What does an '@' character mean in a csh script

Question

I'm translating a csh script to bash an came across a line that looks like

@ lines = `grep num_lines ../config.txt | awk '{printf("%d",int(2ドル))}' `

What does the '@' do here? I found some documentation stating that csh uses '@' for expressions. However, this looks like a normal variable assignment to me. When I run the grep and awk part of the code in bash the output is an integer with a preceding '%d', e.g. '%d 12045'.

• Scott - Слава Україні: Are you sure that the awk command says print and not printf?
• user313992: That line's broken and never worked properly. It will die out with an Ambiguous error. (or Expression Syntax in tcsh).
• Loibologic: @Scott You are right, it's printf indeed.
• Chris Davies: No need for grep. Use lines=$(awk '/num_lines/ {print 2ドル}' ../config.txt) or even lines=$(awk '1ドル=="num_lines" {print 2ドル}' ../config.txt)

Answer 1

Well, it’s impossible to know what the author of that script was thinking. But here are some observations:

• If the awk command, indeed, says printf, then it is printing the integer value of the second string on the input line.
• As roaima commented, and as I have been known to comment, awk is a very powerful program. You almost never need to run it in combination with grep, sed, or another awk. So

  grep num_lines filename | awk '{ printf("%d", int(2ドル)) }'

  can be written

  awk '/num_lines/ { printf("%d", int(2ドル)) }' filename

• As I mentioned above, int(2ドル) gives you the integer part of the second string on the input line. So, if the config file says num_lines foo, you will get 0. If it says num_lines 3.14, you will get 3. It seems unlikely that you would need to take such precautions with a well-formed configuration file.
• In any case,

  printf("%d", int(2ドル))

  is overkill. As far as I can tell,

  printf("%d", 2ドル)

  and

  print int(2ドル)

  are (almost) exactly equivalent.
• The one difference that I can identify is that the printf version doesn’t write a newline at the end:

  $ echo "num_lines 42" | awk '{printf("%d", 2ドル)}'; date
  42Mon, May 13, 2019 12:00:00 AM
   
  $ echo "num_lines 42" | awk '{print int(2ドル)}'; date
  42
  Mon, May 13, 2019 12:00:01 AM

  but this isn’t really relevant, since `...` strips off a trailing newline.
• You say "this looks like a normal variable assignment to me". But users of [t]csh know that it doesn’t allow

  variable=value

  you have to say

  set variable=value

  or

  @ variable=expr

  Of course a simple integer constant is a valid expr, so the author may simply be using @ instead of set because it’s shorter and they know that the value is an integer.

So the statement is setting the lines variable to the value of num_lines from ../config.txt.

• Loibologic: Thanks for the comprehensive answer! I did not know this convenient way to look for specific strings with awk. lines=$( awk '/num_lines/ {print int(2ドル)}' ../config.txt ) works perfect (in bash).