Multiline delete with sed

Question

I'm trying to use sed to delete all occurrences of

#ifdef _WIN32

#endif

Where all that exists between #ifdef and #endif is an empty line. I have limited experience using sed, I've read some documentation on the multi line features but I can't seem to figure it out. Any help is appreciated!

Does it have to be sed? Would perl be OK? – derobert Jan 05 '11 at 19:02 — derobert, Jan 05 '11 at 19:02

score 5 · Answer 1 · answered Jan 05 '11 at 19:03

5

You can try sed -e '/^#ifdef _WIN32/,/^#endif/d' but it does not generalize to more complex cases of nesting.

answered Jan 05 '11 at 19:03

Ben Jackson

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where i can find the documentation for this /,/ ? – Guilherme Jul 06 '12 at 03:31
@Guilherme you can see it in the manual page where it talks about *addresses*. Any two addresses can be joined by a comma to make an inclusive range. E.g. `1,$` for the whole file, or `/hello/,$` for a line containing `hello` until the end of the file, or `1,10` for the first 10 lines. – Ben Jackson Jul 06 '12 at 05:01

score 4 · Accepted Answer · edited May 23 '17 at 12:14

4

For this job, I'd recommend using a tool designed for the job - rather than sed.

Use coan; it has a mode for editing #ifdef and #ifndef and #if and #elsif lines selectively. For example, you'd use:
```
coan source -U_WIN32 sourcefile.c
```

This would deal with all _WIN32 sections, leaving behind only what was necessary.

See also my related question: Is there a C pre-processor which eliminates #ifdef blocks based on values defined/undefined?

edited May 23 '17 at 12:14

Community

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answered Jan 05 '11 at 22:41

Jonathan Leffler

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Thanks for contributing this one. I knew such a program existed when I gave the `sed` answer but I didn't find it with quick googling. – Ben Jackson Jan 05 '11 at 22:49

SiegeX · Answer 3 · 2011-01-05T19:36:24.627

If there exists pairs of #ifdef _WIN32/#endif that have non-empty lines between them that you don't want to delete, then use the following:

sed 'N;N;s/\n#ifdef _WIN32\n[[:space:]]*\n#endif\n/\n/;P;D'

Input

this is the first line
#ifdef _WIN32
  // Don't delete this comment!
#endif

stuff here
more stuff here
#ifdef _WIN32

#endif
last line

Output

$ sed 'N;N;s/\n#ifdef _WIN32\n[[:space:]]*\n#endif\n/\n/;P;D' ifdef.sed
this is the first line
#ifdef _WIN32
  // Don't delete this comment!
#endif

stuff here
more stuff here
last line

Multiline delete with sed

3 Answers3

Input

Output