Regex that would grep numbers after specific string

Try this:

grep -oP '(?<=ID: )[0-9]+' file

or:

perl -nle 'print $1 if /ID:.*?(\d+)/' file

sed -n '/ID: 54376/,${s/[^ 0-9]*//g;/./p}'

That will print only all numbers and spaces occurring after ID: 54376 in any file input.

I've just updated the above a little to make it a little faster with * and not to print blank lines after removing the non-{numeric,space} characters.

It addresses lines from regex /ID: 54376/ ,through the $last and on them s///removes all or any *characters ^not [^ 0-9]* then prints /any/ line with a .character remaining.

DEMO:

{
echo line 
printf 'ID: 54376\nno_nums_or_spaces\n'
printf '%s @nd 0th3r char@cter$ %s\n' $(seq 10)
echo 'ID: 54376'
} | sed -n '/ID 54376/,${s/[^ 0-9]*//g;/./p}'

OUTPUT:

 54376
1  03  2
3  03  4
5  03  6
7  03  8
9  03  10
 54376

There are many ways of doing this. For example:

1. Use GNU grep with recent PCREs and match the numbers after ID: :

   grep -oP 'ID:\s*\K\d+' file
   

2. Use awk and simply print the last field of all lines that start with ID:

   awk '/^ID:/{print $NF}' file
   

   That will also print fields that are not numbers though, to get numbers only, and only in the second field, use

   awk '($1=="ID:" && $2~/^[0-9]+$/){print $2}' file
   

3. Use GNU grep with Extended Regular Expressions and parse it twice:

   grep -Eo '^ID: *[0-9]+' file | grep -o '[0-9]*'
   

Use egrep with -o or grep with -Eo option to get only the matched segment. Use [0-9] as regex to get just numbers:

grep -Eo [0-9]+ filename

Using sed:

{
    echo "ID: 1"
    echo "Line doesn't start with ID: "
    echo "ID: Non-numbers"
    echo "ID: 4"
} | sed -n '/^ID: [0-9][0-9]*$/s/ID: //p'

The -n is "don't print anything by default", the /^ID: [0-9][0-9]*$/ is "for lines matching this regex" (starts with "ID: ", then 1 or more digits, then end of line), and the s/ID: //p is of the form s/pattern/repl/flags - s means we're doing a substitute, to replace the pattern "ID: " with replacement text "" (empty string) using the p flag, which means "print this line after doing the substitution".

Output:

1
4

Another GNU sed command,

sed -nr '/ID: [0-9]+/ s/.*ID: +([0-9]+).*/\1/p' file

It prints any number after ID: