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grep backreferencing question

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# 15  
Old 10-19-2010
grep backreferencing question
Quote:
Originally Posted by Scrutinizer
That wasn't part of your problem statement, was it? Anyway,
Code:
grep -E 'int .*([^,]+),.*\1[,\;]|int .*,[,\;]' infile

Code:
grep 'int .*\([^,][^,]*\),.*\1[,\;]\|int .*,[,\;]' infile


To be clear:

int a123,b,c; --- legal
int 12a,b; ---- illegal since the variable starts with a number
int A,b,c ---- illegal since the variable starts with [A-Z]


A few valid lines that should match (only when a variable occurs more than once):

int a,b,a;
int a,b,b;
int a,b,c,a,g;

---------- Post updated at 03:12 PM ---------- Previous update was at 03:07 PM ----------
Quote:
Originally Posted by DGPickett
Wrong comes in so many flavors, like integral calculus. Even right has a lot of flavors. First there are the datatypes, then the commas, the initializations, typedefs, unions, structs, Classes, code, continued lines, includes, macros.

Why not cc -c ? I hope it knows enough to catch that. There may even be c verification tools out there. Ever try lint?

Oh.. But it matches something like:

int aa; --- which should not match.
# 16  
Old 10-19-2010
@DGPickett, The \< , \> are GNU-only, no?
# 17  
Old 10-19-2010
If we have \(a\(b\)\)

Which is \1, which is \2?
# 18  
Old 10-19-2010
First opened is first numbered, but try it and see.

sed 's/\(\(.\).\).*/\1 \2/' <<!
abcdefg
!
ab a
This User Gave Thanks to DGPickett For This Post:
prasanna1157
# 19  
Old 10-19-2010
Yes, first is \1.

Thanks.
# 20  
Old 10-19-2010
Quote:
Originally Posted by Corona688

There's definitely backreferencing in egrep.
According to the Posix Specification there is no back reference in ERE, while there is back reference in BRE. compare:
9.3.6 BREs Matching Multiple Characters
9.4.6 EREs Matching Multiple Characters
# 21  
Old 10-19-2010
That statement may be true, but is worthless out of school. Smilie
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