exch

Swap filepaths

$ exch [path/to/file1] [path/to/file2]

exch file1 file2

file1
    The first file whose content will be exchanged.

file2
    The second file whose content will be exchanged.

The `exch` command is a simple utility that exchanges the contents of two specified files. It achieves this by renaming the files such that their contents are effectively swapped. It provides a straightforward mechanism for manipulating file content at the filesystem level. It is typically used in scripting or automated processes where rapid content swapping is required. Because exch manipulates actual files there is no need to copy, edit or overwrite files to perform an interchange. It is important to be aware that any existing hard links to either file will point to the swapped content after the command is executed. Backups of the original files before using `exch` are recommended, especially in production environments, to mitigate the risk of data loss due to unexpected behavior or errors.

If either of the specified files do not exist or are inaccessible to the user, `exch` will return an error. The command also requires write permissions to the directory containing the files. Care should be taken when using `exch` on files that are currently being accessed or modified by other processes, as this may lead to unexpected results or data corruption. There is no option to undo the exchange, unless the original files were backed up.

The `exch` command provides basic error handling. It typically checks if both files exist and if the user has the necessary permissions to modify them. If any error occurs, a relevant message is displayed, and the command exits with a non-zero status code.

The swapping operation relies on the atomic nature of the rename system call on most Unix-like systems. This minimizes the risk of data corruption due to interruptions during the swapping process. However, complete atomicity is not guaranteed, especially in networked file systems or under very high load.

The `exch` command has been available in several Unix-like systems for a long time. Its origin is somewhat obscure, but it has been used as a basic file manipulation utility, particularly in scripting, to exchange file content quickly without relying on temporary files or complex copy operations. Precise details of its development and standardization across different Unix versions are difficult to pinpoint, but it remains a convenient tool where direct file content swapping is needed.

mv(1), cp(1), diff(1)