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(textutils.info)Translating

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Translating
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   `tr' performs translation when SET1 and SET2 are both given and the
`--delete' (`-d') option is not given.  `tr' translates each character
of its input that is in SET1 to the corresponding character in SET2.
Characters not in SET1 are passed through unchanged.  When a character
appears more than once in SET1 and the corresponding characters in SET2
are not all the same, only the final one is used.  For example, these
two commands are equivalent:

     tr aaa xyz
     tr a z

   A common use of `tr' is to convert lowercase characters to
uppercase.  This can be done in many ways.  Here are three of them:

     tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
     tr a-z A-Z
     tr '[:lower:]' '[:upper:]'

   When `tr' is performing translation, SET1 and SET2 typically have
the same length.  If SET1 is shorter than SET2, the extra characters at
the end of SET2 are ignored.

   On the other hand, making SET1 longer than SET2 is not portable;
POSIX.2 says that the result is undefined.  In this situation, BSD `tr'
pads SET2 to the length of SET1 by repeating the last character of SET2
as many times as necessary.  System V `tr' truncates SET1 to the length
of SET2.

   By default, GNU `tr' handles this case like BSD `tr'.  When the
`--truncate-set1' (`-t') option is given, GNU `tr' handles this case
like the System V `tr' instead.  This option is ignored for operations
other than translation.

   Acting like System V `tr' in this case breaks the relatively common
BSD idiom:

     tr -cs A-Za-z0-9 '\012'

because it converts only zero bytes (the first element in the
complement of SET1), rather than all non-alphanumerics, to newlines.