Shell Programming and Scripting

awk '
/^9/                    {L = 0      #### If any line starting with 9 then make variable named L's value to 0.
                        }
$0 ~ "^XYZ.*" PAT1      {           #### If any line is starting with XYZ and having PAT1(variable whose value is defined, will mention in next steps)
                         L = 1      #### Make the value of variable named L to 1.
                         print      #### print the spcific matched line which has matched the condition to TRUE above condition.
                        }
$0 ~ "^1" PAT2 && L                 #### If any line starts with 1 and then have PAT2variable whose value is defined, will mention in next steps) and value of L is NOT NULL then no action mentioned which means awk will print that specific line then.
                                    #### awk works on method of condition and action, so kis condition is TRUE and NO action is mentioned then it does the default action which is printing the current line.
' PAT1="7789" PAT2="7345" file      #### Mentioning the values of variables PAT1=7789 and PAT2=7345 and mentioning the Input_file as named file.