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Let's simplify a bit the regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows:

Let's simplify a bit the regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

The main issue from your regex (apart non needed complexity and readability) is that you use extra erroneous spaces.

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows:

Let's simplify a bit with a simpler regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows:

Let's simplify a bit the regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows:

If you are ok, let's simplify a bit with a unique regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows:

Let's simplify a bit with a simpler regex:

grep -E '^P [0-9]+ -?24\b' file2.txt 

No need:

• the use of cat | grep, it's a useless use of cat
• to use a multiple|regex here

If you think you can have more space than just one in your input, you can use one of:

• +
• [[:space:]]+ (POSIX character class)
• \s+ require -P aka PCRE switch of grep

The regular expression matches as follows: