Combine multiple sed commands

regex, sed, shell

Solution

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.

Problem

Original source

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