Trap and SIGINT in bash

I am creating a script, using trap, that will count the number of times a user uses ctrl_c and then allows the user to finally quit on the 5th attempt.

#!/bin/bash

count=0

for i in 'seq 1 5';
do

trap ctrl_c SIGINT
((count=count+1))

done

echo $count

Not sure if I am on the right track for this one. Or if I am using trap with SIGINT correctly. When I run this script I just get 1. I do not get the option to try ^C multiple times.

I think I see the issue you are having understanding trap. Below is an example using your code.

There are a few articles about how trap works here on StackOverflow. For example https://stackoverflow.com/questions/14197470/how-does-trap-kill-work-in-bash-on-linux

trap is described here https://www.gnu.org/savannah-checkouts/gnu/bash/manual/html_node/Bourne-Shell-Builtins.html

There are many examples of its use on GitHub too. I hope one of them helps if my example isn't clear. https://github.com/search?q=trap+SIGINT+language%3AShell&type=code&ref=advsearch

I think the cleanup examples are most helpful.

#/bin/bash

ctrl_c() {
  ((count=count+1))
  [[ count == 5 ]] && (
    echo $count
    exit
  )
}

count=0
trap ctrl_c SIGINT
# do stuff

</details>



# 答案2
**得分**: 0

以下是您要翻译的内容：

No, it's `trap [-lp] [[arg] sigspec]` per [man 1 bash](https://www.man7.org/linux/man-pages/man1/bash.1.html)  (or think of it as `trap command_to_run signal[s]`) So can set 2 `trap` instructions to count the &lt;kbd&gt;Ctrl+C&lt;/kbd&gt; `SIGINT` signals and then to print `count` when the program terminates, (1) a `trap` for &lt;kbd&gt;Ctrl+C&lt;/kbd&gt; to catch `SIGINT`and (2) to handle exit or termination (signals `EXIT` and `SIGTERM`) to output `count` at the end.  (see [man 7 signal](https://man7.org/linux/man-pages/man7/signal.7.html) for available signals and corresponding numbers or just type `trap -l` at the command line) 

The `-l` option causes the shell to print a list of the signal names and numbers (try it `trap -l` at the command line) and `-p` options allow you to display the list of commands associated with a `sigspec`. 

You can actually do something like the following where you just loop continually with `read` and a timeout, handing `&#39;q&#39;` to quit and relying on your `SIGINT` `trap` to increment the counter, e.g.

```bash
#!/bin/bash

declare -i count=0    ## may as well declare count as int type

## define 2 trap actions, one for script termination or exit
#  and one to increment count on Ctrl+C
trap &#39;printf &quot;count: %d\n&quot; &quot;$count&quot;&#39; SIGTERM EXIT
trap &#39;count=$((count + 1))&#39; SIGINT

## output simple directions to tell the user what to do
printf &quot;type &#39;q&#39; to quit or Ctrl+C to increment count\n&quot;

while :   ## loop continually
do
  read -r -s -N 1 -t 1 resp;    ## read into resp with 1 sec timeout
  [ &quot;$resp&quot; = q ] &amp;&amp; break      ## if &#39;q&#39; entered, break loop
done

(of course, you can simply output count after you exit the loop, but setting two trap instructions provides an additional way to handle it and demonstrates setting multiple traps)

Example Use/Output

Where we hit <kbd>Ctrl+C</kbd> 5 times before pressing 'q',

$ bash trapcount.sh
type 'q' to quit or Ctrl+C to increment count
count: 5

See What Is Happening

You can also write a simple function that is used as the trap action that will indicate <kbd>Ctrl+C</kbd> was pressed and provide the current count. For example:

#!/bin/bash

declare -i count=0      ## may as well declare count as int type

increment_count() {     ## simle function to use as trap action
  count=$((count + 1))  ## incement and output count
  printf "Ctrl+C handled, count: %d\n" "$count"
}

## define 2 trap actions, one for script termination or exit
#  and one to increment count on Ctrl+C
trap 'printf "count: %d\n" "$count"' SIGTERM EXIT
trap increment_count SIGINT

## output simple directions to tell the user what to do
printf "type 'q' to quit or Ctrl+C to increment count\n"

while :   ## loop continually
do
  read -r -s -N 1 -t 1 resp;    ## read into resp with 1 sec timeout
  [ "$resp" = q ] && break      ## if 'q' entered, break loop
done

Example Use/Output

Same 5 <kbd>Ctrl+C</kbd> before 'q':

$ bash trapcount2.sh
type 'q' to quit or Ctrl+C to increment count
Ctrl+C handled, count: 1
Ctrl+C handled, count: 2
Ctrl+C handled, count: 3
Ctrl+C handled, count: 4
Ctrl+C handled, count: 5
count: 5

That provides a bit better feedback.

Let me know if you have questions.

#!/bin/bash

declare -i count=0    ## may as well declare count as int type

## define 2 trap actions, one for script termination or exit
#  and one to increment count on Ctrl+C
trap 'printf "count: %d\n" "$count"' SIGTERM EXIT
trap 'count=$((count + 1))' SIGINT

## output simple directions to tell the user what to do
printf "type 'q' to quit or Ctrl+C to increment count\n"

while :   ## loop continually
do
  read -r -s -N 1 -t 1 resp;    ## read into resp with 1 sec timeout
  [ "$resp" = q ] && break      ## if 'q' entered, break loop
done

$ bash trapcount.sh
type 'q' to quit or Ctrl+C to increment count
count: 5

#!/bin/bash

declare -i count=0      ## may as well declare count as int type

increment_count() {     ## simle function to use as trap action
  count=$((count + 1))  ## incement and output count
  printf "Ctrl+C handled, count: %d\n" "$count"
}

## define 2 trap actions, one for script termination or exit
#  and one to increment count on Ctrl+C
trap 'printf "count: %d\n" "$count"' SIGTERM EXIT
trap increment_count SIGINT

## output simple directions to tell the user what to do
printf "type 'q' to quit or Ctrl+C to increment count\n"

while :   ## loop continually
do
  read -r -s -N 1 -t 1 resp;    ## read into resp with 1 sec timeout
  [ "$resp" = q ] && break      ## if 'q' entered, break loop
done

$ bash trapcount2.sh
type 'q' to quit or Ctrl+C to increment count
Ctrl+C handled, count: 1
Ctrl+C handled, count: 2
Ctrl+C handled, count: 3
Ctrl+C handled, count: 4
Ctrl+C handled, count: 5
count: 5