` - back close or reverse close
shift +tilder
?Command Expansion
cat > lspath.txt
/etc
^C
ls -l `cat lspath.txt` | grep .conf > etcconf.file
OR
ls -l $(cat lspath.txt)
another example using "du" command:
du -h `cat lspath.txt`
set | grep ETCDIR
ETCDIR=`ls -l /etc`
echo $ETCDIR ## to reserve the normal format, use echo "$ETCDIR"
netstat -ant | grep 443
### checking https status, if result is 1, it is running; if result is 0, https service is dead###
ssl_status=`netstat -ant | grep 443 | wc -l`
echo $ssl_status
Linux Bash Scripting - Command Substitution
原文：http://blade20.blog.51cto.com/7928919/1948001