为什么这个bash脚本无法通过$获得后台进程的pid！

Question

I have a script like that:

su lingcat -c PHPRC\=\/home\/lingcat\/etc\/php5\ 
PHP_FCGI_CHILDREN\=4\ \/usr\/bin\/php\-loop\.pl\ \/usr\/bin\/php5\-cgi\ \-b\ 
127\.0\.0\.1\:9006\ \>\>\/home\/lingcat\/logs\/php\.log\ 2\>\&1\ \<\/dev\/null\ \&\ 
echo\ \$\!\ \>\/var\/php\-nginx\/135488849520817\.php\.pid

This is working. But there is too many \\ in the script, they make the code unreadable. So, I wrote a new shell script:

#!/bin/sh
case "$1" in
'start')
        su biergaizi -c "PHPRC=/home/biergaizi/etc/php5 PHP_FCGI_CHILDREN=2 
/usr/bin/php-loop.pl /usr/bin/php-cgi -b /var/run/virtualhost/php5-fpm-biergaizi.test.sock >>/home/biergaizi/logs/php.log 2>&1 </dev/null & 
echo $! > /var/php-nginx/biergaizi.test.php.pid"
        RETVAL=$?
        ;;
'stop')
        su biergaizi -c "kill `cat /var/php-nginx/biergaizi.test.php.pid` ; sleep 1"
        RETVAL=$?
        ;;
'restart')
        $0 stop ; $0 start
        RETVAL=$?
        ;;
*)
        echo "Usage: $0 { start | stop }"
        RETVAL=1
        ;;
esac
exit

But /var/php-nginx/biergaizi.test.php.pid is empty.

What's wrong?

Answer 1

The .pid file is empty, because $! gets substituted by the shell executing your script, instead of the shell executing the commands you pass through su . And as there is no recently started background command in your script, it substitutes an empty string. So, shell started by su executes simply echo > /var/php-nginx/biergaizi.test.php.pid .

To prevent that, quote your command passed to su using single quotes, instead of double quotes. It is better to do that to the "stop" command as well. Like this:

su biergaizi -c 'PHPRC=/home/biergaizi/etc/php5 PHP_FCGI_CHILDREN=2 
                 /usr/bin/php-loop.pl /usr/bin/php-cgi -b /var/run/virtualhost/php5-fpm-biergaizi.test.sock >>/home/biergaizi/logs/php.log 2>&1 </dev/null & 
                 echo $! > /var/php-nginx/biergaizi.test.php.pid'

And this:

su biergaizi -c 'kill `cat /var/php-nginx/biergaizi.test.php.pid` ; sleep 1'

See http://www.gnu.org/software/bash/manual/html_node/Quoting.html for details.

Answer 2

try this:

Escape $ from $! , before passing to su -c .