Viewing/Editing files of fixed width format

In an earlier post, I described a way to load a file with lines of fixed-width format into R. Using RStudio (and the View function), it is easy to view the data. On the other hand, it is not easy to edit the file when it has lines of different format. My multifwf package has a read.multi.fwf function but not a write.multi.fwf to write changes back to the file. On top of that, it is not easy for someone unfamiliar with R to filter/subset the loaded data.


Reading a fixed-width log file can be very frustrating especially while you are troubleshooting. For example, look at three lines from a SOP log file:

09:20:05.034 < NOSLMT0000666    EVILCORP00010.77SomeClientId    SomeAccountId   
09:20:05.099 > OC000001BLMT0000666    EVILCORP00010.77SomeClientId    SomeAccountId   
09:20:13.421 < NOBLMT0000666 EVILCORP00001.10AnotherClientId AnotherAccountId

Confusing, right? And these lines are of a very simple protocol. At the place where I work, we have much longer messages (even longer than 300 characters). Imagine having to find a certain field in a 350 character message. And under pressure this can be hard even for experienced employees. It would definitely help to be able to view the message fields in a clear way. To be able to quickly and safely locate any field in a given line even if you are new to the message protocol. To be able to do queries and filter out any lines not needed.

Apart from reading a fixed-width log file, sometimes you might need to edit one. For example, you might want to replay a log file but only after changing some values.


A solution is to use Record Editor or its little brother reCsvEditor. Both of these editors can be used to view/edit fixed-width data files as long as they know how the data is laid out. This data layout can be in many formats called Copybooks. After some experimentation I decided to use the XML Copybook since it allows for multiple data layouts in a single file. This way a single XML file can hold the specs for all the message types of the protocol. Another reason behind this choice is that the XML examples of Record Editor were the most intuitive.

Having decided on the layout format, I only had to create one for each of the four protocols I work with. Of course, this is tedious and error prone and since I already have the message specs in CSV format), I decided to create a tool that converts CSV specs to the XML Copybook format.

Here’s a simplified version of the “ams PO Download.Xml” example that comes with Record Editor:

<?xml version="1.0" ?>
        RECORDTYPE="GroupOfRecords" LIST="Y" QUOTE="" RecSep="default">
        <RECORD RECORDNAME="ams PO Download: Detail" COPYBOOK="" DELIMITER="<Tab>"
                DESCRIPTION="PO Download: Detail" FILESTRUCTURE="Default" STYLE="0" RECORDTYPE="RecordLayout"
            LIST="N" QUOTE="" RecSep="default" TESTFIELD="Record Type" TESTVALUE="D1">
                <FIELD NAME="Record Type"  POSITION="1" LENGTH="2" TYPE="Char"/>
                <FIELD NAME="Pack Qty"     POSITION="3" LENGTH="9" DECIMAL="4" TYPE="Num Assumed Decimal (Zero padded)"/>
                <FIELD NAME="Pack Cost"    POSITION="12" LENGTH="13" DECIMAL="4" TYPE="Num Assumed Decimal (Zero padded)"/>
                <FIELD NAME="APN"          POSITION="25" LENGTH="13" TYPE="Num (Right Justified zero padded)"/>
                <FIELD NAME="Filler"       POSITION="38" LENGTH="1" TYPE="Char"/>
                <FIELD NAME="Product"      POSITION="39" LENGTH="8" TYPE="Num (Right Justified zero padded)"/>
                <FIELD NAME="pmg dtl tech key" POSITION="72" LENGTH="15" TYPE="Char"/>
                <FIELD NAME="Case Pack id" POSITION="87" LENGTH="15" TYPE="Char"/>
                <FIELD NAME="Product Name" POSITION="101" LENGTH="50" TYPE="Char"/>
        <RECORD RECORDNAME="ams PO Download: Header" COPYBOOK="" DELIMITER="<Tab>"
                DESCRIPTION="PO Download: Header" FILESTRUCTURE="Default" STYLE="0" RECORDTYPE="RecordLayout" LIST="N"
            QUOTE="" RecSep="default" TESTFIELD="Record Type" TESTVALUE="H1">
                <FIELD NAME="Record Type"     POSITION="1" LENGTH="2" TYPE="Char"/>
                <FIELD NAME="Sequence Number" POSITION="3" LENGTH="5" DECIMAL="3" TYPE="Num Assumed Decimal (Zero padded)"/>
                <FIELD NAME="Vendor"          POSITION="8" LENGTH="10" TYPE="Num (Right Justified zero padded)"/>
                <FIELD NAME="PO"              POSITION="18" LENGTH="12" TYPE="Num Assumed Decimal (Zero padded)"/>
                <FIELD NAME="Entry Date" DESCRIPTION="Format YYMMDD" POSITION="30" LENGTH="6" TYPE="Char"/>
                <FIELD NAME="Filler"          POSITION="36" LENGTH="8" TYPE="Char"/>
                <FIELD NAME="beg01 code"      POSITION="44" LENGTH="2" TYPE="Char"/>
                <FIELD NAME="beg02 code"      POSITION="46" LENGTH="2" TYPE="Char"/>
                <FIELD NAME="Department"      POSITION="48" LENGTH="4" TYPE="Char"/>
                <FIELD NAME="Expected Reciept Date" DESCRIPTION="Format YYMMDD" POSITION="52" LENGTH="6" TYPE="Char"/>
                <FIELD NAME="Cancel by date" DESCRIPTION="Format YYMMDD" POSITION="58" LENGTH="6" TYPE="Char"/>
                <FIELD NAME="EDI Type"       POSITION="68" LENGTH="1" TYPE="Char"/>
                <FIELD NAME="Add Date" DESCRIPTION="Format YYMMDD" POSITION="69" LENGTH="6" TYPE="Char"/>
                <FIELD NAME="Filler"         POSITION="75" LENGTH="1" TYPE="Char"/>
                <FIELD NAME="Department Name" POSITION="76" LENGTH="10" TYPE="Char"/>
                <FIELD NAME="Prcoess Type" DESCRIPTION="C/N Conveyable/Non-Conveyable" POSITION="86" LENGTH="1" TYPE="Char"/>
                <FIELD NAME="Order Type" POSITION="87" LENGTH="2" TYPE="Char"/>

