zmv

Rename files lowercase to uppercase

$ zmv '(*)' '${(U)1}'

$ zmv '(*)' 'prefix_$1'

$ zmv '(*).txt' '$1.md'

$ zmv -n '*.jpg' 'photo_$((++n)).jpg'

$ zmv -n '(*)' 'new_$1'

$ zmv '(*.txt)' 'subdir/$1'

zmv [-finqQsvwW] [-C|-L|-M|-p program] [--] srcpat dest

zmv is a Zsh builtin for batch renaming files using pattern matching and replacement. It's more powerful than basic mv for complex renaming operations.
The source pattern uses Zsh extended globbing. Parenthesized groups are captured and available as $1, $2, etc. in the destination pattern. Zsh parameter expansion modifiers can transform captured text.
Common modifiers: ${(U)1} uppercase, ${(L)1} lowercase, ${(C)1} capitalize, ${1:t} tail (basename), ${1:h} head (directory).
zmv must be loaded first: autoload -U zmv

-n

Dry run, show what would be done

Force overwrite without prompting

Interactive, prompt before overwriting

Quiet, don't report errors

Force bare glob qualifiers on pattern

Symbolic link instead of move

Verbose, print each command

Pick out wildcard parts of pattern

Same as -w but with pattern replacement

Copy instead of move

Hard link instead of move

Move (default)

Use specified program instead of mv

zmv is Zsh-specific. It won't work in bash or other shells.
Always use -n (dry run) first to verify the operation before executing.
Patterns use Zsh globbing, which differs from regular expressions. Enable extendedglob (**setopt extendedglob**) for full pattern support.

mv(1), rename(1), mmv(1), zsh(1)