That is not the reason at all. In fact you should read about (POSIX basic) regular expressions, because you obviously don't correctly understand how they work:
The asterisk ("*") makes the previous expression optional, but it doesn't match anything in itself. It means "zero or more occurrences of what comes before". Here is an example:
The regular expression "abcd" matches a fixed string, "a", followed by "b", followed by "c", followed by "d". Now, if you change it to "abc*d" its meaning changes to: "a", followed by "b" followed by zero or more occurrences of "c", followed by "d". Here is an example list of strings that would be matched by this expression:
"abd"
"abcd"
"abccd"
"abccccccd"
etc.
Now, in light of this, read your regexp again:
What you did by inserting the "*" after the "<" was to make the "<" optional. Instead of exactly one "<" you now match any number of "<", including zero (that makes it optional). But what you want is to match the "<", then anything that might precede a ":" including the ":" itself. To phrase it differently: a "<", then zeror or more occurrences of "something, followed by a ":", then what you already matched.
So, let us take you original regexp:
and change it to the specification above. First: something, followed by a ':" - or, more robustly, any number of any character save for a ":", followed by a ":" is:
Let us put that in:
Next, we need "zero or more" occurrences of this whole group" and therefore we need to first group it to be able to address it with a single asterisk, hence:
Note, that groups are numbered automatically, so you may need to replace "\1", "\2", etc. in your replacement string with other numbers maybe.
On a side note: you don't need the grep at all because sed can do that itself:
Change:
to
I hope this helps.
bakunin
Quote:
Originally Posted by bakunin
Actually: no. Analyse the regexp carefully, i will put in a few extra spaces for emphasis:
So you have: <, which is simply a (fixed string of one) character and at the end mis>, which is also a fixed string. This matches <{something}mis>, yes?
Now, let us get to the interesting part, the middle expression, which will match the {something}: inside the grouping we have [^:]*:. That means: zero or more non-":" characters, followed by a ":". So, it would match (list of examples):
Now, as we have grouped that and put an asterisk at the end, we can have OR can not have such an expression before the "mis". Hence we match (putting it all together:
you see from the last example that there is still room for making the regexp more specific, but i didn't want to confuse you with too much information at once. Maybe this is all the precision you need anyway - only you know your data and can know that. If you would need the additional precision to not match the last example you can do that:
The \{0,1\} works similar to the asterisk, but instead of zero or more occurrences it specifies zero or more but at most one occurrence (this sounds like i'm phrasing it more difficult than necessary but you can change the numbers so that other ranges of allowed occurrences are required).
I hope this helps.
bakunin
Thank you so much......Such a nice explanation and i am really learning from these detailed explanation.
How can this regex expression be used in sed command to fetch the values. Earlier i was using this cmd and when i am changing it with new regex exp i am getting some syntax errors
Also one more thing if a single line contains same element twice or any number of time (Not known), how can i get all values separated by any delimiter.
Hi
How to call a shell scripting through a Perl scripting? Actually I need some value from Shell scripting and passes in the Perl scripting. So how can i do this? (2 Replies)
Hi all,
I would like to start developping some good scripting skills. Do you think it would be best to start with shell scripting or Perl? I already got a fundation, really basics, in perl. but I am wondering what would be best to be good at first.
Can you please help me determine which one to... (14 Replies)
I just upgraded to Android 2.2 from 2.1. The GPS issue that was troublesome in 2.1 seems to have been fixed. Some of web browsing seems faster, but it could just be my connection is better today ;) Flash works in some browsers but not very good and it is too slow for Flash apps designed for... (0 Replies)
Gents,
I have been working in a Solaris/Unix environment for about 9 months. I took some linux classses online before getting the job. But, I am not very good at scripting. I want to learn how to script. Do you think that I should start with Shell scripting or Perl? I wanted to continue with... (2 Replies)
Hey I have a data in the file named as outputFile.txt. The data is in the format
123456,12345678912345,400,09/09/09,INACTIVE.
I want this output without commas ie
12345612345678912345400090909INACTIVE.
Please tell me what to do and clear explain all the terms, as I am new to it. (6 Replies)
Hi, if in a network there are lots of PCs connected with either windows or linux as operating system.Then what will be the shell script for the same and also if the PC has linux in it then we have to find if it is occupied or unoccupied.
If the PC has windows in it then we have to find if it is... (6 Replies)
Hi there
please have a look at the code..i want to create Using a named pipe. Run a find in the background starting in the working directory
While this is happening wait for input from the user to ask him which file to find.
If the user does not enter any data in 10 seconds ask the user again.... (1 Reply)