces windows with linux in config.txt and saves changes.

Execute multiple commands.

sed -e 's/foo/bar/' -e 's/baz/qux/' file.txt

Example:

sed -e 's/red/blue/' -e 's/small/large/' colors.txt

• Replaces red with blue and small with large.

Apply commands to a range of lines.

sed '3,6s/old/new/' file.txt

Example:

sed '10,20s/yes/no/' survey.txt

• Replaces yes with no in lines 10 to 20.

Use regex for complex pattern matching.

sed -n '/^[A-Z]/p' file.txt       # Print lines starting with a capital letter
sed 's/[0-9]\{3\}/NUM/g' file.txt # Replace 3-digit numbers with "NUM"

Example:

sed -n '/^[A-Za-z]/p' names.txt

• Prints lines starting with a letter.

Insert the contents of a file.

sed '3r newfile.txt' file.txt

Example:

sed '1r header.txt' data.txt

• Inserts the contents of header.txt after line 1 of data.txt.

Write matching lines to a file.

sed -n '/error/w errors.txt' logfile.txt

Example:

sed -n '/404/w 404_errors.txt' access.log

• Writes all lines containing 404 to 404_errors.txt.

Exit after processing a specific line.

sed '10q' file.txt

Example:

sed '50q' largefile.txt

• Prints the first 50 lines and exits.

sed '/^$/d' file.txt

sed 's/#.*//' config.txt

sed G file.txt

sed = file.txt | sed 'N;s/\n/\t/'

sed -n 's/.*\([a-zA-Z0-9._-]@[a-zA-Z0-9._-]\{2,\}.[a-zA-Z]\{2,\}\).*/\1/p' file.txt

• Backup Files: Always back up files before using -i:

  sed -i.bak 's/old/new/g' file.txt

• Test First: Use sed without -i to preview changes.
• Combine Commands: Use -e for multiple operations.
• Debugging: Use echo and pipes to test patterns:

  echo "test" | sed 's/test/hello/'