How to use the command 'realpath' (with examples)

The realpath command is a helpful utility found in many Unix-like operating systems. It is used to resolve the absolute path of files and directories. This command is particularly useful in scripts and in environments where a canonical path is necessary. It can handle symbolic links and can be used to require paths to exist before working with them. Here we’ll explore various use cases of the realpath command with detailed examples.

Use case 1: Display the absolute path for a file or directory

Code:

realpath path/to/file_or_directory

Motivation:

The need to convert a relative path to an absolute path is common in scripting and command-line operations. Using absolute paths eliminates ambiguity, ensuring that scripts and commands interact with the intended files, regardless of the current working directory. This use case is particularly beneficial when deploying scripts across different environments where the paths may vary.

Explanation:

• realpath: Invokes the command, which resolves the specified path to its absolute form.
• path/to/file_or_directory: This is the relative path that you want to convert to an absolute path. It could be a single file or a directory.

Example output:

/home/user/documents/project/file.txt

This output indicates the absolute path of the specified file within the filesystem.

Use case 2: Require all path components to exist

Code:

realpath --canonicalize-existing path/to/file_or_directory

Motivation:

When working with critical operations, it’s important to ensure that every component in a path actually exists. By using this option, you can enforce the requirement that all directories and files in the path must exist, which helps prevent errors in subsequent processes that assume the presence of these components.

Explanation:

• --canonicalize-existing: This option ensures that all components in the specified path exist. If any part of the path does not exist, realpath will return an error.

Example output:

/home/user/documents/project/file.txt

This reflects the confirmed existence of the entire path, showing that each directory and file named in the path are present.

Use case 3: Resolve “..” components before symlinks

Code:

realpath --logical path/to/file_or_directory

Motivation:

In cases where the path includes parent directory references (..), resolving these before expanding symbolic links can reveal the intended file structure, especially when symlinks could mislead the actual component order. It’s useful in environments where paths might loop or be expected to map in a certain logical structure.

Explanation:

• --logical: This option ensures that .. components in a path are resolved before any symlinks, providing a logical view of the path structure as opposed to following physical symlinks first.

Example output:

/home/user/project/file.txt

This output provides the logical path, as seen by resolving .. components first, disregarding symlink alterations.

Use case 4: Disable symlink expansion

Code:

realpath --no-symlinks path/to/file_or_directory

Motivation:

Sometimes it’s necessary to obtain the path without interpreting symbolic links, especially if you are working on systems where the symbolic links could lead to different locations, or when you want to record the path as seen without changes from symlinks. This can be crucial for documentation or analysis purposes.

Explanation:

• --no-symlinks: Disables the normal behavior of expanding symbolic links, returning the path with symlink components unaffected.

Example output:

/home/user/shortcuts/file.txt

This output shows the literal path including any symlinks as they are, without following them to their actual destinations.

Use case 5: Suppress error messages

Code:

realpath --quiet path/to/file_or_directory

Motivation:

In scripting and automation scenarios, you might want to handle paths where components may not currently exist and suppress error messages to maintain log clarity or to handle errors in a custom manner. Using --quiet helps in managing logs and outputs effectively.

Explanation:

• --quiet: This suppresses the error messages that realpath might generate, allowing scripts to proceed or handle errors independently.

Example output:

When the specified path does not exist, instead of producing an error output, the command will just return nothing or handle it silently according to the script’s design.

Conclusion:

The realpath command is a versatile utility for managing and resolving path specifications in Unix-like environments. From ensuring paths exist to managing symlinks and handling parent directories, it is an indispensable tool in the command-line toolkit, providing clear and consistent path management options for various use cases.