How to test the output only contains a specific string

Mike_Brown · 01-27-2016, 01:43 AM

I use following shell script

Revised code

Code:

    host_list="/home/campus27/zwang10/bin/hostlist"
HOSTS=`cat $host_list`
cp /dev/null hostlist_available
for line in $HOSTS
do 
ssh -o ConnectTimeout=1s $line true &>/dev/null
RESULT=$?
if [ $RESULT -eq 0 ] 
	then
	output=$(ssh -f $line "w" | tail -n+3 | awk '{print $1}')
	if [[ $RESULT -eq 0 ]] && [[ -z $output || $output == 'zwang10' ]]
		then
		echo $line
		echo $line >> hostlist_available
	fi
fi
done

I would like to do following:

**Under the condition that

Code:

[ $RESULT -eq 0 ]

holds,
either

Code:

 [ -z $(ssh -f $line "w" | tail -n+3 | awk '{print $1}') ]

or

Code:

$(ssh -f $line "w" | tail -n+3 | awk '{print $1}') only contains string "zwang10"

holds, we still continue the loop.**

The command

Code:

$(ssh -f $line "w" | tail -n+3 | awk '{print $1}') ]

will output like following cases:

Only one of my name

Code:

 zwang10

Several my names

Code:

 
   zwang10
   zwang10

Some others name

Code:

    jack
    jack
    ben

Other names and mine

Code:

    jack
    zwang10
    zwang10

How can test whether the output only contains my name `zwang10`?

Revised requirement

Code:

$output == 'zwang10'

only output yes when there is only one

Code:

zwang10

. However, I also want it will output yes when there are multiple zwang10's and no other names.

syg00 · 01-27-2016, 04:27 AM

You seem to be of aware numeric comparisons (and -z which is a string operator) in test, so just use the string comparison operator(s).

MadeInGermany · 01-27-2016, 03:39 PM

The shell string match [[ == ]] has a problem with exact line match.
That's why I'd use grep here

Code:

if ssh ... | fgrep -xq zwang10
then
 ... 
fi

For example it will not match zwang100

syg00 · 01-27-2016, 04:31 PM

Single "=" with enhanced test should work.
Yeah, I know, "==" makes more sense if you've done any real programming.

Mike_Brown · 01-27-2016, 08:09 PM

Quote:

Originally Posted by syg00

You seem to be of aware numeric comparisons (and -z which is a string operator) in test, so just use the string comparison operator(s).

Hello, I revised my problem

Mike_Brown · 01-27-2016, 08:09 PM

Quote:

Originally Posted by MadeInGermany

The shell string match [[ == ]] has a problem with exact line match.
That's why I'd use grep here

Code:

if ssh ... | fgrep -xq zwang10
then
 ... 
fi

For example it will not match zwang100

Hello, I revised my problem

MadeInGermany · 01-28-2016, 08:28 AM

Based on your revised code.

Code:

host_list="/home/campus27/zwang10/bin/hostlist"
HOSTS=`cat $host_list`

# open the output file for this block, with descriptor 3 (keep 1=stdout and 2=stderr)
for host in $HOSTS
do 
  if ssh -nx -o ConnectTimeout=1s "$host" true &>/dev/null
  then
    # No "ssh -f" # stay synchronous if we want to safely capture the output
    # "who" is faster than "w", and is without header
    # The last part of the pipe is the effective exit status
    # Instead of "command; if [ $? -eq 0 ]" you can directly use "if command"
    if ssh -nx "$host" "who" | awk '{print $1}' | fgrep -qx zwang10
    then
      echo "$host"
      echo "$host" >&3  # write to descriptor 3
    fi
  fi
done 3> hostlist_available
# end of the block; the redirected file is closed