$re = '/(?smi)^.*tag="[A-Z]_([A-Z]{2})_(\d{4}).*$/msi';
$str = '<?xml version="1.0"?>
-<PEGraphic gridSpaceY="100" gridSpaceX="100" bkgdImage="" gridColor="#333333" paperColor="#000000" width="19600" height="14200" version="5">
<Font height="120" name="Arial"/>
-<Polyline backFill="yes" backColor="#FFFFFF">
<Location right="6020" bottom="12445" left="6018" top="11741"/>
<Pen width="2" style="solid" color="#00FF00"/>
<Brush style="hollow" color="#00FF00"/>
<Point y="11741" x="6019"/>
<Point y="12445" x="6019"/>
</Polyline>
-<Polyline backFill="yes" backColor="#E0E0E0">
<Location right="3365" bottom="12835" left="3363" top="11741"/>
<Pen width="2" style="solid" color="#00FF00"/>
<Brush style="hollow" color="#00FF00"/>
<Point y="11741" x="3364"/>
<Point y="12835" x="3364"/>
</Polyline>
-<Polyline backFill="yes" backColor="#FFFFFF">
<Location right="4627" bottom="6800" left="4521" top="5100"/>
<Pen width="2" style="solid" color="#00FF00"/>
<Brush style="hollow" color="#00FF00"/>
<Datasource stepped="no" server="USFRPVMESPOLYOL" map="IP_DIMAP" field="VAL" tag="p_dc_1730"/>
-<Animation on="yes">
<AnimationRange color="#666666" image="" text="act sp" max="0" min="0" index="1"/>
<AnimationRange color="#00FF00" image="" text="act sp" max="1" min="1" index="2"/>
</Animation>
<Point y="5100" x="4627"/>
<Point y="6800" x="4627"/>
</Polyline>
-<Polyline backFill="yes" backColor="#FFFFFF">
<Location right="3719" bottom="4394" left="1918" top="3300"/>
<Pen width="2" style="solid" color="#00FF00"/>
<Brush style="hollow" color="#00FF00"/>
<Datasource stepped="no" server="USFRPVMESPOLYOL" map="" field="VAL" tag="P_DC_2103"/>
-<Animation on="yes">
<AnimationRange color="#666666" image="" text="act sp" max="0" min="0" index="1"/>
<AnimationRange color="#00FF00" image="" text="act sp" max="1" min="1" index="2"/>
</Animation>
<Point y="4394" x="3718"/>
<Point y="4098" x="3718"/>
<Point y="4098" x="1918"/>
<Point y="3300" x="1918"/>
</Polyline>
';
$subst = "CG $1($2)";
$result = preg_replace($re, $subst, $str, 1);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php