You can do this on the command line with in-place editing.

johngg@shiraz:~/perl/Monks > cat > gtype.txt
goat
grate
grip
johngg@shiraz:~/perl/Monks > ls gtype*
gtype.txt
johngg@shiraz:~/perl/Monks > perl -pi.BAK -e 's{^g}{};' gtype.txt 
johngg@shiraz:~/perl/Monks > ls gtype*
gtype.txt  gtype.txt.BAK
johngg@shiraz:~/perl/Monks > cat gtype.txt
oat
rate
rip
johngg@shiraz:~/perl/Monks > cat gtype.txt.BAK 
goat
grate
grip
[download]

I hope this is helpful.

Update: See "Command Switches" in perlrun for explanations of -e, -i and -p.