Bash Script to Split Large CSV Files

At times I work with very large CSV files and, unfortunately, not all systems can handle massive file imports. In those cases, I need a quick and easy way to split up one massive CSV file into many smaller CSV files. I’ve written the bash script below to do just that. The approach is based on the one suggested by Mark Setchell on StackOverflow.

# Author: Daniel Ziegler (

#Accept number of rows to split and filename as command line argument

#Get filename and file extension (probably .csv or .txt)

#Extract first line of input file as header row
HDR=$(head -1 $FILENAME)

#split file into chunks based on the number of lines input


#loop through chunks and output to new files in the current directory. Output files will be named “filename-n.ext” where “filename” is the input file name and “.ext” is the extension of that file
for f in num*

#include the header row unless we’re looking at the first chunk which already includes the header row
if [ $n -gt 1 ]


rm $f



Usage is just ./ XXX filetosplit where “XXX” is the number of lines you want in each smaller file and “filetosplit” is the input CSV file you’re looking to split up.

You can download a Zip of this script here:


  • This script assumes that your input file starts with a header row. This header row will be repeated in each output file
  • Should work with any file type, I just use it for CSV files primarily
  • I can’t take any responsibility if this script breaks something! Check the code before you run it!

Parse a String with PHP’s preg_match_all()

Several times I’ve run into scenarios where I needed to essentially parse a string in PHP that wasn’t in a common format (JSON, CSV, tab-separated, etc.). Early on in my career I avoided regular expressions (RegEx) like the plague but a few years back I decided the time was right to embrace RegEx. Good thing I did, too, because with PHP’s preg_match_all() function, solving this requirement was a breeze

My scenario was, I’ve got the following string: Package #1 Box name: Medium Box : 6x4x3: W=1.4: Value=199.99: SKU=1 *  Mobile Phone 1.4lb; Package #2 Box name: Large Box : 10x7x5: W=0.7: Value=39.99: SKU=1 *  Phone Case 2.1lb;. This string is related to an order on an ecommerce store and it tells me that the best way to ship this order is in two separate boxes, once called “Medium Box” and the other called “Large Box.”

This string is not in an easy-to-parse format but it is consistent! What I needed to do was get everything between every occurrence of “Box Name: ” and the subsequent ” : “. Initially I considered using PHP’s substr() function in conjunction with strpos(). I’d use strpos() to work out where “Box Name: ” was, use strpos() again with an offset to look for the subsequent ” : “, adjust both those numbers, and feed that back into substr() as the start and end. What a pain. And, when I have a string that contains multiple boxes as my example does, I’m forced to loop and keep iterating up the offset. That could work, but not really a good solution.

Enter preg_match_all()! Three lines of code is all it took to prove it worked:

$comment = “Package #1 Box name: Medium Box : 6x4x3: W=1.4: Value=: SKU=1 * Samsung Mobile Phone 1.4lbs 1.4lb; Package #2 Box name: Large Box : 10x7x5: W=1.4: Value=: SKU=1 * Samsung Mobile Phone 1.4lbs 1.4lb;”;

preg_match_all(“/Box name: (.*?) : /”, $comment, $boxNames);


The result from the print_r() on the last row there is: Array ( [0] => Medium Box [1] => Large Box ). That’s exactly what I needed. I could, of course, use additional preg_match_all()’s to find other elements like the box dimensions, weight, etc.

preg_match_all() takes three parameters in this scenario: a regular expression that covers the start element to look for (“Box Name: “) as well as the end element to look for (” : “); a string, and an output variable. Note that this line isn’t written as $boxNames = preg_match_all(…);, instead $boxNames is the third parameter.

$boxNames becomes an array of values. The first element of that array ($boxNames[0]) is the full match (in this case $boxNames[0][0] = “Box Name: Medium Box : “ and $boxNames[0][1] = “Box Name: Large Box : “). The second element of the array ($boxNames[1]) is the internal strings ($boxNames[1][0] = “Medium Box” and $boxNames[1][1] = “Large Box”). That’s the one I wanted so that’s the one I used. The array will contain as many matches as preg_match_all() finds (hence the “_all”).


