In this short config I'll show how to convert xlsx Excel format files to CSV using Gnumeric spreadsheet program. Gnumeric is for this job the best tool to use as it will save you plenty of time. Lets get started by installing Gnumeric:
FEDORA/REDHAT/CENTOS
# yum install gnumeric
DEBIAN/UBUNTU
# apt-get install gnumeric
First, let's assume that our Excel xlsx file is named myexcel.xlsx and it contains multiple tabs. To simply convert this file to CSV we can run the following command:
$ ssconvert myexcel.xlsx myexcel.csv

The above command will only convert first TAB of myexcel.xlsx file. To convert all TABs we need to use -S option. This will create a multiple files each corresponding to its relevant TAB within the original Excel myexcel.xlsx file.
$ ssconvert -S myexcel.xlsx myexcel.csv
$ ls
myexcel.csv.0   myexcel.csv.11  myexcel.csv.14  myexcel.csv.17  myexcel.csv.2   myexcel.csv.4  myexcel.csv.7  myexcel.xlsx
myexcel.csv.1   myexcel.csv.12  myexcel.csv.15  myexcel.csv.18  myexcel.csv.20  myexcel.csv.5  myexcel.csv.8
myexcel.csv.10  myexcel.csv.13  myexcel.csv.16  myexcel.csv.19  myexcel.csv.3   myexcel.csv.6  myexcel.csv.9
If from some reason you wish to use any other delimiter instead of comma use -O option to accomplish this task. In the next example we will convert myexcel.xlsx Excel file to semi-column separated file:
$ ssconvert -S -O 'separator=;' myexcel.xlsx myexcel.txt
The ssconvert command will try to guess output file format based on the file extension supplied as an argument. Make sure not to use csv extension for your output file when using -O option. Otherwise you will get the following error message:
The file saver does not take options