sed open file code example

Example 1: how to use sed output to overwrite existin file

# Finds a specific string with regex and appends content
# overiding existing file. 
sed '/regex/a' <file> | tee <file>
# Example
sed '/\[task_concurrency\]/a 'execute=True'' carbon.cfg | tee carbon.cfg

Example 2: bash search and replace text in file

# Basic syntax using awk:
awk '{gsub(regex, substitution_text, $field#); print $0;}' input_file
# Where:
#	- gsub is a function that replaces every regular expression (regex)
#		match with substitution_text. 
#	- $field# is optional but can be used to specify a particular field
#		where gsub should operate. (This is useful if you want to 
#		restrict the substitutions to a specific column)

# Example usage:
awk '{gsub(" ","",$0); print $0;}' input_file
# This replaces every space " " with nothing "", thereby eliminating all
# whitespace from the file