AWK

By default, whitespace as delimiter.

Action	Command
Print all columns separated by whitespace	awk '{print $0}' filename
Print first column separated by comma	awk -F "," '{print $1}' filename
Print second and third columns separated by colon	awk -F ":" '{print $2 $4}' filename
Print all columns except 2nd column separated by whitespace	awk '{$2=""; print $0}' filename
Print all columns except 2nd and 3rd column separated by whitespace	awk '{$2=$3=""; print $0}' filename

ln

Better use absolute pathname.

Action	Command
Create Soft Link	`$ ln -s /full/path/to/src /full/path/link(from)/file` Softlink is only possible across different partitions.
Create Hard Link	`$ ln /full/path/to/src /full/path/link(from)/file` * . and .. are hardliked to the current and parent directory resepectively. Linux don't allow users to create hard link to directory. * No hard link across different partitions.
When deleting original file to soft link.	The soft link will still exist as broken link.
When deleting original file to hard link.	The hard link will still exist. Can access to the content of the original file which is already deleted.
Soft linke is very useful to storage problem	The Partition 1 is almost full. The additional space for log directory in the partition 1. Then move all log files to new partition, delete the original log file. 2. Create a soft link (as the same name to the original log directory) in the partition 1 so that the link points the new log directory in the partiion 2.

Finding the number of columns in csv file


wc -l millionsong.txt
head -n 1 millionsong.txt

head -n 1 millionsong.txt | wc -c  # just count the letters in first row.
head -n 1 millionsong.txt | awk -F',' ' { print NF }'  # Right result

Chris IJ Hwang

Contents

Home

Data Science/Machine Learning related

Quantitative Finance Modeling and Analysis

Visualization

Math Finance

Others

AWK

ln

Finding the number of columns in csv file