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According to https://www.geeksforgeeks.org/rev-command-in-linux-with-examples/
rev command in Linux is used to reverse the lines characterwise.
e.g.
wolf@linux:~$ rev
Hello World!
!dlroW olleH
What is the example of application of rev in real life?
Why do we need reversed string?
The non-standard rev utility is useful in situations where it's easier to express or do an operation from one direction of a string, but it's the reverse of what you have.
For example, to get the last tab-delimited field from lines of text using cut (assuming the text arrives on standard input):
rev | cut -f 1 | rev
Since there is no way to express "the last field" to cut, it's easier to reverse the lines and get the first field instead. One could obviously argue that using awk -F '\t' '{ print $NF }' would be a better solution, but we don't always think about the best solutions first.
The (currently) accepted answer to How to cut (select) a field from text line counting from the end? uses this approach with rev, while the runner-up answer shows alternative approaches.
Another example is to insert commas into large integers so that 12345678 becomes 12,345,678 (original digits in groups of three, from the right):
echo '12345678' | rev | sed -e 's/.../&,/g' -e 's/,$//' | rev
See also What do you use string reversal for? over on the SoftwareEngineering SE site for more examples.
rev comes from), the rev and revpag commands were documented in the same man page. With pr, troff and xcan (no idea what that one is) as SEE ALSO, suggesting document preparation and rendering contexts. Possibly it was to do with printing on the other side of pages with mirrored fonts (like for embossing or something).
Dec 1, 2020 at 11:27
can man page in v8)
Dec 1, 2020 at 11:35
awk as a tool for building tools though, much like you build tools for doing specific things by means of shell scripts and C programs etc. The short awk program I show in this answer could be seen as a tool for extracting the last field of a tab-delimited file. This could later be combined with other tools to do something else.
As a specific example, rev is a useful tool to help reverse complement a DNA sequence, something often done in bioinformatics.
Remember that DNA is a double stranded polymer comprised of nucleotides. Generally DNA is modeled simply by the first letter of its nucleotides (A,C,G,T). If the "sequence" of one strand is known, the other strand is as well, since A always pairs with T, and C always pairs with G. Thus, a double stranded DNA sequence may be this:
ACGTGTCAT
TGCACAGTA
Another thing about DNA and the two strands - they have directionality, and are often "read" from the 5' end to the 3' end. The strands have antiparallel directionality, and so are read in opposite directions - see the diagram below.
5' ACGTGTCAT 3'
3' TGCACAGTA 5'
Now - it is often useful to determine one strand given the other, and since sequences can be quite long (thousands or millions of nucleotides in length), this is done programmatically. One convenient way to do this is using rev (and tr):
echo ACGTGTCAT | tr ACGT TGCA | rev
ATGACACGT
In the days before bidi-aware terminals (and even before UTF-8), it could have been used to display text files in Hebrew (Arabic was more involved because you needed to convert the characters into their presentation form), converting them from logical directionality to the physical one.
seftont command, but forget bidi... and if you happen to need to read some Hebrew file on your server, rev would help. Though I imagine this is pretty rare.
Dec 4, 2020 at 7:42