This solution can be found in several programming languages including Bash
The lookahead process is part of regular expressions.
The lookahead process looks ahead in the string and sees if it matches the given pattern, but then disregard it and move on.
It is very useful when we want to go through the strings.
The lookahead process can be both positive and negative depending on the purpose.
Negative lookahead is indispensable if you want to match something not followed by something else and looks like this:
The string is the question q is analyzed and if it does not match and is not followed by s returns the result.
The positive lookahead it works the same way only now it is parsed if it corresponds to s.
The positive lookahead looks like this:
Let's look at a simple example of detecting the PAE option for the processor.
We can use this command but we will find a lot of information ...
In some cases, the resulting information can be taken using pipe and grep but they will be increasingly fragmented.
[root@desk mythcat]# cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 58 model name : Intel(R) Celeron(R) CPU G1620 @ 2.70GHz stepping : 9 ...
I will use the same command cpuinfo and we will look for the pae information in the flags.
All CPU flags can be found here.
Let's prove with internal lookahead to find the pae flag.
This result gives me additional information, namely that there are two cores.
[root@desk mythcat]# cat /proc/cpuinfo | grep -oP '(?='pae')...' pae pae
Do you have a question?