CODEWITHSUNDEEP
sed
lyricat
lyricat

Reputation: 1996

Multiline delete with sed

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!

Upvotes: 5

Views: 3403

Answers (3)

Jonathan Leffler
Jonathan Leffler

Reputation: 753665

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?

Upvotes: 4

SiegeX
SiegeX

Reputation: 140307

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

Upvotes: 2

Ben Jackson
Ben Jackson

Reputation: 93710

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

Upvotes: 5

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