Nested while loop

tlegend33 · 09-15-2014, 02:39 PM

I have two files:

hostname.out - which contains a list of host names
host_info.out - which contains some similar host names to hostname.out and some additional host names. These host names however are listed with FQDN.

What I'd like to do is generate a list of all hosts in hostname.out, then just those hosts from host_info.out that don't exist in hostname.out. I want to skip host names that are similar between the two files. Here's what I came up with but my syntax is incorrect:

Code:

cat hostname.out > host_pwd.out


while read line2
do
   while read line
   do
   if [[ "$line" =~ "$line2" ]]; then
   :
   else
   echo $line2 > host_pwd.out
   done < hostname.out
done < host_info.out

Any help would be appreciated.

Thanks.

allend · 09-15-2014, 06:16 PM

A couple of points on your code.

Quote:

echo $line2 > host_pwd.out

It is best to quote variables when using echo.
You probably want to use the >> redirection, so that lines are appended to the host_pwd.out file.
Also, you failed to add 'fi' to the end of the 'if .. else' block.

Perhaps this will achieve what you want.

Code:

cp hostname.out host_pwd.out

while read line; do
  if ! grep -q "$line" host_info.out ; then
    echo "$line" >> host_pwd.out
  fi
done < hostname.out

allend · 09-16-2014, 12:24 AM

I have had another think about this and perhaps this is more like what you want.

Code:

cp hostname.out host_pwd.out

while read line2; do
  flag=0
  while read line; do
    if (( ${#line} > 1 )) && [[ "$line2" =~ "$line" ]] ; then
      flag=1
      break
    fi
  done < hostname.out
  if (( $flag == 0 )); then
    echo "$line2" >> host_pwd.out
  fi
done < host_info.out

tlegend33 · 09-17-2014, 09:36 AM

Thanks for getting back to me. Also, thanks for pointing out the fi and >> portions. I clearly have rocks in my head at the end of the day. At any rate, the code you provided is still giving me every row from both files.

A simplistic example:

Code:

line=server1.internet.com
line2=server1-h1.internet.com

if [[ "$line2" =~ "$line" ]] ; then
      flag=1
echo $flag
      break
else
echo "not working"
    fi

not working

There's something up with the comparison of the two strings.

allend · 09-17-2014, 06:04 PM

If you want that the presence of "server1.internet.com" should not cause "server1-h1.internet.com" to appear in the output file then perhaps this will help.

Code:

if [[ "$line2" =~ "${line%%.*}" ]] ; then

The =~ binary operator uses the right hand side as a pattern to be matched in the left hand side. You can manipulate the pattern to be matched using bash parameter expansions as in the example shown above.
You can also use grep style regular expression syntax such as ^ for start of line, $ for end of line and . for character in the pattern.
So,

Code:

if [[ "$line2" =~ ^"${line%%.*}" ]] ; then

will force the match to occur only at the start of $line2