mjhjmtu

I have a text file where the barcode is in column 18. I'm interested in removing the last 16 characters from a TCGA barcode for a long list of samples or alternatively I want to print only the first 12 characters in the string from column 18 to a new column.
The characters differ in each line of the file so I can not simply use the sed command to remove characters following a certain character.

For example: TCGA-2E-A9G8-01A-11D-A403-09 needs to be shorted to TCGA-2E-A9G8 and print the shorted ID in a new column

I've seen responses such as: echo "$string:0:-16" I'm very new to programing so i'm not sure how to automate this for a spreadsheet with over 300,000 lines and directed to a specific column

Using awk:

awk 'print substr($18,1,12)' input

This will print characters 1-12 of column 18. This assumes that your text file is separated by whitespace. Which it likely isn't.

For CSV:

awk -F, 'print substr($18,1,12)' input

Based on Steeldriver's comment for adding this output to a new column:

awk '$(NF+1) = substr($18,1,12) 1' input > output

Unfortunately this creates a new file. gawk can modify a file in place but your best bet is to create a new file and then remove the old file.