Terminal Friday: Patch and Diff

Two of the essential tools in software development are Patch y Diff. It is not a mystery how they work, but I think this will be an interesting post. 🙂

Both are very powerful, and this is just like touching the surface, they have more utilities and other functions. Basically with these two tools we can create version control,

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Diff

We refer to comparison, it compares an "original" file with the "new" one, and informs us of the differences that exist between them. This tool also allows us to create .patch files that we use to create patches for our programs.

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Patch

It is the command with which we literally "patch" our original file, adding and / or removing lines according to the instructions contained in the .patch file

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There is also vimdiff, which is a visual tool to apply patches without the need for a .patch file, since it compares "original" and "new" and on the same file it is possible to edit line by line or the entire document. This I won't explain but I think it deserves a mention.

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Example

Now the fun is. Example!

This is the case, we have a great script that asks for your name and your age, if you are over 18 it tells you that you can vote, otherwise it tells you that you cannot vote.

original.sh

#! / bin / bash echo "Enter your name:" read name echo "Enter your age:" read age if [[18 -lt $ age]] then echo "Hello $ name, you are $ old and you can vote!" else echo "Hello $ name, you are $ old and cannot vote ..." fi

Done, here is the running script:

So, as good users we are, we share our script with a friend :), but we get a message saying that it has a flaw, that when it is 18 it says that it cannot vote when it should.

Now we begin to correct the small error and make a few modifications ...

new.sh

#! / bin / bash maxAge = 18 echo "Enter your name:"; read name echo "Write your age:"; read age if [[$ maxAge -le $ age]]; then echo "Hello $ name, you are $ years old and you can vote!" else echo "Hello $ name, you are $ years old and you cannot vote ..." fi exit 0

Suppose the script is very heavy. So, in order not to send the whole script again, we create a .patch 😀

$ diff -u original.sh new.sh> patch.patch

And now we have our patch. Here's a view on Vim:

And to apply it we simply use the .patch file in the script to be patched. Here is called originalAmigo.sh, which is an exact copy of the script original.sh

$ patch originalFriend.sh <patch.patch

And this leaves us our file originalAmigo.sh So:

As you can see it is very easy to get the diffs and apply the patches. It's all from me.

Greetings people, we will read next Friday.