Question

I’ve been playing around with a little shell script to get some info out of a HTML page downloaded with lynx.

My problem is that I get this string: <span class="val3">MPPTN: 0.9384</span></td>

I can trim the first part of that using:

trimmed_info=`echo ${info/'<span class="val3">'/}`

And the string becomes: “MPPTN: 0.9384”

But how can I trim the last part? Seem like the “/” is messing up with the echo command… I tried:

echo ${finalt/'</span></td>'/};

Answer 1

The behavior of ${VARIABLE/PATTERN/REPLACEMENT} depends on what shell you’re using, and for bash what version. Under ksh, or under recent enough (I think ≥ 4.0) versions of bash, ${finalt/'</span></td>'/} strips that substring as desired. Under older versions of bash, the quoting is rather quirky; you need to write ${finalt/<\/span><\/td>/} (which still works in newer versions).

Since you’re stripping a suffix, you can use the ${VARIABLE%PATTERN} or ${VARIABLE%%PATTERN} construct instead. Here, you’re removing everything after the first </, i.e. the longest suffix that matches the pattern </*. Similarly, you can strip the leading HTML tags with ${VARIABLE##PATTERN}.

trimmed=${finalt%%</*}; trimmed=${trimmed##*>}

Added benefit: unlike ${…/…/…}, which is specific to bash/ksh/zsh and works slightly differently in all three, ${…#…} and ${…%…} are fully portable. They don’t do as much, but here they’re sufficient.

Side note: although it didn’t cause any problem in this particular instance, you should always put double quotes around variable substitutions, e.g.

echo "${finalt/'</span></td>'/}"

Otherwise the shell will expand wildcards and spaces in the result. The simple rule is that if you don’t have a good reason to leave the double quotes out, you put them.