Shell Programming and Scripting

Got it yoda. Thanks again.

My above assumption was wrong as you have said. I have misunderstood the role of asterik * in regular expression.

In regular expression (unlike file pattern matching in shell) an asterik will match the preceding item (space in this case) zero or more times.
It is the asterik which did the trick of getting lines which didn't end with trailing space to be included (because of the 'zero times' property mentioned in the last sentence)



In the below mentioned file heroes.txt , the line batman has a trailing space

Code:

$ cat heroes.txt
jimihendrix
batman
katman
dogman
$

# The following returns only batman, because grep is looking for lines which end with man and at least one space.

Code:

$ grep "man[ ]$" heroes.txt
batman

# In the below attempt, both katman and dogman were also returned because the lines end with the pattern man followed by zero occurences of space

Code:

$
$ grep "man[ ]*$" heroes.txt
batman
katman
dogman

Hope my assumption is right this time.

Yes. Your assumption is correct John.

Just a minor note: There is no need to use [ ] since this is equivalent to a single space character. So both grep 'man[ ]*$' and grep 'man *$' match zero or more spaces after man

Actually, in the code segment shown above there was no trailing space after batman (but I added one when I quoted your text above).

The command:

Code:

grep "man[ ]$" heroes.txt

doesn't look for it looks for man followed by exactly one space at the end of the line. The asterisk you showed in your later example:

Code:

grep "man[ ]*$" heroes.txt

matches man followed by zero or more spaces at the end of the line. And, the commands:

Code:

grep "man[ ][ ]*$" heroes.txt
        and
grep "man  *$" heroes.txt
        and
grep -E "man +$"

(note two space characters after man in the second command) will all look for lines ending with man followed by one or more spaces at the end of the line.

Many systems have an egrep utility that is a synonym for grep with the -E option; some ancient systems may have egrep but not recognize -E as a valid option to grep.

Hope this helps.