Question

Its a interview question. Interviewer asked this “basic” shell script question when he understand i don’t have experience in shell scripting. Here is question.

Copy files from one directory which has size greater than 500 K to another directory.

I can do it immediately in c lang but seems difficult in shell script as never tried it.I am familiar with unix basic commands so i tried it, but i can just able to extract those file names using below command.

du -sk * | awk  '{ if ($1>500) print $2 }'

Also,Let me know good shell script examples book.

Answer 1

du recurses into subdirectories, which is probably not desired (you could have asked for clarification if that point was ambiguous). More likely you were expected to use ls -l or ls -s to get the sizes.

But what you did works to select some files and print their names, so let’s build on it. You have a command that outputs a list of names. You need to put the output of that command into the command line of a cp. If your du|awk outputs this:

Makefile
foo.c
bar.h

you want to run this:

cp Makefile foo.c bar.h otherdirectory

So how you do that is with COMMAND SUBSTITUTION which is written as $(...) like this:

cd firstdirectory
cp $(du -sk * | awk '{ if ($1>500) print $2 }') otherdirectory

And that’s a functioning script. The du|awk command runs first, and its output is used to build the cp command. There are a lot of subtle drawbacks that would make it unsuitable for general use, but that’s how beginner-level shell scripts usually are.