What is the difference between (cp f1.txt f2.txt) & (less f1.txt > f2.txt) [duplicate]

Question

I know that both will copy data from f1.txt to f2.txt, but what is the real difference?

(cp f1.txt f2.txt) 

vs:

(less f1.txt > f2.txt)

Answer 1

The difference is that cp is far clearer to humans. That is one of the first things you should be optimizing for.

Using less in this way is so obscure, it's not really obvious that it works unless you try it out. The other answer points out that it doesn't work - if your file contains certain characters, and you expect the command to work without user interaction, e.g. as part of a script. This limitation is also obscure (at least I didn't think of it, despite having seen this behavior plenty of times).

less happens to be slower, one reason is it transfers data in smaller chunks. Run them under strace, I see less chunks 1023 bytes (1KiB - 1); cp chunks 64KiB.

Answer 2

less has been designed as a pager (e.g .with next page functionlity) for text files. As such it is less optimized for copying files than say cp (which has been designed to copy data), and might have a considerable overhead, thus lacking in performance.

For starters, cp won't ask you for confirmation when handling files that contain special (e.g. control) characters.

In your cp example, you need to run exactly one program (cp) .

In the less example, the less command actually only outputs the contents of the given file to stdout and your shell redirects the stdout into a new file, so you are actually running two programs (one output, and one input).

Answer 3

• The cp variant is faster because it doesn't dump f1.txt contents to the screen:

  $ time cp f1.txt  f2.txt
  
  real    0m0.002s
  user    0m0.004s
  sys     0m0.000s
  $ rm f2.txt
  $ time less f1.txt > f2.txt
  
  real    0m0.009s
  user    0m0.004s
  sys     0m0.000s
  

0.002 for cp vs 0.009 for less.

• cp can save some mode bits of the original file while less creates a new file with modes according to umask value:

(...) each destination file is created
with the mode bits of the corresponding source file, minus the
bits set in the umask and minus the set-user-ID and set-group-ID
bits.

• cp is shorter to type. Seriously, it matters when you spend most of your time in command line.

Answer 4

Going on a tangent here since you're asking about *.txt files, there's one slight benefit of using less, which is to use its pre-processing feature to "modify the way the contents of the file are displayed". A contrived example would be to output the contents of a compressed file to the output:

less compressed.txt.gz > uncompressed.txt

But of course, that can, and probably should, be better done by zcat -c compressed.txt.gz > uncompressed.txt.

Still, I'm guessing this can be practical for environments where the less pre-processing is standardized (check for the environment variable LESSOPEN, which usually points to a file /usr/bin/lesspipe.sh), so that scripts/commands do not need to be concerned with parsing the input file into the target file.

I've also found this link where it shows more uses cases. As mentioned above, check your Linux environment's /usr/bin/lesspipe.sh to see what are the variety of files that less can extract textual information from.