awk define list code example

Example: awk: can't read value of a; it's an array name.

# Error:
awk: can't read value of a; it's an array name.

# Solution:
# This error usually comes up if you're trying to print the keys or 
# values from an awk array (i.e. dictionary) incorrectly. To do this 
# properly, you need to loop over the keys in your array.

# Example usage for printing keys:
awk '{ a[$1]=$2 } END { for (key in a) { print key } }' input_file
# Where:
#	- The above statements prints all keys in the awk array/dictionary
#		made from the input_file
#	- a[$1] is an array/dictionary in which the first column ($1) is 
#		used as the key and the second column ($2) is used as the value
#	- END indicates what to do after the first statement has finished 
#		running. Here we start a loop that loops through the keys in the
#		array and prints them. 

# Example usage for printing key values:
awk '{ a[$1]=$2 } END { for (key in a) { print a[key] } }' input_file
# Where:
#	- The above statements prints all key values in the awk 
#		array/dictionary made from the input_file