how can i search a pattern like atleast one alphabet and one digit and one special character in given file or string?
There may be better ways in better shells, but you didn't say, so I'm assuming a rudimentary shell.
STR1='hello123\&*'
# Count kinds of chars by removing them with sed and measuring how many were removed.
STR2=`echo "$STR1" | sed 's/[a-zA-Z]//g'`
LEN2=`expr "${#STR1}" - "${#STR2}"`
echo "$LEN2 alphabetic chars"
STR3=`echo "$STR1" | sed 's/[0-9]//g'`
LEN3=`expr "${#STR1}" - "${#STR3}"`
echo "$LEN3 digits"
STR4=`echo "$STR1" | sed 's/[^a-zA-Z0-9 \t]//g'`
LEN4=`expr "${#STR1}" - "${#STR3}"`
echo "$LEN4 specials"
$ ./script
5 alphabetic chars
3 digits
3 specials
$