Tr

We can also use tr to delete characters from our text using the -d flag. Lets see that in action:

echo "Hello there world! What a beautiful day!" | tr -d 'aeiou '

Hllthrwrld!Whtbtfldy!

Now we removed every vowel and space from our text.

Other than the default translate function or the delete function of tr we also have a squeeze function available to us. This squeeze function is signified with the -s flag. The squeeze function will go and find repeated characters matching the list we supply and squeezing them down to one character. Lets see that squeeze action:

echo "Thiiiiisss is aaaaa llllliinneeee offfff texxxxxtttt." | tr -s 'aeiou'

Thisss is a lllllinne offfff texxxxxtttt.

You can see we squeezed the duplicate vowels down to a single character. We can also provide tr with a class of characters as opposed to a large list. Lets try this on the previous echo statement we made:

echo "Thiiiiisss is aaaaa llllliinneeee offfff texxxxxtttt." | tr -s '[:lower:]' '[:upper:]'

THIS IS A LINE OF TEXT.

This command squeezed any lower case letters for us and turned them into upper case letters.

Another function of tr is the complement function. We can think of complement as a function we can add onto any tr command to do the opposite of what we say. Lets see complement paired with a delete command:

echo "Hello there world! What a beautiful day!" | tr -cd 'aeiou '

eo ee o a a eauiu a

This deleted everything but the vowels from our text. It is worth noting that the end of our text has a endline character (\n) and this will be deleted as well unless we add it to our list of characters.

echo "Hello there world! What a beautiful day!" | tr -cd 'aeiou \n'

eo ee o a a eauiu a

That concludes all of the basic features of tr I am going to cover. If you feel like you want to know more ways to use tr I have included some useful tricks below.

Here are some useful ways to use tr in your scripting life.