When i write below command, it selects “aapp”. but it should be “aap”. Because ‘*’ means zero or more ‘a’.’p’ means one p.
$ echo "aapple" | grep "a*p"
terminal screenshot
can somebody please explain the reason, why the grep not select as expected?
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5
Grep is line oriented, so it reads lines from input, and prints the entire line when any part of it matches the specified RE. Thus any input line containing a p will be printed with a*p.
$ echo "aapple" | grep "a*p"
aapple
$ echo "nothing special" | grep "a*p"
nothing special
If you only want to print the part that matches the RE, you can use the -o option, but then it will print multiple lines if the RE matches in multiple non-overlapping places:
$ echo "aapple" | grep -o "a*p"
aap
p
If you use the --color option, it will print these two parts of the line in red, giving what you see in your image.
3
You provided command works in this way. * mean it print if “a” is just right on next of “p”.
But if “a” is not just concatenate with “p” on right side, it only print “P”.
Terminal
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