A backslash followed by any other character maps to that character.
With the exception of case conversion, characters in the classes are in unspecified order.
The following examples are shown as given to the shell:
Create a list of the words in file1, one per line, where a word is taken to be a maximal string of letters.
Translate the contents of file1 to upper-case.
(This should be preferred over the traditional Unix idiom of ""tr a-z A-Z"", since it works correctly in all locales.)
Strip out non-printable characters from file1.
Remove diacritical marks from all accented variants of the letter e:
"tr "[=e=]" "e""
.Fx implementations of tr did not order characters in range expressions according to the current locales collation order, making it possible to convert unaccented Latin characters (esp. as found in English text) from upper to lower case using the traditional Unix idiom of ""tr A-Z a-z"". Since tr now obeys the locales collation order, this idiom may not produce correct results when there is not a 1:1 mapping between lower and upper case, or when the order of characters within the two cases differs. As noted in the EXAMPLES section above, the character class expressions "[:lower:]" and "[:upper:]" should be used instead of explicit character ranges like "a-z" and "A-Z".
System V has historically implemented character ranges using the syntax "[c-c]" instead of the "c-c" used by historic BSD implementations and standardized by POSIX. System V shell scripts should work under this implementation as long as the range is intended to map in another range, i.e., the command ""tr [a-z] [A-Z]"" will work as it will map the [ character in string1 to the [ character in string2. However, if the shell script is deleting or squeezing characters as in the command ""tr -d [a-z]"", the characters [ and ] will be included in the deletion or compression list which would not have happened under a historic System V implementation. Additionally, any scripts that depended on the sequence "a-z" to represent the three characters a, - and z will have to be rewritten as "a\-z".
The tr utility has historically not permitted the manipulation of NUL bytes in its input and, additionally, stripped NULs from its input stream. This implementation has removed this behavior as a bug.
The tr utility has historically been extremely forgiving of syntax errors, for example, the -c and -s options were ignored unless two strings were specified. This implementation will not permit illegal syntax.
The tr utility conforms to -p1003.1-2001.
It should be noted that the feature wherein the last character of string2 is duplicated if string2 has less characters than string1 is permitted by POSIX but is not required. Shell scripts attempting to be portable to other POSIX systems should use the "[#*]" convention instead of relying on this behavior. The -u option is an extension to the -p1003.1-2001 standard.