Writting a script I wanted to replace all characters except alpha ([a-zA-Z]) with a line break. By definition, when using -c flag (set complement) tr is supposed to replace all characters that are not in the SET1 with the character specified in SET2. Nevertheless, it doesn't work as expected... Try this:

echo '[[:lower:]]' | tr -c '[a-zA-Z]' '\n'

Output I get:


As it can be seen it replaces columns but not square brackets, which it it is supposed to replace.

Can anyone clarify this?


tr doesn't intepret character classes in that regex style.

[a-zA-Z] is interpreted as a set of [, the range of characters from a to z and ].

Therefore its complement is the set of characters including all the characters but [, the range of characters from a to z and ].

That's why [ and ] aren't replaced.

To replace any non-alphabetic character, just specify a-zA-Z as the complement of the set to be replaced:

echo '[[:lower:]]' | tr -c 'a-zA-Z' '\n'
% echo '[[:lower:]]' | tr -c 'a-zA-Z' '\n'


  • incosistency everywhere :3 Thanks mate! – vanjadjurdjevic Nov 2 '15 at 18:35

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