SED substitutions

The format for the substitute command is as follows:

    [address1[ ,address2]]s/pattern/replacement/[flags] 

The flags can be any of the following:

• n replace nth instance of pattern with replacement
• g replace all instances of pattern with replacement
• p write pattern space to STDOUT if a successful substitution takes place
• w file Write the pattern space to file if a successful substitution takes

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