Script using awk to find and replace a line, how to ignore comment lines Post: 303039483

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Top Forums Shell Programming and Scripting Script using awk to find and replace a line, how to ignore comment lines Post 303039483 by MadeInGermany on Monday 7th of October 2019 05:05:42 PM

10-07-2019

Registered User

The RE searches require some quoting effort.
The index() function searches for plain strings and returns the position.
Also only the comments left from the search string matter.
Two reasons to go for the index() function rather than the RE.

Code:

# replace multiplier of SHMEMSIZE in sizedefs.h with $num_pages*pagesize
# generated value to substitute for current line
numpages_find_line="#define SHMEMSIZE (4096 "
numpages_replacement_line="#define SHMEMSIZE (4096 * $num_pages)"
# value of comment character for current src file, C code in this case
comment_ch1='//'
comment_ch2='/*'
# path to file we are working on
filename='./src/sizedefs.h'
# process file to switch out line to replace
awk -v find="$numpages_find_line" \
    -v replace="$numpages_replacement_line" \
    -v comment1="$comment_ch1" \
    -v comment2="$comment_ch2" \
    '
    {
      comm1pos=index($0,comment1)
      comm2pos=index($0,comment2)
      commpos=((comm1pos > 0 && comm1pos < comm2pos || comm2pos == 0 ) ? comm1pos : comm2pos)
# commpos := the leftmost comment
      findpos=index($0,find)
# unchanged if commpos is left from findpos or not found
      if (commpos > 0 && commpos < findpos || findpos == 0)
        print $0;
      else
        print replace;
    }
    ' $filename > tmp
mv tmp $filename

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LEARN ABOUT REDHAT

igawk

IGAWK(1)							 Utility Commands							  IGAWK(1)

NAME

       igawk - gawk with include files

SYNOPSIS

       igawk [ all gawk options ] -f program-file [ -- ] file ...
       igawk [ all gawk options ] [ -- ] program-text file ...

DESCRIPTION

       Igawk is a simple shell script that adds the ability to have ``include files'' to gawk(1).

       AWK programs for igawk are the same as for gawk, except that, in addition, you may have lines like

	      @include getopt.awk

       in your program to include the file getopt.awk from either the current directory or one of the other directories in the search path.

OPTIONS

       See gawk(1) for a full description of the AWK language and the options that gawk supports.

EXAMPLES

       cat << EOF > test.awk
       @include getopt.awk

       BEGIN {
	    while (getopt(ARGC, ARGV, "am:q") != -1)
		 ...
       }
       EOF

       igawk -f test.awk

SEE ALSO

       gawk(1)

       Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995.

AUTHOR

       Arnold Robbins (arnold@skeeve.com).

Free Software Foundation					    Nov 3 1999								  IGAWK(1)

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