bashgrepregular expression
I've a file named "test" that contains
linux
Unixlinux
Linuxunix
it's linux
l...x
now when i use grep '\<l.*x\>' , it matches :
linux
it's linux
l...x
but when i use grep '\<l*x\>' , it only matches:
l...x , but according to the reference guide,
when using * , The preceding item will be matched zero or more times, i.e it should match anything that starts with 'l' and ends with 'x'
Can anyone explain why ,it's not showing the desired result or if i've understood it wrong ?
() means «groupping» which means set a part of the string which can operate as 1 item, and for backrefference too.[] means symbols setSo if you use parenthesis just for single symbols the meaning is same. But usually it used for multisymbol strings like (cat|dog)
you need:
grep -P '\S\s{1,3}\S' infile
\s matches a whitespace-character, not only a space.
\S matches a non-whitespace-character
in your attempt, you are not limiting that before &after your matches should not be a whitespace.
to filter on space only and avoid using PCRE, you can do:
grep '[^ ] \{1,3\}[^ ]' infile
or to work on lines having leading/trailing 1~3spaces:
grep '\([^ ]\|^\) \{1,3\}\([^ ]\|$\)' infile
input data (cat -e infile):
0space$
1 spaces$
2 spaces$
3 spaces$
4 spaces$
3spaces$
4space$
3spaces $
4spaces $
output:
1 spaces$
2 spaces$
3 spaces$
3spaces$
3spaces $
Best Answer
notation (.*)
The * in the regular expressions .* and * is referring to a count, not characters per say, more exactly it means 'zero or more'. Furthermore, the . means 'any single character'.
So when you put them together you get 'zero or more of any characters'. For example strings like these:
Would be matched by
<l.*x>. The last one is important, it shows that the .* can match nothing too.notation (*)
The use of * alone as I said is a counter. So when you put it after a letter such as 'l' the * is saying 'zero or more of l'.
Notice if we grep for
l*x, this will matchl...x, but probably not for the reason you'd think.It's matching on the trailing 'x'. The 'l' has nothing to do with why this is getting matched, other than the fact that the 'x' is preceded by 'zero or more l's'.