A tool like RegExr is useful here when putting together your expression. I’ve covered this in more detail previously.

Regular Expressions for Shipment Tracking Code Verification

I set up a tracking page recently for orders and realized that since we ship via 3 carriers (UPS, UPSMI, and USPS) I needed to sort out which API to call based on the tracking number (I didn’t want to force the user to remember the tracking method themselves when I could figure it out for them). Using some tracking number regular expressions I found at StackOverflow I compiled the following list. I’ll add more as I find them. I’ve tested all of them and they all seem to work for what I’ve needed.

UPS (1Z numbers)
\b(1Z ?[0-9A-Z]{3} ?[0-9A-Z]{3} ?[0-9A-Z]{2} ?[0-9A-Z]{4} ?[0-9A-Z]{3} ?[0-9A-Z]|[\dT]\d\d\d ?\d\d\d\d ?\d\d\d)\b

UPS Mail Innovations (UPSMI)

USPS (4 Types)


  1. UPSMI is a bit strange in the way tracking numbers are set up. The tracking number starts with “MI” followed by your 6 character numeric UPSMI account number (this is different than your UPS account number which normally ends with “TT”). After that, it’s up to you to determine your format for your tracking number. We’re using one of two 3-character alphabetical codes followed by either a 4 or 7 character numeric code (that’s the “(ABC[0-9]{7}|XYZ[0-9]{4})” you’ll see in the regex). While the “MI[0-9]{6}” part is standard, I recommend writing and testing your own suffix with RegExr.

UPS Mail Innovations Sorting Facilities Codes

UPS Mail Innovations (UPSMI) is a partnership between UPS and the USPS where UPS picks up from the shipper, sorts the packages at one of a number of sorting centers throughout the US, ships them to another sorting center closest to the package’s destination, then hands it off to the USPS at one of USPS’ BMC (Bulk Mail Centers, now called NDCs or Network Distribution Centers) or SCF (Sectional Center Facilities). USPS then handles delivery from there. The advantage is that for mid-sized to larger shippers, rates are equal to USPS Media Mail but delivery times are equal to First Class plus one day. I’ll likely write more about UPSMI integration with WorldShip and other applications later.

I recently set up a connection to UPS’ tracking API which works for UPSMI packages as well now but ran into an issue with the information being returned. For standard small-package tracking, UPS’ tracking API returns the city and state for each activity (pickup, sorting, destination, etc.) but for UPSMI I was simply receiving facility codes instead of city and state. It took a while to track down packages which went through each of UPSMI’s facilities, but I eventually did and managed to put together the following PHP array which can be used to convert the facility code to the correct city and state.

USPS BMCs and SCFs don’t return the facility code, so you’re stuck either simply saying “Bulk Mail Center” or “Sectional Center Facility”, or setting up another API to get tracking information from the USPS once the package leaves the UPSMI system.

  $miFacilities = Array(
“BMC” => “Bulk Mail Center”,
“SCF” => “Sectional Center Facility”,
“OHGRV” => “Urbancrest, OH”,
“GATLA” => “Atlanta, GA”,
“TNLVR” => “La Vergne, TN”,
“CAFNN” => “Fontana, CA”,
“NJLOG” => “Logan Township, NJ”,
“WAABU” => “Auburn, WA”,
“MNMEN” => “Mendota Heights, MN”,
“ILCST” => “Carol Stream, IL”,
“UTWVY” => “West Valley City, UT”,
“TXOLL” => “Coppell, TX”,
“NCDHM” => “Durham, NC”,
“CALEA” => “San Leandro, CA”,
“MOKCY” => “Kansas City, MO”,
“AZTOL” => “Tolleson, AZ”,
“CTWDS” => “Windsor, CT”,
“FLORO” => “Orlando, FL”,
“NYEDG” => “Edgewood, NY”

I hope it saves someone else out there some time!