Convert between Unicode Normalization Forms on the unix command-line

Python has unicodedata module in its standard library, which allow to translate Unicode representations through unicodedata.normalize() function:

import unicodedata

s1 = 'Spicy Jalape\u00f1o'
s2 = 'Spicy Jalapen\u0303o'

t1 = unicodedata.normalize('NFC', s1)
t2 = unicodedata.normalize('NFC', s2)
print(t1 == t2) 
print(ascii(t1)) 

t3 = unicodedata.normalize('NFD', s1)
t4 = unicodedata.normalize('NFD', s2)
print(t3 == t4)
print(ascii(t3))

Running with Python 3.x:

$ python3 test.py
True
'Spicy Jalape\xf1o'
True
'Spicy Jalapen\u0303o'

Python isn't well suited for shell one liners, but it can be done if you don't want to create external script:

$ python3 -c $'import unicodedata\nprint(unicodedata.normalize("NFC", "ääääää"))'
ääääää

For Python 2.x you have to add encoding line (# -*- coding: utf-8 -*-) and mark strings as Unicode with u character:

$ python -c $'# -*- coding: utf-8 -*-\nimport unicodedata\nprint(unicodedata.normalize("NFC", u"ääääää"))'
ääääää

You can use the uconv utility from ICU. Normalization is achieved through transliteration (-x).

$ uconv -x any-nfd <<<ä | hd
00000000  61 cc 88 0a                                       |a...|
00000004
$ uconv -x any-nfc <<<ä | hd
00000000  c3 a4 0a                                          |...|
00000003

On Debian, Ubuntu and other derivatives, uconv is in the libicu-dev package. On Fedora, Red Hat and other derivatives, and in BSD ports, it's in the icu package.