🚀 go-pugleaf

Holas como simplifico este script bash... es decir como anido los 
for...que no me doy cuenta... El bash tiene funciones para procesar cadenas?

==================================================================
#!/bin/sh
i=1
for ano in 2003 2004 2005
do
for mes in January February March April 
do
        zcat $ano-$mes.txt.gz 1>/dev/null 2>/dev/null
        if [ $? != 0 ]; then
                echo "No existe $ano-$mes.txt.gz"
        else
                echo "Procesando $mes $ano"
                zcat $ano-$mes.txt.gz|egrep '^(From: .*[^<].*|Subject:.*)' >t.dat
                cat t.dat|perl -w filtro.pl >> $i.dat
                echo $i
        fi
done
cat $i.dat|./op_matriz >ad.$i.dat
i=`expr $i + 1`
echo "--------------"
for mes in February March April May 
do
        zcat $ano-$mes.txt.gz 1>/dev/null 2>/dev/null
        if [ $? != 0 ]; then
                echo "No existe $ano-$mes.txt.gz"
        else
                echo "Procesando $mes $ano"
                zcat $ano-$mes.txt.gz|egrep '^(From: .*[^<].*|Subject:.*)' >t.dat
                cat t.dat|perl -w filtro.pl >> $i.dat
                echo $i
        fi
done
cat $i.dat|./op_matriz >ad.$i.dat
i=`expr $i + 1`
echo "--------------"
for mes in March April May June 
do
        zcat $ano-$mes.txt.gz 1>/dev/null 2>/dev/null
        if [ $? != 0 ]; then
                echo "No existe $ano-$mes.txt.gz"
        else
                echo "Procesando $mes $ano"
                zcat $ano-$mes.txt.gz|egrep '^(From: .*[^<].*|Subject:.*)' >t.dat
                cat t.dat|perl -w filtro.pl >> $i.dat
                echo $i
        fi
done
cat $i.dat|./op_matriz >ad.$i.dat
i=`expr $i + 1`
echo "--------------"
etc... etc....
========================================================

Saludos Horacio....