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Nathan Milford
Asked: 2009-06-18 06:10:49 +0800 CST

Shell script to extract string from a file and return the next chars until a whitespace

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We have an application that grabs it's setup parameters from a file. I want to extract one or two statements from the startup string and present them as a nice table.

An example string would be -Dmysql.host=mysql1.company.com but it might also be an ipaddress or a machine name and not an fqdn.

I want locate the -Dmysql.host= but return the servername.

Any tips or pointers as to how to, once I've found the string "-Dmysql.host=" in the file, show everything to the next white space would be appreciated.

Perhaps there is a better method. I plan on running this on a dozen machines or so eventually to return a list of which application machines are configured to talk to which db machine at a glance.

Thanks you for your time.

scripting bash shell

3 Answers

  1. Best Answer

    Try this:

    grep mysql.host file.txt | sed -e 's/.*mysql.host=\(\S*\).*/\1/g'

    You should end up with a value that is the value of mysql.host. You can put the -D in the match also if you want, but I have left it out because it is a parameter to grep and you need to escape it.

    • 4

  2. From the information given, I would go about this by first splitting everything based on whitespace, and then split those tokens based on the = sign. Pure bash solution would be something like what follows. 

      foo="bar=baz boo=zip"
  for keyvalue in $foo; do
     key=${keyvalue%%=*} 
     value=${keyvalue##*=}
     echo $key $value
  done

    Since IFS is probably whitespace, the shell takes care of splitting based on the whitespace. You can then use Parameter (Variable) Expansion to handle spiting into key / value pairs based on the equals sign.

    • 1

  3. How about feeding the files to good old sed:

    $ echo foo  -Dmysql.host=mysql1.company.com -bar | grep -- "-Dmysql.host=" | sed -e 's/^.*-Dmysql.host=//' -e 's/ .*//'
mysql1.company.com

    So in your case you'd feed it the file like so:

    $ grep -- "-Dmysql.host=" FILENAME | sed -e 's/^.*-Dmysql.host=//' -e 's/ .*//'

    I realize there's a grep in there that sed could handle but this is just easier to write, sed can be awkward.

    • 0