Batch Rename Files

Bulk renaming is fast to do and awkward to reverse, so the decisions worth making are the ones that prevent a second pass rather than the ones that make the first pass quick.

Sort order is the first trap and the one that surprises people most. A sequence numbered 1 to 20 sorts as 1, 10, 11 and so on in almost every file browser, because the comparison is character by character. Padding numbers with leading zeros so that every number has the same width fixes it permanently, and it is the single most useful convention in bulk renaming.

Characters that are legal on one system and not another cause problems that only appear later, usually when a file is shared. Colons, slashes, question marks and asterisks are reserved on at least one common platform. Leading and trailing spaces are legal and invisible and break things quietly. Emoji and accented characters are usually fine now and still cause trouble in older tooling and in some archive formats. Sticking to letters, digits, hyphens and underscores costs nothing and avoids all of it.

Dates in filenames should be written year first, then month, then day. It is the only ordering where sorting alphabetically also sorts chronologically, and it removes the ambiguity between the day-first and month-first conventions that otherwise makes a shared folder unreadable to half its readers.

Extensions are not decoration. Changing a file's extension does not change its format, so renaming a PNG to .jpg produces a file that some programs open and others reject, and the failure is confusing because the name says one thing and the contents another. If the format needs to change, convert it rather than renaming it.

Two habits prevent most regret: check the preview against a file whose correct new name you already know before applying, and rename a copy when the originals are irreplaceable. Collisions are the last thing to watch, since two files that map to the same new name will either overwrite or fail, and neither outcome is one you want to discover afterwards.