Hi all,
I am a new start of Linux. Have some problem when read the manpage of grep.
If use
grep -w 'abc' file.txt, I got the match lins like:
abc xxx
xxx abc xxx
xxx abc
That's mean -w option match whole words. But when I read manpage, it tells "substring must either be at the beginning of the line" and "it must be either at the end of the line". Why does the above second line match?
Furthermore, in the manpage's regular expressions part, all talk about empty string.
"The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word. "
I only know '^$' can match a empty line, and '^a' match a line start with 'a', 'c$' match line end with 'c' and '\<abc\>' just like -w 'abc' which matchs whole word 'abc'. But how to unstand them for empty string?
Anybody can give example for the use of \b and \B, that will be great help!
Thanks!
Vincent
