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Objective: 1) Return a name value from an <a> and 2) assess a cell value from a number of HTML table rows, conditionally returning 0 or 1

I do curl -s http://[server-fqdn]/stats/servers?t=db | grep 'tr class="server" which returns a varying number of rows, as illustrated in the snippet. In this case, I list db servers.

Row snippet (NB: full row character count is between 2,000 and 2,150 characters)

<tr class="server"><td class=val><a name="srv_backend_3306/server"></a></td> [cut away] <td class=val>1d3h UP</td>

Challenge: Extract the value of name in the first <a> tag and assess the content of the <td class=val></td> (if it contains the word UP, return 0, else return 1).

I can extend my above described curl command, adding | cut -d\> -f3 | cut -d\" -f2 and I get the name - but how to get that other result? I have no unique identifier for that cell and using cut doesn't quite cut it due to dynamics in the table generation.

3
  • 3
    If the HTML is valid XML then you can use something like xmlstarlet to pick out the element value directly Commented Dec 17, 2020 at 9:51
  • There's also pup which is aimed at HTML
    – muru
    Commented Dec 17, 2020 at 10:03
  • You can check my answer below :)
    – Reda Salih
    Commented Dec 17, 2020 at 21:48

2 Answers 2

1

Here is a little snippet that was inspired by a StackOverflow answer that you can use with native bash, you will have one function to read the content of your input and then another to parse the dom content :

#!/bin/bash
cr=1
ac=""
read_dom () {
    local IFS=\>
    read -d \< ENTITY CONTENT
    local ret=$?
    TAG_NAME=${ENTITY%% *}
    ATTRIBUTES=${ENTITY#* }
    return $ret
}

parse_dom () {
    
    if [[ $TAG_NAME == "a" ]] ; then
    eval local $ATTRIBUTES
        ac=`cut -d "=" -f2  <<< "$ATTRIBUTES" | tr -d '"'`
    fi 
    if [[ $TAG_NAME == "td" && "$(cut -d= -f1 <<< $ATTRIBUTES)" == "class" && $CONTENT == *"UP"*  ]] ; then
        cr=0 
    fi
}

while read_dom; do
    parse_dom
done  <<< "$(curl -s http://[server-fqdn]/stats/servers?t=db | grep 'tr class="server")"
echo "<a> tag content : $ac"
echo "return value for <td> check : $cr"

Output :

<a> tag content : srv_backend_3306/server
return value for <td> check : 0
1
  • I like this approach, but I managed to come up with a solution, that works for me.
    – DavDav
    Commented Dec 18, 2020 at 9:45
0

Found a solution - it does the job, but feel free to suggest improvements ;)

#!/bin/bash
curl -s http://[server-fqdn]/stats/servers?t=db | grep 'tr class="server"' > hastats.html
for i in `cat hastats.html | grep 'tr class="server"' |  cut -d\> -f3 | cut -d\" -f2` ; do
grep $i hastats.html | ( ! grep -P " UP" -q)
echo $i $?
done

This returns e.g. srv_backend_3306 1 for that server, which means that it was established that in this particular row, there was an occurence of the word UP with a whitespace in front. In this context, I am certain that this particular word will either be absent, or be present exactly one time for each of these particular rows.

The ! grep -P ' UP' -q negates the returned error code, which normally would be '0' for 'occurence was found' - we want '1' returned for a particular reason.

Thanks for constructive input.

1
  • A few comments: i) avoid for i in $(cat file) (see Bash pitfall #1). You don't need it at here anyway: grep 'tr class="server"' hastats.html | cut .... ii) this will break very easily. What if you have .foo tr { ...} in embedded css? What if you have <div name=footr class="server"? iii) You only have lines matching the search pattern in hastats.html, why grep it again? iv) there is no need for -P in your grep. It just makes the code less portable and doesn't add anything.
    – terdon
    Commented Dec 18, 2020 at 13:04

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