Extract an attribute value from XML

Question

Using Bash,

File:

<?xml version="1.0" encoding="UTF-8"?>
<blah>
    <blah1 path="er" name="andy" remote="origin" branch="master" tag="true" />
    <blah1 path="er/er1" name="Roger" remote="origin" branch="childbranch" tag="true" />
    <blah1 path="er/er2" name="Steven" remote="origin" branch="master" tag="true" />

</blah>

I have tried the following:

grep -i 'name="andy" remote="origin" branch=".*\"' <filename>

But it returns the whole line:

<blah1 path="er" name="andy" remote="origin" branch="master" tag="true" />

I would like to match the line based on the following:

name="andy"

I just want it to return:

master

Answer 1

Use an XML parser for parsing XML data. With xmlstarlet it just becomes an XPath exercise:

$ branch=$(xmlstarlet sel -t -v '//blah1[@name="andy"]/@branch' file.xml)
$ echo $branch
master

Answer 2

With grep:

grep -Pio 'name="andy".*branch="\K[^"]*' file

• -P enable perl regular expressions (PCRE)
• -i ignore case
• -o print only matched parts

In the regex, the \K is a zero-width lookbehind to match the part before the \K, but to not include it in the match.

Answer 3

Use xmllint to extract the value of the attribute using XPath:

xmllint --xpath 'string(/blah/blah1[@name="andy"]/@branch)' file.xml

It's better to use an XML parser to process XML since the order of the attributes can change and line breaks could be inserted resulting in the name and branch attributes being in different lines of the file.

Answer 4

Using awk:

awk '/name="andy"/{ for (i=1;i<=NF;i++) { if ($i ~ "branch=") { sub(/branch=/, ""); gsub(/"/, ""); print $i } } }' input

This will find a line containing name="andy" and then loop through each field in that line. If the field contains branch= we will remove branch= and all double quotes and print the remainder of the field.

sub(/branch=/, "") is looking for a match of branch= and replacing it with "" (nothing)

gsub is similar except it will replace globally (all occurances instead of just the first occurance).

Answer 5

I think this works:

$ grep -i 'name="andy" remote="origin" branch=".*\"' <filename> | awk -F' ' '{print $5}' | sed -E 's/branch=\"(.*)\"/\1/'
master

The awk part makes sure only branch="master" is returned, the sed part gives back what's between the double quotes with a reference (the \1 matches the part between the parentheses).

Now I know there are a lot of people out here with far more knowledge on the art that is awk and sed, so I'm prepared for some criticism :-)

Answer 6

If you don't have access to xmllint or xmlstarlet on your machine. Make sure to transform your xml to one line before using grep like this

cat <filename> | tr -d '\n'

now you are sure that tags are not broken up on separate lines

| grep -Eo  "<blah1[>\ ][^<]+name=\"andy\"[^>]+."

will cut out (like in xpath /blah1[@name="andy"])

<blah1 path="er" name="andy" remote="origin" branch="master" tag="true" />

now

| grep  -oP "(?<=branch\=\")[^\"]*"

will return (like in xpath /@branch)

master

all together

cat <filename> | tr -d '\n'| grep -Eo  "<blah1[>\ ][^<]+name=\"andy\"[^>]+." | grep  -oP "(?<=branch\=\")[^\"]*"