What are advanced sed features?

Here are some advanced features of sed that enhance its text processing capabilities:

1. Addressing

You can specify line ranges or patterns to apply commands only to specific lines:

sed '1,5s/old/new/g' filename.txt  # Replace in lines 1 to 5
sed '/pattern/s/old/new/g' filename.txt  # Replace in lines matching 'pattern'

2. Hold Space

sed has a hold space that allows you to temporarily store text for later use:

sed -e '1h' -e '2G' filename.txt  # Copy line 1 to hold space, then append it to line 2

3. Multiple Commands

You can execute multiple commands in a single sed invocation using -e or by separating commands with a semicolon:

sed -e 's/old/new/g' -e '2d' filename.txt

or

sed 's/old/new/g; 2d' filename.txt

4. Using Regular Expressions

sed supports extended regular expressions with the -E option, allowing for more complex pattern matching:

sed -E 's/(old|new)/replacement/g' filename.txt  # Replace 'old' or 'new'

5. Conditional Execution

You can use the t command to branch based on whether a substitution was made:

sed '/pattern/{s/old/new/g; t; s/another/replace/g;}' filename.txt

6. Appending and Prepending

You can append or prepend text to lines:

sed '2a\This is appended text' filename.txt  # Append after line 2
sed '2i\This is prepended text' filename.txt  # Prepend before line 2

7. Using Shell Variables

You can use shell variables within sed commands:

var="replacement"
sed "s/old/$var/g" filename.txt

8. Reading from a File

You can read commands from a separate file using the -f option:

sed -f commands.sed filename.txt

These advanced features make sed a powerful tool for complex text processing tasks in scripts and command-line operations.