AWK - weird difference between printf and sprintf when taking substr - unix

Question

it's been a while since I have used AWK, but now i have an XML file where I like to increase an Id for a specific column; so it's an excellent task for AWK.
In theory, to increase the Id, the line gets parsed, you fish out the Id into a variable, ++ it, and reconstruct the line to print to the resulting stream.
However, when I use the variable ( x = sprintf(...)) I got weird results, so I used printf to debug the thing. And now the weird part : printf dumps exactly the right Id, but the variable gets rubbish, although they have the same input & syntax ...
Must be somethinig really silly off course, but I can't put my finger on it.
All Ids are in the form :
<column name="Id" type="System.Int32">x</column>
This is the code :
#!/bin/ksh
cd /mnt/c/J/D/Work/GIT/Repos/SkillsNG/SkillsNG.WebTests/Snapshots
print -n "Snapshot name: "
read snapshot
defaultId=0
print -n "Start increasing from Id [$defaultId]":
read id
[[ "$id" = '' ]] && id=$defaultId
cat $snapshot | awk -F '>' 'BEGIN {process=0;} {
if (match($0, /SecurityPermissions/))
{process=1;}
else
{
if (!process)
{
# just dump all tables up to SecurityPermissions, no processing needed
print;
next;
}
}
if (match($1, /<column name="Id" type="System.Int32"/))
{
if(match($2,/[0-9]*/))
{
printf "param 1: %s\n", $1
printf "param 2: %s\n", $2
printf "Id value : %s\n", substr($2, 1, index($2,"\<")-1);
val = sprintf("%s", substr($2,1, index($2,"\<")-1));
printf "value in variable: %s\n", $val;
newval = strtonum(val);
printf "new: %s\n", $newval
}
}
else print $0;
}' > $snapshot.new
# mv $snapshot $snapshot.old
# mv $snapshot.new $snapshot
cd -
And this a simple test xml:
<snapshot culture="en-US">
<table name="[dbo].[SecurityPermissions]">
<row>
<column name="Id" type="System.Int32">1</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">1</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
<column name="Id" type="System.Int32">2</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">50</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
<column name="Id" type="System.Int32">3</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">51</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
<column name="Id" type="System.Int32">4</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">52</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
<column name="Id" type="System.Int32">5</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">53</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
<column name="Id" type="System.Int32">6</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">54</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
<column name="Id" type="System.Int32">7</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">56</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
<column name="Id" type="System.Int32">8</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">57</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
<column name="Id" type="System.Int32">9</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">77</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
<column name="Id" type="System.Int32">10</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">78</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
<column name="Id" type="System.Int32">11</column>
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">80</column>
<column name="Access" type="System.Int32">15</column>
</row>
</table>
</snapshot>
Result file :
<snapshot culture="en-US">
<table name="[dbo].[SecurityPermissions]">
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 1</column
Id value : 1
value in variable: <column name="Id" type="System.Int32"
new: <column name="Id" type="System.Int32"
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">1</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 2</column
Id value : 2
value in variable: 2</column
new: 2</column
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">50</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 3</column
Id value : 3
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">51</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 4</column
Id value : 4
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">52</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 5</column
Id value : 5
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">53</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 6</column
Id value : 6
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">54</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 7</column
Id value : 7
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">56</column>
<column name="Access" type="System.Int32">1</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 8</column
Id value : 8
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">57</column>
<column name="Access" type="System.Int32">3</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 9</column
Id value : 9
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">77</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 10</column
Id value : 10
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">78</column>
<column name="Access" type="System.Int32">15</column>
</row>
<row>
param 1: <column name="Id" type="System.Int32"
param 2: 11</column
Id value : 11
value in variable:
new:
<column name="GroupId" type="System.Int32">1</column>
<column name="Securable" type="System.Int32">80</column>
<column name="Access" type="System.Int32">15</column>
</row>
</table>
</snapshot>
As can be seen from the result file, the Id value (via printf) works correctly, but the same construct to a variable (via sprintf) produces garbage.
Anybody got an idea what is going on?
Thanks in advance.
Cheers,
DJ

Answer 1

First of all, you should not try to do these things with awk or sed or anything like that. XML is a complicated data-structure with all its ugliness connected to it. While a simple awk might do it now, it will fail all of a sudden and you will not know what hit you.
If you want to increment that particular value, you could use the following xmlstarlet command:
$ xmlstarlet ed --update '//table/row/column[#name="Id"]' -x ".+1" test.xml
It reads like this: xmlstarlet will (ed) edit the file test.xml by (--update) updating all nodes that match the XPath expression ('//table/row/column[#name="Id"]' :: all nodes column child of row child of of table with an attribute name equal to Id) and change its value with an XPath expression -x ".+1" (increment current value (.))
To answer your question: you obtain the unexpected results with awk because you reference some variables using $. Example:
val = sprintf("%s", substr($2,1, index($2,"\<")-1));
printf "value in variable: %s\n", $val;
In your first line, you compute the value of val but in the second line, you use $val. The latter actually returns the value of the field with number val. So if val=2, then $val will return $2, i.e. the content of the second field.