Shell Programming and Scripting

Hi guys,
I have the following expression :

Code:

typeset EXBYTEC_CHK=`egrep ^"[^0-9]+${PNUM}[^0-9]" /bb/data/firmexbytes.dta`

can anybody please explain to me what

Code:

^"[^0-9]+${PNUM}[^0-9]"

stands for in egrep statement? Thanks -A

I am going to try to...
the first "^" means that the pattern should match from the beginning.
the [ means match any of the character till ]
in your case the immediate first character after [ is ^, which has a special meaning i.e. match anything other than the next character.
Now it happens that your next character 0-9 is not one character but a range (because of the -)
So that [^0-9] means is match anything other than the characters 0 through 9.
the next character in your pattern is '+' which means one or more of these.
So to recap till here... ^"[^0-9]+ means match from the beginning any characters that are not 0 though 9.
Next I am not sure what ${PNUM} is. Sorry cant explain that.
and then [^0-9] again means the same as above.

I wish I could better explain with examples.
Ok, lemme try that too...
So your pattern is going to match abcd${PNUM}a but it is not going to match ab23${PNUM}a not abcd${PNUM}2.

I hope that makes sense.

egrep ^"[^0-9]+${PNUM}[^0-9]" /bb/data/firmexbytes.dta

First - ${PNUM} is just a variable that contains a string - any string.

So now, let's break down the egrep command chunk by chunk...

egrep ^
This means start looking for the pattern at the start of each line

egrep ^"[^0-9]+
The ^ inside the bracket before a pattern means NOT. 0-9 mean any digit 0 thru 9. So [^0-9] means look for any single character that is not a digit 0 thru 9. The + means match 1 or more instance of the preceding expression. So ^"[^0-9]+ means look for 1 or more characters in a row that are not digits 0 thru 9 starting at the beginning of each line.

egrep ^"[^0-9]+${PNUM}
${PNUM} is just a variable that contains a string - any string. So ^"[^0-9]+${PNUM} means look for the string ${PNUM} and return the line as long as there are no numbers preceding the string ${PNUM}.

egrep ^"[^0-9]+${PNUM}[^0-9]"
Finally we end with [^0-9] which says look for any single character that is not a digit 0 thru 9. And since there is no + after it, it says to only look at the next character after ${PNUM} is found. And it MUST find at least one non-numeric character.


For the sake of this discussion let's say that:

PNUM=junk

So - the egrep statement will scan the /bb/data/firmexbytes.dta file and return any lines that have the string "junk" in it with 1 or more characters before the string with none of them a number AND a character that exists immediately after "junk" that is not a number.

Here's another example:

PNUM=1234

In this case - the egrep statement will scan the /bb/data/firmexbytes.dta file and return any lines that have the string "1234" in it with 1 or more characters before the string with that are not a number AND a character that exists immediately after "1234" that is not a number.


Want to have fun? Put the following in a file called file1:

Code:

junk
ajunk
0junk
ajunk0
ajunka
abcjunkz
abcjunkxyz
abcjunkx12
a0cjunka
junka
junk0

Then run

Code:

PNUM=junk
egrep ^"[^0-9]+${PNUM}[^0-9]" file1

Of all those values found in the list above, egrep will only return these:
ajunka
abcjunkz
abcjunkxyz
abcjunkx12
because they are the only ones that have the string "junk" in it with 1 or more characters before the string with none of them a number AND a character that exists immediately after "junk" that is not a number.

abcjunkx12 should not be a surprise ...

Now change junk to 1234 both in the file and as the value of PNUM and try the egrep again.

Got it??? Should be clear as mud at this point....

Thanks a lot guys for your time and explanations