CODEWITHSUNDEEP
bashshellunix
Mickey Sweatt
Mickey Sweatt

Reputation: 177

Cat a file Multiple times Without A Loop

This is NOT a homework question, this is a question from an old exam, so anyone giving an answer will not be contributing to academic dishonesty. For those still skeptical, I am simply seeking what command I could use for this.

You have a file called one_mb which is exactly 1 megabyte in size. You want to create from it a file of exactly 128 megabytes in size. Please write a shell script to do this with at most 9 lines and no loops, if statements, recursion, or any other logic control structures. Each command, including parameters, must be less than 100 characters in length.

I began to research xarg, but could not figure out a good way to use it to accomplish this.

Upvotes: 10

Views: 6156

Answers (6)

mgarciaisaia
mgarciaisaia

Reputation: 15560

I think it would be enough with the constraints you have. You can define a function that takes an integer as parameter. If it's greater than 0, cats the file and calls the same function again, but with the parameter decreased.

Then you just call the function with the value needed, and you're done.

Good ol' recursion :)

(Sorry, too lazy for coding, and there are lots of other working answers, just wanted to avoid recursion being forgotten :))

Upvotes: -1

iamauser
iamauser

Reputation: 11469

dd oflag=append conv=notrunc if=/dev/zero of=one_mb bs=1MB count=127

This will retain the file content and add a bunch of "zero" records to make it 128 MB. Do

ls -ltrh one_mb

to check if it actually is 128MB, otherwise you might have to change the "count=127" parameter.

Upvotes: 2

Rain
Rain

Reputation: 363

Not sure if this counts, but this came to mind:

seq 1 128 | xargs -Inone cat one_mb >> 128_mb

No loops were used, just a pipe and xargs.

Upvotes: 12

Josh Cartwright
Josh Cartwright

Reputation: 801

Assuming bash, you can use a one-line brace expansion hack:

cat one_mb{,}{,}{,}{,}{,}{,}{,} > 128_mb

Upvotes: 20

paxdiablo
paxdiablo

Reputation: 881303

At 100 characters per command, you could reduce it quite a bit:

cat one_mb one_mb one_mb one_mb one_mb one_mb one_mb one_mb >mb8
cat mb8 mb8 mb8 mb8 >mb32
cat mb32 mb32 mb32 mb32 >mb128
rm -f mb8 mb32

Upvotes: 4

FatalError
FatalError

Reputation: 54551

The big hint here is that it can be "no more than 9 lines". Since 2^7 = 128, you just need to double the file's size 7 times:

cat one_mb one_mb > two_mb
cat two_mb two_mb > four_mb
...
cat 64_mb 64_mb > 128_mb

Upvotes: 4

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