what is s and g in sed command
sed In some versions of sed, the expression must be preceded by -e to indicate that an expression follows. The s stands for substitute, while the g stands for global, which means that all matching occurrences in the line would be replaced. The regular expression (i.e. pattern) to be searched is placed after the first delimiting symbol (slash here) and the replacement follows the second symbol. Slash (/) is the conventional symbol, originating in the character for "search" in ed, but any other could be used to make syntax more readable if it does not occur in the pattern or replacement; this is useful to avoid "leaning toothpick syndrome".