How do I extract xml properties using shell scripts?

Question

I have already extracted the tag from the source document using grep but, now I cant seem to figure out how to easily extract the properties from the string. Also I want to avoid having to use any programs that would not usually be present on a standard installation.

$tag='<img src="http://imgs.xkcd.com/comics/barrel_cropped_(1).jpg" title="Don't we all." alt="Barrel - Part 1" />' 

I need to end up with the following variables

$src="http://imgs.xkcd.com/comics/barrel_cropped_(1).jpg" $title="Don't we all." $alt="Barrel - Part 1" 

Answer 1

You can use xmlstarlet. Then, you don't even have to extract the element yourself:

$ echo $tag|xmlstarlet sel -t --value-of '//img/@src' http://imgs.xkcd.com/comics/barrel_cropped_(1).jpg 

You can even turn this into a function

$ get_attribute() { echo $1 | xmlstarlet sel -t -o """ -v $2 -o """ } $ src=get_attribute $tag '//img/@src' 

If you don't want to reparse the document several times, you can also do:

$ get_values() { eval file=\${$#} eval $#= cmd="xmlstarlet sel " for arg in $@ do if [ -n $arg ] then var=${arg%%\=*} expr=${arg#*=} cmd+=" -t -o \"$var="\" -v $expr -o \""\" -n" fi done eval $cmd $file } $ eval $(get_values src='//img/@src' title='//img/@title' your_file.xml) $ echo $src http://imgs.xkcd.com/comics/barrel_cropped_(1).jpg $ echo $title Don't we all. 

I'm sure there's a better way to remove the last argument to a shell function, but I don't know it.

Answer 2

I went with dacracot's suggestion of using sed although I would have prefered if he had given me some sample code

src=`echo $tag | sed 's/.*src=["]\(.*\)["] title=["]\(.*\)["] alt=["]\(.*\)["].*/\1/'` title=`echo $tag | sed 's/.*src=["]\(.*\)["] title=["]\(.*\)["] alt=["]\(.*\)["].*/\2/'` alt=`echo $tag | sed 's/.*src=["]\(.*\)["] title=["]\(.*\)["] alt=["]\(.*\)["].*/\3/'` 

Answer 3

If xmlstarlet is available on a standard installation and the sequence of src-title-alt does not change, you can use the following code as well:

tag='<img src="http://imgs.xkcd.com/comics/barrel_cropped_(1).jpg" title="Don'"'"'t we all." alt="Barrel - Part 1" />' xmlstarlet sel -T -t -m "/img" -m "@*" -v '.' -n <<< "$tag" IFS=$'\n' array=( $(xmlstarlet sel -T -t -m "/img" -m "@*" -v '.' -n <<< "$tag") ) src="${array[0]}" title="${array[1]}" alt="${array[2]}" printf "%s\n" "src: $src" "title: $title" "alt: $alt" 

Answer 4

Since this bubbled up again, there is now my Xidel that has 2 features which make this task trivial:

• pattern matching on the xml

• exporting all matched variables to the shell

So it becomes a single line:

eval $(xidel "$tag" -e '<img src="{$src}" title="{$title}" alt="{$alt}"/>' --output-format bash)