UNIX for Dummies Questions & Answers

I suspect this is commonly done, but haven't found the right combination of search terms to find the answer.

I want to grep for lines in .cpp files that contain only 1 '=' sign in an if statement. e.g.,
if (a = b) -- find this
if (a==b) -- don't find this

My attempt:

Code:

egrep "^if\b*\(.+=[^=]*" *.cpp

This finds lines with 1 =, but it is also finding lines with ==.

Also, if i use grep instead of egrep I get "RE error 42: \( \) imbalance".

Code:

$ cat file
if (a = b) -- find this
if (a==b) -- don't find this
$ grep "if.*[^=]=[^=]" file
if (a = b) -- find this

Code:

ant:/home/vbe $ cat file
a=b
a==b
a=c
c=a
b = c
c == a
ant:/home/vbe $ cat file|grep =|grep -v "=="
a=b
a=c
c=a
b = c

Anbu23,
Thanks, but this finds != in if statements and lines with variable names that have 'if' in them.

---------- Post updated at 11:50 AM ---------- Previous update was at 11:35 AM ----------

Vbe,

May end up with 2 responses to you - i tried editing response to Anbu23 to add response to you, but it doesn't look like it took. At that time I hadn't found the combination that worked, but this does. Thanks for your response.

cat *.cpp | egrep "^if\b*\(.+=[^=]*" | egrep -v "=="

Part of the exercise was to understand regular expressions. I am still interested in why my expression wasn't eliminating the 2nd = if someone can figure that out. Also, I am still getting the unbalanced expression if I use grep. Any idea why that is?

using anbu23 syntax:

Code:

grep "[^=]=[^=]" file

should work

Regex:

Code:

if\s*\(\w+\s?=\s?\w+\)

vbe,

I tried Anbu23's syntax by itself and it found too many non-matching lines. I tried it combined with what I had (adding in the [^=] before =)

Code:

egrep "^if\b*\(.+[^=]=[^=]*" *.cpp

but it still found the same lines it finds without his addition - i.e., ones with ==.
However, if I take away the final *, then it DOES work, which makes sense. I see why the final * makes it not work. And now I see why the first [^=] is required, so thank you both.

Neo,
Thank you for your suggestion - it is not matching any lines - but it will be helpful as a learning experience trying to tweak it.