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5.9 Locale Considerations

TODO: fix following paragraphs (copied verbatim from ’bracket expression’ section).

TODO: mention locale support is heavily dependent on the OS/libc, not on sed.

The current locale affects the characters matched by sed’s regular expressions.

In other locales, the sorting sequence is not specified, and ‘[a-d]’ might be equivalent to ‘[abcd]’ or to ‘[aBbCcDd]’, or it might fail to match any character, or the set of characters that it matches might even be erratic. To obtain the traditional interpretation of bracket expressions, you can use the ‘C’ locale by setting the LC_ALL environment variable to the value ‘C’.

# TODO: is there any real-world system/locale where 'A'
#       is replaced by '-' ?
$ echo A | sed 's/[a-z]/-/'
A

Their interpretation depends on the LC_CTYPE locale; for example, ‘[[:alnum:]]’ means the character class of numbers and letters in the current locale.

TODO: show example of collation

# TODO: this works on glibc systems, not on musl-libc/freebsd/macosx.
$ printf 'cliché\n' | LC_ALL=fr_FR.utf8 sed 's/[[=e=]]/X/g'
clichX