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How to test the output only contains a specific string

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}') ]

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.

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).

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

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

Quote:

Originally Posted by syg00 (Post 5487883)

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

Quote:

Originally Posted by MadeInGermany (Post 5488186)

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

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