Bash parse list for prime numbers. - bash

Question

I want to parse a list of hexas that i get from a file after parsing them for unique hexas and sorting them.
The list looks like this:
1 0xb6e38000
8 0xb6f66000
5 0xb6f69000
1 0xb6f6c000
3 0xb6fd4000
1 0xb6ff7000
2 0xb6ff8000
4 0xb6ffa000
1 0xb6ffb000
Now what i want to do, is refine it even more so that i get only the hexas with prime numbers in front, like this:
1 0xb6e38000
5 0xb6f69000
1 0xb6f6c000
3 0xb6fd4000
1 0xb6ff7000
1 0xb6ffb000
The command i have been using is this:
sort | uniq -c | grep " 1 0x"
But this command lists only the ones that appear only once in the file.
Can anyone help me "sort" this out ?

Answer 1

Original answer for prime numbers
As mentioned in the comments to the question, 1 is not prime, but in the description of desired output you list the lines starting with 1. However, if you actually want to filter out the lines with prime numbers in the first column, then the following script will help:
#!/bin/bash -
[ $# -gt 0 ] && source_file="$1"
: ${source_file:=/tmp/source-file}
function is_prime {
declare -i n="$1"
if [ $n -le 1 ]; then
return 1
elif [ $n -le 3 ]; then
return 0
elif [[ $(( $n % 2 )) == 0 || $(( $n % 3 )) == 0 ]]; then
return 1
fi
i=5
while [[ $(( $i * $i )) -le $n ]]; do
if [[ $(( $n % $i )) == 0 || $(( $n % ($i + 2) )) == 0 ]]; then
return 1
fi
(( i += 6 ))
done
return 0
}
while read -a line; do
# We accept only two or more columns
[ ${#line[#]} -ge 2 ] || continue;
if is_prime ${line[0]}; then
echo $line
else
echo >&2 "skipping ${line[*]} as ${line[0]} is not prime"
fi
done < "$source_file"
In this script we define is_prime function which returns zero (success status), if the first argument ($1) is a prime number. Non-zero means non-prime number. The algorithm is a version of this pseudo-code translated into Bash.
Then we read $source_file line by line with the while loop where we put the columns into the line array: read -a line. Then we check if is_prime ${line[0]} command exits with a success code (zero) and output the line if it is. Otherwise, we print a message to the standard error (echo >&2).
The script accepts optional argument for the source file path. It assigns $source_file to /tmp/source-file, if the first argument is missing.
Script usage
Save the above-mentioned code in script.sh file.
Call bash script.sh /path/to/source-file >filtered 2>errors
Examine the contents of filtered and errors files. The first will contain the lines filtered out from the source file.
The output files will look like the following:
filtered
5 0xb6f69000
3 0xb6fd4000
2 0xb6ff8000
errors
skipping 1 0xb6e38000 as 1 is not prime
skipping 8 0xb6f66000 as 8 is not prime
skipping 1 0xb6f6c000 as 1 is not prime
skipping 1 0xb6ff7000 as 1 is not prime
skipping 4 0xb6ffa000 as 4 is not prime
skipping 1 0xb6ffb000 as 1 is not prime
Update for odd numbers
i sould have mentioned this from the start, i need odd number lines to
show up, not prime. My bad. – biotic
It's easy to detect if a number is odd with an expression like if [[ $(( $n % 2 )) != 0 ]]. The expression checks if the remainder by 2 is not equal to zero, i.e. applies the modulo operation. If the remainder is zero, then the number is even, otherwise odd, of course.
The full script:
#!/bin/bash -
[ $# -gt 0 ] && source_file="$1"
: ${source_file:=/tmp/source-file}
while read -a line; do
# We accept only two or more columns
[ ${#line[#]} -ge 2 ] || continue;
declare -i n=${line[0]}
if [[ $(( $n % 2 )) != 0 ]]; then
echo ${line[*]}
else
echo >&2 "skipping ${line[*]} as ${line[0]} is even"
fi
done < "$source_file"
As for above, you run bash script.sh /path/to/source-file >filtered 2>errors
Sample output:
filtered
1 0xb6e38000
5 0xb6f69000
1 0xb6f6c000
3 0xb6fd4000
1 0xb6ff7000
1 0xb6ffb000
errors
skipping 8 0xb6f66000 as 8 is even
skipping 2 0xb6ff8000 as 2 is even
skipping 4 0xb6ffa000 as 4 is even