Shell Programming and Scripting

awk '{getline x<f;print x;getline x<f;print x;print;getline;print}' f=file1 file2

awk 'function prl() {getline x<f;print x}{prl();prl();prl();print;getline;print;getline;print}' f=file1 file2

awk '{for(i=1;i<=3;i++){if (getline x<f){print x}}
         print;for(i=1;i<5;i++){if (getline)print}}' f=file1 file2

nawk '  
NR==FNR{a[++i]=$1  ; next}
{b[++j]=$1 ; next}
END{ if (j>=i) {max=j}else{max=i}
for (z=1;z<=max;z+=2){
     printf "%s\n%s\n%s\n%s\n",a[z],a[z+1],b[z],b[z+1]
  }
}
' File1.txt File2.txt