Combine multiple sed commands [duplicate]

Question

having the following file:

<tr class="in">
  <th scope="row">In</th>
  <td>1.2 kB/s (0.0%)</td>
  <td>8.3 kB/s (0.0%) </td>
  <td>3.2 kB/s (0.0%) </td>
</tr>
<tr class="out">
  <th scope="row">Out</th>
  <td>6.7 kB/s (0.6%) </td>
  <td>4.2 kB/s (0.1%) </td>
  <td>1.5 kB/s (0.6%) </td>
</tr>

I want to get the values between each second <td></td> (and save it to a file) like this:

8.3
4.2

My code so far:

# get the lines with <td> tags
cat tmp.txt | grep '<td>[0-9]*.[0-9]' > tmp2.txt

# delete whitespaces
sed -i 's/[\t ]//g' tmp2.txt

# remove <td> tag
cat tmp2.txt | sed "s/<td>//g" > tmp3.txt

# remove "kB/s (0.0%)"
cat tmp3.txt | sed "s/kB\/s\((.*)\)//g" > tmp4.txt

# remove </td> tag and save to traffic.txt
cat tmp4.txt | sed "s/<\/td>//g" > traffic.txt

#rm -R -f tmp*

How can I do this the common way? This code is really noobish..

Thanks in Advance, Marley

Answer 1

Use the -e option (if using GNU sed). From the manual:

e [command] This command allows one to pipe input from a shell command into pattern space. Without parameters, the e command executes the command that is found in pattern space and replaces the pattern space with the output; a trailing newline is suppressed.

If a parameter is specified, instead, the e command interprets it as a command and sends its output to the output stream. The command can run across multiple lines, all but the last ending with a back-slash.

In both cases, the results are undefined if the command to be executed contains a NUL character.

Note that, unlike the r command, the output of the command will be printed immediately; the r command instead delays the output to the end of the current cycle.

So in your case you could do:

cat tmp.txt | grep '<td>[0-9]*.[0-9]' \
| sed -e 's/[\t ]//g' \
-e "s/<td>//g" \
-e "s/kB\/s\((.*)\)//g" \
-e "s/<\/td>//g" > traffic.txt

You can also write it in another way as:

grep "<td>.*</td>" tmp.txt | sed 's/<td>\([0-9.]\+\).*/\1/g'

The \+ matches one or more instances, but it does not work on non-GNU versions of sed. (Mac has BSD, for example)

With help from @tripleee's comment below, this is the most refined version I could get which will work on non-GNU versions of sed as well:

sed -n 's/<td>\([0-9]*.[0-9]*\).*/\1/p' tmp.txt

As a side note, you could also simply pipe the outputs through each sed instead of saving each output, which is what I see people generally do for ad-hoc tasks:

  cat tmp.txt | grep '<td>[0-9]*.[0-9]' \
    | sed -e 's/[\t ]//g' \
    | sed "s/<td>//g" \
    | sed "s/kB\/s\((.*)\)//g" \
    | sed "s/<\/td>//g" > traffic.txt

The -e option is more efficient, but the piping option is more convenient I guess.