please explain this sed shell script to remove C++ comments. Post: 302289164

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Top Forums Shell Programming and Scripting please explain this sed shell script to remove C++ comments. Post 302289164 by Priyaranjan on Thursday 19th of February 2009 01:22:09 AM

02-19-2009

Registered User

please explain this sed shell script to remove C++ comments.

#! /bin/sed -nf

# Remove C and C++ comments, by Brian Hiles (brian_hiles@rocketmail.com)

# Sped up (and bugfixed to some extent) by Paolo Bonzini (bonzini@gnu.org)
# Works its way through the line, copying to hold space the text up to the
# first special character (/, ", '). The original version went exactly a
# character at a time, hence the greater speed of this one. But the concept
# and especially the trick of building the line in hold space are entirely
# merit of Brian.

:loop

# This line is sufficient to remove C++ comments!
/^\/\// s,.*,,

/^$/{
x
p
n
b loop
}
/^"/{
:double
/^$/{
x
p
n
/^"/b break
b double
}

H
x
s,\n$.[^\"]*$.*,\1,
x
s,.[^\"]*,,

/^"/b break
/^\\/{
H
x
s,\n$.$.*,\1,
x
s/.//
}
b double
}

/^'/{
:single
/^$/{
x
p
n
/^'/b break
b single
}
H
x
s,\n$.[^\']*$.*,\1,
x
s,.[^\']*,,

/^'/b break
/^\\/{
H
x
s,\n$.$.*,\1,
x
s/.//
}
b single
}

/^\/\*/{
s/.//
:ccom
s,^.[^*]*,,
/^$/ n
/^\*\//{
s/..//
b loop
}
b ccom
}

:break
H
x
s,\n$.[^"'/]*$.*,\1,
x
s/.[^"'/]*//
b loop

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LEARN ABOUT NETBSD

break

break(1)							   User Commands							  break(1)

NAME

       break, continue - shell built-in functions to escape from or advance within a controlling while, for, foreach, or until	loop

SYNOPSIS

   sh
       break [n]

       continue [n]

   csh
       break

       continue

   ksh
       *break [n]

       *continue [n]

DESCRIPTION

   sh
       The break utility exits from the enclosing for or while loop, if any. If n is specified, break n levels.

       The continue utility resumes the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

   csh
       The  break  utility  resumes  execution after the end of the nearest enclosing foreach or while loop. The remaining commands on the current
       line are executed. This allows multilevel breaks to be written as a list of break commands, all on one line.

       The continue utility continues execution of the next iteration of the nearest enclosing while or foreach loop.

   ksh
       The break utility exits from the enclosed for, while, until, or select loop, if any. If n is specified,	then  break  n	levels.  If  n	is
       greater than the number of enclosing loops, the outermost enclosing loop shall be exited.

       The  continue utility resumes the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-
       th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words that follow a command preceded by ** that are in the format of a variable assignment are expanded with the same rules as a  vari-
	   able  assignment.  This means that tilde substitution is performed after the = sign, and also that word splitting and file name genera-
	   tion are not performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), exit(1), ksh(1), sh( 1), attributes(5)

SunOS 5.10							    17 Jul 2002 							  break(1)