07. Transliterating text tr

The tr command is used as a character-based search and replace function.

Simple Bioinformatics

If you're a bioinformaticist, you may find the need to replace all T characters from a DNA strand to U's to obtain the corresponding mRNA strand. We can do this in a one-liner with the tr command.


In biology, each DNA strand has a corresponding strand. G's pair to C's and T's pair to A's. Can we use tr to find the corresponding strand?


Lowercase to Uppercase

You can use this function to map lowercase letters to uppercase.

$ echo 'what is up world?' | tr a-z A-Z

From standard in and to standard out

You may also use redirection to direct an input file and write to some output.

$ cat fox.txt
The quick brown fox jumped over the lazy dog.
$ tr 'aeiou' 'AEIOU' < fox.txt
ThE qUIck brOwn fOx jUmpEd OvEr thE lAzy dOg.
$ tr 'aeiou' 'AEIOU' < fox.txt > vowelsCappedFox.txt
# Output to vowelsCappedFox.txt

Deleting specific characters

With the -d option, we can delete specific characters from a string.

$ echo 'Removing all vowels' | tr -d 'aeiou'
Rmvng ll vwls

Squeezing text

We can eliminate repeated instances of a letter with the squeeze option, -s. This removes all repeated characters that occur in sequence.

$ echo '1111112222233333344444' | tr -s 123

Generating a secret message

We can generate an amateur secret message by mapping our lowercase characters to their inverse correspondence.

$ cat fox.txt | tr a-z zyxwvutsrqponmlkjihgfedcba
Tsv jfrxp yildm ulc qfnkvw levi gsv ozab wlt.

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