Merging files in Bash

Question

I had this homework assignment:

1. Create on the desktop a folder with your name.
2. Copy from your account [email protected] two files, "plik1.pdp" and "plik2.pdb".
3. Combine them to make a new file, "plik3.pdb", but they have to be in special order. The second file should be first, and then the first one.
4. Write down from the connected/combined "plik3.pdb" lines with "CA" to the new file "plik4.pdb".
5. In this new file, change the lines 1-240 from "1.00" to "0.00".

The following code is my solution:

cd Desktop
mkdir "name"
cd "name"
scp [email protected]:/home/XYZ plik[12].pdb
cat plik2.pdb plik1.pdb > plik3.pdb
grep 'CA' plik3 > plik4
sed -i -n 1,240p -e 's/1\.00/0\.00' plik4

Is it ok? Did I do anything wrong?

Answer 1

Overall it is close, but it won't work. Given that it's a homework assignment, you would possibly get points for trying, but if you ever intend to use bash scripting after school (and you should; it's very useful) do yourself a favor and set up a Linux test environment on your personal computer to play around with.

Only two things wrong that I see (though I didn't test it). In order of simplicity:

1. You stopped including the filename extensions in your last two commands. plik3.pdp and plik3 refer to two different files; extensions are not considered in any special way in Linux and are simply part of the filename.
2. Your scp command is wrong. I don't think it will do anything (just throw an error), but if it does anything it definitely won't be what you expect.

Try scp [email protected]:/home/XYZ/plik{1,2}.pdb ./

Note the added slash in the source name, and the inclusion of a target directory ./, which refers to the current working directory (in this case, Desktop/name).

By the way, the shell will expand the above to scp [email protected]:/home/XYZ/plik1.pdb [email protected]:/home/XYZ/plik2.pdb ./ Which gives you a hint on syntax if you need to copy multiple files that don't have the first part of the name in common.