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))}' `

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'.

Are you sure that the awk command says print and not printf? — Scott - Слава Україні, May 11 '19 at 04:26
That line's broken and never worked properly. It will die out with an Ambiguous error. (or Expression Syntax in tcsh). — , May 11 '19 at 05:53
No need for grep. Use lines=$(awk '/num_lines/ {print $2}' ../config.txt) or even lines=$(awk '$1=="num_lines" {print $2}' ../config.txt) — Chris Davies, May 12 '19 at 19:17

score 1 · Accepted Answer · answered May 13 '19 at 03:59

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)) }'
```
can be written
```
awk '/num_lines/ { printf("%d", int($2)) }' filename
```
As I mentioned above, int($2) 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))
```
is overkill. As far as I can tell,
```
printf("%d", $2)
```
and
```
print int($2)
```
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)}'; date
42Mon, May 13, 2019 12:00:00 AM
 
$ echo "num_lines   42" | awk '{print int($2)}'; 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.

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)}' ../config.txt ) works perfect (in bash). — Loibologic, May 13 '19 at 12:25

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

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