sed (stream editor) is a powerful text processing tool in Unix and Unix-like operating systems. It is used to perform basic text transformations on an input stream (a file or input from a pipeline). sed is commonly used for:

• Searching and replacing text
• Inserting and deleting lines
• Performing complex text manipulations

The basic syntax of sed is:

• options: Command-line options to modify the behavior of sed.
• script: A set of instructions to be executed on the input text.
• inputfile: The file to be processed. If omitted, sed reads from standard input.

• -e script: Add the script to the commands to be executed.
• -f script-file: Add the contents of the script-file to the commands to be executed.
• -i[SUFFIX]: Edit files in place (makes backup if SUFFIX supplied).
• -n: Suppress automatic printing of pattern space.

The substitution command (s) is used to replace occurrences of a pattern with a replacement string.

Example:

Output:

The delete command (d) is used to delete lines matching a pattern.

Example:

Output:

• i\text: Insert text before a line.
• a\text: Append text after a line.

Example:

Output:

Replace all occurrences of "foo" with "bar" in a file:

Remove all blank lines from a file:

Insert "New Line" after every line containing "pattern":

Combine sed with other commands using pipelines:

Replace "apple" with "orange" in the following text:

Solution:

Output:

Delete lines containing the word "delete" from the following text:

Solution:

Output:

Insert "Start of File" at the beginning of the file:

Solution:

Output:

• Forgetting the g flag: When replacing all occurrences of a pattern in a line, don't forget to use the g flag.
• Using single quotes: Always use single quotes around the sed script to avoid shell interpretation of special characters.
• Backup files: When using -i for in-place editing, consider making a backup by providing a suffix (e.g., -i.bak).

In this section, we covered the basics of using sed for text processing, including substitution, deletion, and insertion of text. We also explored practical examples and exercises to reinforce the concepts. Understanding sed is crucial for efficient text manipulation in Bash scripting, and it serves as a foundation for more advanced text processing tasks.