sed command in linux to replace a string code example

Example 1: ubuntu command line replace word in files

sed -i 's/original/new/g' file.txt

Example 2: linux replace string in all files

sed -i 's/old-text/new-text/g' input.txt

Example 3: sed replace in file

sed -i 's/foo/bar/g' hello.txt

Example 4: bash find and replace all files with specifc name with another file

find . -name "boom.txt" -exec cp ~/replace.txt {} \;

Example 5: sed replace with variable

For using match in sed replacement, just border it with '\(' and '\)':
echo Before123 | sed 's/Before\([0-9]*\)/\1After/g'
123After	# number is matched withtin '\( \)' and replaced in '\1'
Example with 2 match replacements
echo a_b | sed 's/\(^.*\)_\(.*$\)/first is \1 and \2 is after/g'