Using the 'ed' Command (with Examples)

The ed command is a line-oriented text editor that was one of the first in Unix systems. It operates interactively, allowing the editing of text files through a command-line interface. Despite being overshadowed by more modern editors like vi and nano, ed remains an efficient tool for quick and specific text manipulations, particularly for use cases where automation or scripting is beneficial.

Use Case 1: Start an Interactive Editor Session with an Empty Document

Code:

ed

Motivation:

Starting ed with an empty document is a fundamental operation to know when you need to create a new document from scratch. This can be useful in environments where you need to start jotting down text or code snippets directly into a new file without opening a graphical text editor, especially in systems with limited resources or interfaces.

Explanation:

• When you simply type ed in the shell and press enter, an interactive session is initiated where no text document is preloaded. This means that you start with a blank canvas, allowing you to input and edit text immediately.

Example Output:

?

Here, the question mark (?) signifies that ed is waiting for your input or commands since the document is empty.

Use Case 2: Start an Interactive Editor Session with an Empty Document and a Specific [p]rompt

Code:

ed -p '> '

Motivation:

Using a custom prompt can be particularly helpful when working in a multi-user environment or when issuing commands to ed in automation scripts where distinguishing the editor input part from the rest of the terminal prompt makes the workflow clearer.

Explanation:

• -p '> ': The -p option allows you to set a custom prompt string. Here, '> ' is defined as the prompt for the session, making it easier to identify where ed’s input begins and ends.

Example Output:

> 

This indicates that ed is running with a custom prompt, which visually marks the editing interface.

Use Case 3: Start an Interactive Editor Session with an Empty Document and Without Diagnostics, Byte Counts, and ‘!’ Prompt

Code:

ed -s

Motivation:

Suppressing diagnostics and other feedback can be beneficial in scripting or logging scenarios where extraneous information might clutter outputs. This aids in creating cleaner logs or scripts where only specific results or changes are desired.

Explanation:

• -s: The -s flag stands for ‘silent’ mode. It suppresses any error messages, byte counts, and the ! prompt, making your editing session cleaner and quieter.

Example Output:

(No output as diagnostics and prompts are suppressed)

Use Case 4: Edit a Specific File (Shows the Byte Count of the Loaded File)

Code:

ed path/to/file

Motivation:

Editing an existing file directly through a simple command allows for quick modifications without the overhead of opening a graphical editor. Knowing the byte count immediately is useful for confirming that the whole document has been loaded correctly, especially for larger files or troubleshooting data integrity issues.

Explanation:

• path/to/file: This part specifies the path to the file you wish to edit. Upon loading, ed will display the number of bytes read, thereby confirming the file’s size in bytes, which is an immediate verification step for file integrity.

Example Output:

123

This indicates that 123 bytes have been loaded from the specified file into the ed session.

Use Case 5: Replace a String with a Specific Replacement for All Lines

Code:

,s/regular_expression/replacement/g

Motivation:

Performing search and replace operations throughout an entire document is a powerful feature of ed. When handling files that require bulk editing, such as configuration files or large datasets, this command allows batch processing of text changes with precision and efficiency.

Explanation:

• ,: The leading comma specifies that the operation applies to all lines.
• s/regular_expression/replacement/g: The s command is used for substitution. regular_expression represents the text pattern to search for, and replacement is the text to replace it with. The g flag stands for global, meaning the replacement occurs for every match on each line.

Example Output:

(No direct output; The document contents are modified by the substitution command)

Conclusion:

The ed command, despite being somewhat arcane, offers powerful functionalities for text editing directly within a command-line interface. Whether you’re creating new documents, editing existing ones, or performing complex text manipulations, mastering these common use cases enhances productivity, especially in environments reliant on scripts or automation.