Shell script to read flat file and replace xml values - shell

Question

I have a flat file like this:
File:
# Environment
Application.Env~DEV
# Identity
Application.ID~999
# Name
Application.Name~appname
An XML like this:
<name>Application/Env</name>
<value>XXX</value>
<name>Application/ID</name>
<value>000</value>
<name>Application/Name</name>
<value>AAA</value>
I'm looking for a script (awk, sed etc) to read the flat file and replace all of the data in the <value> tags in the xml with the data found after the ~ when the <name> tag matches the data before the ~. Ultimately the resulting XML will look like:
<name>Application/Env</name>
<value>DEV</value>
<name>Application/ID</name>
<value>999</value>
<name>Application/Name</name>
<value>appname</value>
Thanks for your help!

Answer 1

Using XMLStarlet, this would look something like the following:
#!/bin/bash
# usage: [script] [flatfile-name] <in.xml >out.xml
flatfile=$1
# store an array of variables, and an array of edit commands
xml_vars=( )
xml_cmd=( )
count=0
while read -r line; do
[[ $line = *"~"* ]] || continue
key=${line%%"~"*} # put everything before the ~ into key
key=${key//"."/"/"} # change "."s to "/"s in key
val=${line#*"~"} # put everything after the ~ into val
# assign key to an XMLStarlet variable to avoid practices that can lead to injection
xml_vars+=( --var "var$count" "'$key'" )
# update the first value following a matching name
xml_cmd+=( -u "//name[.=\$var${count}]/following-sibling::value[1]" \
-v "$val" )
# increment the counter used to assign variable names
(( ++count ))
done <"$flatfile"
if (( ${#xml_cmd[#]} )); then
xmlstarlet ed "${xml_vars[#]}" "${xml_cmd[#]}"
else
cat # no edits to do
fi
This will run a command like the following:
xmlstarlet ed \
--var var0 "Application/Env" \
--var var2 "Application/ID" \
--var var3 "Application/Name" \
-u '//name[.=$var0]/following-sibling::value[1]' -v 'DEV' \
-u '//name[.=$var1]/following-sibling::value[1]' -v '999' \
-u '//name[.=$var2]/following-sibling::value[1]' -v 'appname'
...which replaces the first value after the name Application/Env with DEV, the first value after the name Application/ID with 999, and the first value after the name Application/Name with appname.
A slightly less paranoid approach might instead generate queries like //name[.="Application/Name"]/following-sibling::value[1]; putting the variables out-of-band is being followed as a security practice. Consider what could happen otherwise if the input file contained:
Application.Foo"or 1=1 or .="~bar
...and the resulting XPath were
//name[.="Application/Foo" or 1=1 or .=""]/following-sibling::value[1]
Because 1=1 is always true, this would then match every name, and thus change every value in the file to bar.
Unfortunately, the implementation of XMLStarlet doesn't effectively guard against this; however, using bind variables makes it possible for an implementation to provide such precautions, so a future release could be safe in this context.

Answer 2

Using Perl and XML::XSH2, a wrapper around XML::LibXML:
#!/usr/bin/perl
use warnings;
use strict;
use XML::XSH2;
open my $IN, '<', 'flatfile' or die $!;
$XML::XSH2::Map::replace = { map { chomp; split /~/ } grep /~/, <$IN> };
xsh << 'end.';
open 1.xml ;
for //name {
set following-sibling::value[1]
xsh:lookup('replace', xsh:subst(., '/', '.')) ;
}
save :b ;
end.
I wrapped the XML into a <root> tag to make it well formed.