History facility

The following awk program roughly simulates the history facility of certain shells. A line containing only = re-executes the last command executed. A line beginning with = cmd re-executes the last command whose invocation included the string cmd. Otherwise, the current line is executed.

   $1 == "=" { if (NF == 1)
                   system(x[NR] = x[NR-1])
               else
                   for (i = NR-1; i > 0; i--)
                           if (x[i] ~ $2) {
                                   system(x[NR] = x[i])
                                   break
                           }
               next }
   

   /./         { system(x[NR] = $0) }