It is easy to see that for each record type there’s a separate RECORD tag. Each RECORD has a FIELDS tag that contains the fields of the record type. For each field there’s a separate FIELD tag with NAME, POSITION, LENGTH and TYPE attributes. Finally each RECORD tag has a TESTFIELD and a TESTVALUE attributes. These two will help Record Editor decide which RECORD to use for parsing a line by comparing the value of the field in TESTFIELD with the value of TESTVALUE. When they are equal, the FIELDS of the RECORD will be used to parse the line.


Hence the following design:

  1. Print the XML part up to, and including, the opening RECORDS tag. The RECORDNAME attribute of the main RECORD tag should be the name of the protocol
  2. for each CSV file:
    1. add a RECORD tag with the RECORDNAME and DESCRIPTION attributes set to the protocol name followed by the CSV filename
    2. for each field:
      1. add a FIELD tag with the NAME and LENGTH attributes taken from the CSV and the POSITION set to the offset of the field. TYPE will be Char for every field.
  3. close the RECORDS and main RECORD tags.


Here’s a BASH implementation for the SOP protocol.

Step 1:

cat <<EOF
<?xml version="1.0" ?>
        RECORDTYPE="GroupOfRecords" LIST="Y" QUOTE="" RecSep="default">

Step 2:

for s in $*; do
cat <<EOF
            LIST="N" QUOTE="" RecSep="default" TESTFIELD="MessageType" TESTVALUE="$SPEC_NAME">

    awk '
    BEGIN {
        FS = ","
        f_position = 1
    NR != 1 {
        f_name = $1
        f_length = $2
        printf "\t\t\t\t<FIELD NAME=\"%s\"  POSITION=\"%d\" LENGTH=\"%d\" TYPE=\"Char\"/>\n", f_name, f_position, f_length
        f_position += f_length
    ' $s
cat <<EOF

And finally step 3:

cat <<EOF

The complete script can be found here. It includes options for the protocol name and header length.


To try out on SOP:

  1. Download reCsvEditor.
  2. git clone
  3. cd SOP
  4. ./ -H 15 -p “SOP log” *.csv > sop.xml
  5. Run reCsvEditor
  6. On the left part of the Open File window, select the sopsrv_2016_12_06.log found in the log directory of the SOP repo. Do not click the Open button yet.
  7. On the right part of the Open File window, select the Fixed Width tab.
  8. Select the sop.xml Copybook created in step 4.
  9. Click the Open button.

Fig 1: The Opened *sopsrv_2016_12_06.log* file

Notice that only a couple of lines are displayed correctly. This is because the SOP log we opened has lines of different formats. One line has an OC message while another a TR and for each message type there’s a different data layout. You can use the Layouts combobox to select the layout of the line you want to parse.

Fig 2: Changing layout

Clicking the small button on the left of the row will open a detail tab.

Fig 3: A detailed view of a line

It is also easy to filter lines. Click the filter button (with the horizontal arrows) to open the filter window.

Fig 3: Keeping only OC messages (filter)

Finally you can make changes and save them back to the original file!

For further info have a look at the locally installed help file. You can access it from Help menu.


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