sub

The sub() function replaces the first occurrence of the pattern within the source string.

result = sub (pattern, replacement, sourcestring);
pattern Required. The regular expression pattern to search for.
replacement

Required. The replacement string.

sourcestring Required. The source string to search for the first occurrence of pattern.

The resulting string

newstring = sub("\n$", "", textstring)

In this example, the first occurrence of a trailing new line is replaced with nothing, effectively chopping it off.

For more information, please see gsub.