195

I have a file with the following contents:

<username><![CDATA[name]]></username>
<password><![CDATA[password]]></password>
<dbname><![CDATA[name]]></dbname>

and I need to make a script that changes the "name" in the first line to "something", the "password" on the second line to "somethingelse", and the "name" in the third line to "somethingdifferent". I can't rely on the order of these occurring in the file, so I can't simply replace the first occurrence of "name" with "something" and the second occurrence of "name" with "somethingdifferent". I actually need to do a search for the surrounding strings to make sure I'm finding and replacing the correct thing.

So far I have tried this command to find and replace the first "name" occurrence:

sed -i "s/<username><![CDATA[name]]><\/username>/something/g" file.xml

however it's not working so I'm thinking some of these characters might need escaping, etc.

Ideally, I'd love to be able to use regex to just match the two "username" occurrences and replace only the "name". Something like this but with sed:

<username>.+?(name).+?</username>

and replace the contents in the brackets with "something".

Is this possible?

2
  • 2
    Just note that pretty much any regexp-based solution, unless extremely contrived, will risk breaking any time the input format changes. Regexps are a poor choice for dealing with XML, SGML or derivates (which this looks to me).
    – user
    Jun 7, 2013 at 21:57
  • Approved! Consider using XQuery for example: w3schools.com/xquery/default.asp. This is the W3C standard for retrieving and manipulating XML content.
    – lgeorget
    Jun 7, 2013 at 22:01

7 Answers 7

331
sed -i -E "s/(<username>.+)name(.+<\/username>)/\1something\2/" file.xml

This is, I think, what you're looking for.

Explanation:

  • parentheses in the first part define groups (strings in fact) that can be reused in the second part
  • \1, \2, etc. in the second part are references to the i-th group captured in the first part (the numbering starts with 1)
  • -E enables extended regular expressions (needed for + and grouping).
  • -i enables "in-place" file edit mode
17
  • 5
    it leaves behind a backup file, with the name (original name) + "-E". Nov 13, 2015 at 5:32
  • 8
    On OSX i get 'sed: 1: "s/(<username>.+)name(.+ ...": \1 not defined in the RE'. I pasted the exact example from this question into a file. then i ran the command from this answer on that file. Maybe OSX has different syntax?
    – deweydb
    Jan 21, 2017 at 5:52
  • 2
    The gnu version of sed supports the "-E" parameter, but not official. It's not even mentioned in the manpage. If you wanna use the extended regex, you have to use the "-r" parameter instead. Sep 19, 2017 at 17:39
  • 6
    @deweydb According to this answer, you should use \( and \) instead of ( and ).
    – Zhang Buzz
    Nov 12, 2017 at 13:56
  • 6
    On OSX -i requires an "extension" with which you can use an empty string: sed -E -i '' Apr 12, 2020 at 1:45
25
sed -e '/username/s/CDATA\[name\]/CDATA\[something\]/' \
-e '/password/s/CDATA\[password\]/CDATA\[somethingelse\]/' \
-e '/dbname/s/CDATA\[name\]/CDATA\[somethingdifferent\]/' file.txt

The /username/ before the s tells sed to only work on lines containing the string 'username'.

0
12

If sed is not a hard requirement, better use a dedicated tool instead.

If your file is valid XML (not just those 3 XML-looking tags), then you can use XMLStarlet:

xml ed -P -O -L \
  -u '//username/text()' -v 'something' \
  -u '//password/text()' -v 'somethingelse' \
  -u '//dbname/text()' -v 'somethingdifferent' file.xml

The above will also work in situations which would be difficult to solve with regular expressions:

  • Can replace the values of the tags without specifying their current values.
  • Can replace the values even if they are just escaped and not enclosed in CDATA.
  • Can replace the values even if the tags have attributes.
  • Can easily replace just occurrences of tags, if there are multiple with the same name.
  • Can format the modified XML by indenting it.

Brief demonstration of the above:

bash-4.2$ cat file.xml
<sith>
<master>
<username><![CDATA[name]]></username>
</master>
<apprentice>
<username><![CDATA[name]]></username>
<password>password</password>
<dbname foo="bar"><![CDATA[name]]></dbname>
</apprentice>
</sith>

bash-4.2$ xml ed -O -u '//apprentice/username/text()' -v 'something' -u '//password/text()' -v 'somethingelse' -u '//dbname/text()' -v 'somethingdifferent' file.xml
<sith>
  <master>
    <username><![CDATA[name]]></username>
  </master>
  <apprentice>
    <username><![CDATA[something]]></username>
    <password>somethingelse</password>
    <dbname foo="bar"><![CDATA[somethingdifferent]]></dbname>
  </apprentice>
</sith>
6
$ sed -e '1s/name/something/2' \
      -e '3s/name/somethingdifferent/2' \
      -e 's/password/somethingelse/2' sample.xml

You can simply use addresses as in the number preceding "s" which indicates the line number.

Also the number in the end tells sed to replace the second match instead of replacing the first match.

5

You need to quote \[.*^$/ in the regular expression part of the s command and \&/ in the replacement part, plus newlines. The regular expression is a basic regular expression, and in addition you need to quote the delimiter for the s command.

You can pick a different delimiter to avoid having to quote /. You'll have to quote that character instead, but usually the point of changing the delimiter is to pick one that doesn't occur in either the text to replace or the replacement text.

sed -e 's~<username><!\[CDATA\[name\]\]></username>~<username><![CDATA[something]]></username>~'

You can use groups to avoid repeating some parts in the replacement text, and accommodate variation on these parts.

sed -e 's~\(<username><!\[[A-Z]*\[\)name\(\]\]></username>\)~\1something\2~'

sed -e 's~\(<username>.*[^A-Za-z]\[\)name\([^A-Za-z].*</username>\)~\1something\2~'
1

For replace the "name" word with the "something" word, use:

sed "s/\(<username><\!\[[A-Z]*\[\)name\]/\1something/g" file.xml

That is going to replace all the occurrences of the specified word.

So far all is outputted to standard output, you can use:

sed "s/\(<username><\!\[[A-Z]*\[\)name\]/\1something/g" file.xml > anotherfile.xml

to save the changes to another file.

1
Usage: sed [OPTION]... {script-only-if-no-other-script} [input-file]...

    -r, --regexp-extended
             use extended regular expressions in the script.

so to replace value in a properties file

sed -i -r 's/MAIL\=(.+)/MAIL\=user@mymail.com/' etc/service.properties 

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.