Originally Posted by bakunin

When you try to match strings with sed you need to distinguish between characters and metacharacters. Characters only match themselves, i.e.

Code:

sed -n '/a/p' /some/file

will print every (line containing an) "a" because /a/ matches only an "a" and nothing else.

But there are characters that do not match these same characters directly but influence the way other characters match something. These are called metacharacters and a "regular expression" usually consists of a mixture of characters and metacharacters. Here:

Code:

sed -n '/aa*z/p' /some/file

the expression searched for to print the line is /aa*z/ and the asterisk makes the "a" in front of it optional: it makes that any number (including zero) of the character before is matched. Here are some strings which would be matched by this expression:

Code:

az
aaz
aaaz
aaaaz
...

The one string NOT matched by the expression is this: aa*z, because the asterisk - unlike the "a" - doesn't match itself, only the way other characters (in this case the "a") match something.

In general, if you want to use a metacharacter as normal character you need to [i]escape[/icode] it. To escape it means you put a backslash ("\") in front of it:

Code:

sed -n '/aa\*z/p' /some/file

This changes the "*" to be a normal character and the only string this expression will match now is:

Code:

aa*z

and nothing else. The slash ("/") is also a metacharacter because it is used to mark beginning and end of a regular expression. In the above /aa*z/ it is not encluded in the string we searched for but acts only as a separator, similar to quotes like "this", which don't belong to the word they surround either. And therefore it needs to be escaped the same way as the asterisk:

Code:

sed -n -e '/server01:~ # cat/proc/mdstat/,$p'      # wrong
sed -n -e '/server01:~ # cat\/proc\/mdstat/,$p'                # correct

You need to do this with all metacharacters in your search expression. The most used ones are:

Code:

/
*
[
]
.

Btw., you should NOT use more for this purpose and you do not need to use separate sed calls for this:

Code:

server01:~ # more sample.txt | sed -n -e '/server01:~ # cat/proc/mdstat/,$p' | sed -e '/server01:~ # df -k/,$d'

write it like this instead:

Code:

server01:~ # sed -n -e '/server01:~ # cat/proc/mdstat/,$p' -e '/server01:~ # df -k/,$d' sample.txt

or even like this - ";" is used as separator between consecutive commands:

Code:

server01:~ # sed -n -e '/server01:~ # cat/proc/mdstat/,$p;/server01:~ # df -k/,$d' sample.txt

I hope this helps.

bakunin

Originally Posted by RudiC

I'm sorry I don't understand your request at all.


If you're after a solution to include a slash / in the address, you can
- escape it (\/)
- use another character for the address delimiters. man sed:c