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- If you want an easy
command-line based utility

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to treat text, you might like tr.

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What is tr about?

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Well, tr stands for translate,

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and it allows you to
translate sets of characters

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into other sets of characters.

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And it is useful for converting
uppercase into lowercase,

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or the other way around,

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or a completely different
set of characters.

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You typically use it in a pipe.

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So, "echo hello", send it to a pipe.

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Then you do your tr stuff,

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by using either [:lower:] or [:upper:],

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or [a-Z] [A-Z], or even [a-m] [n-z].

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Let me demonstrate.

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So I'm using echo hello | tr,

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followed by [:lower:] and [:upper:].

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And that is translating
the text that to receive

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from the pipe to uppercase.

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The structure of using
[:lower:] and [:upper:],

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which basically is a regular expression,

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is really a nice structure

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because it works with many languages,

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including languages that
have special characters

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that exist in languages like
French, or German, or Spanish,

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like accents, and so, below or above,

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or around the character, and so on.

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So, let's get started with echo hello |.

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And |, that's to tr,

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and then I'm using [a-z] [A-Z].

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There we go.

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This is translating
"hello" into uppercase.

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Now that's all nice, but
this [a-z] [A-Z] doesn't work

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unless it is a special accent,

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which occurs in many languages

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like Swedish, and German,
and Spanish, and so on.

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If you are working with
words in these languages,

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you might be better off using
[:lower:] and [:upper:].

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[:lower:] and [:upper:]
is doing exactly the same

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as [a-z] and uppercase [A-Z],

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but it will deal the right way

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with letters that are containing accents.

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You can even do funny things with [A-Z].

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What do you think of
this one for instance?

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[a-m] followed by [n-z]

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is translating "hello" into "uryyo".

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Everything up from A up to M

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is translated in a matching
character from N up to Z,

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and that's how you can use the tr utility.

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And in case you are
wondering, why is that useful?

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Well, this is something
that is useful in scripts,

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or any other environment
where you need to make sure

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that your words have a certain case.

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Then, tr is a useful utility.