Get string between strings in bash

Question

I want to get the string between <sometag param=' and '>

I tried to use the method from Get any string between 2 string and assign a variable in bash to get the "x":

 echo "<sometag param='x'><irrelevant stuff='nonsense'>" | tr "'" _ | sed -n 's/.*<sometag param=_\(.*\)_>.*/\1/p'

The problem (apart from low efficiency because I just cannot manage to escape the apostrophe correctly for sed) is that sed matches the maximum, i.e. the output is:

 x_><irrelevant stuff=_nonsense

but the correct output would be the minimum-match, in this example just "x"

Thanks for your help

For structured data, use a tool which understands the structure. man xsltproc — tripleee
– tripleee, Commented Dec 19, 2012 at 5:41

Steve · Accepted Answer · 2012-12-19 06:09:03Z

3

You are probably looking for something like this:

sed -n "s/.*<sometag param='\([^']*\)'>.*/\1/p"

Test:

echo "<sometag param='x'><irrelevant stuff='nonsense'>" | sed -n "s/.*<sometag param='\([^']*\)'>.*/\1/p"

Results:

Explanation:

Instead of a greedy capture, use a non-greedy capture like: [^']* which means match anything except ' any number of times. To make the pattern stick, this is followed by: '>.
You can also use double quotes so that you don't need to escape the single quotes. If you wanted to escape the single quotes, you'd do this:

-

... | sed -n 's/.*<sometag param='\''\([^'\'']*\)'\''>.*/\1/p'

Notice how that the single quotes aren't really escaped. The sed expression is stopped, an escaped single quote is inserted and the sed expression is re-opened. Think of it like a four character escape sequence.

Personally, I'd use GNU grep. It would make for a slightly shorter solution. Run like:

... | grep -oP "(?<=<sometag param=').*?(?='>)"

Test:

echo "<sometag param='x'><irrelevant stuff='nonsense'>" | grep -oP "(?<=<sometag param=').*?(?='>)"

Results:

edited Dec 19, 2012 at 6:09

answered Dec 19, 2012 at 5:39

Steve

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2 Comments

Robby75 Over a year ago

Thanks, the grep-based solution is what I was looking for.

James T Snell Over a year ago

FYI: The last grep test expression doesn't execute with the grep implementation on OS X 10.11. It may not work on BSDs in general. It DOES work on Ubuntu. :)

aktivb · Accepted Answer · 2012-12-19 15:39:29Z

0

You don't have to assemble regexes in those cases, you can just use ' as the field separator

in="<sometag param='x'><irrelevant stuff='nonsense'>"

IFS="'" read x whatiwant y <<< "$in"            # bash
echo "$whatiwant"

awk -F\' '{print $2}' <<< "$in"                 # awk

answered Dec 19, 2012 at 15:39

aktivb

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