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Full Discussion: How to remove comments from a bash script?
Top Forums Shell Programming and Scripting How to remove comments from a bash script? Post 302660261 by LessNux on Friday 22nd of June 2012 09:21:20 AM
Old 06-22-2012
Question How to remove comments from a bash script?
I would like to remove comments from a bash script. In addition, I would like to remove lines that consist of only white spaces, and to remove blank lines.

Code:
#!/bin/bash
perl -pe 's/ *#.*$//g' $1 | grep -v ^[[:space:]]*$ | perl -pe 's/  +/ /g' > $2
#
# $1 INFILE
# $2 OUTFILE


The above code seemed to work at first. Unfortunately, however, I found later that the above code destroys the following two special variables.

${#ARRAY[@]} the number of array elements
$# the number of shell arguments

A workaround is to replace "${#" and "$#" with words that do not appear in the input file before applying the above code.


Code:
sed 's/${#/__UNUSUALWORD1__/g ; s/$#/__UNUSUALWORD2__/g' in.txt | \
perl -pe 's/ *#.*$//g' | grep -v ^[[:space:]]*$ | perl -pe 's/  +/ /g' | \
sed 's/__UNUSUALWORD1__/${#/ ; s/__UNUSUALWORD2__/$#/' > out.txt


However, the preparatory replacement is awkward. I would like to modify 's/ *#.*$//g' so that it will not match "${#" or "$#". Does anyone know a better solution?

Bash comments always start with #. However, the problem is that bash allows some exceptions where # does not lead a comment, as shown below.

Code:
${#ARRAY[@]} the number of array elements
$# the number of shell arguments
\# escaped by a backslash.
'abcd#efgh' protected by quotes
"abcd#efgh" protected by quotes

Does anyone know how to remove comments from bash scripts without destroying the exempted #'s that do not lead comments? (In addition, I would like to remove lines that consist of only white spaces, and to remove blank lines.)

Many thanks in advance.
Last edited by methyl; 06-22-2012 at 11:33 AM.. Reason: more code tags
 

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LEARN ABOUT BSD

unifdef

UNIFDEF(1)						      General Commands Manual							UNIFDEF(1)

NAME

       unifdef - remove ifdef'ed lines

SYNOPSIS

       unifdef [ -t -l -c -Dsym -Usym -idsym -iusym ] ...  [ file ]

DESCRIPTION

       Unifdef	is  useful for removing ifdef'ed lines from a file while otherwise leaving the file alone.  Unifdef is like a stripped-down C pre-
       processor: it is smart enough to deal with the nested ifdefs, comments, single and double quotes of C syntax so that it can do its job, but
       it  doesn't  do any including or interpretation of macros.  Neither does it strip out comments, though it recognizes and ignores them.  You
       specify which symbols you want defined -Dsym or undefined -Usym and the lines inside those ifdefs will be copied to the output  or  removed
       as  appropriate.   The  ifdef,  ifndef, else, and endif lines associated with sym will also be removed.	Ifdefs involving symbols you don't
       specify are untouched and copied out along with their associated ifdef, else, and endif lines.  If an ifdef X occurs nested inside  another
       ifdef X, then the inside ifdef is treated as if it were an unrecognized symbol.	If the same symbol appears in more than one argument, only
       the first occurrence is significant.

       The -l option causes unifdef to replace removed lines with blank lines instead of deleting them.

       If you use ifdefs to delimit non-C lines, such as comments or code which is under construction, then you must tell  unifdef  which  symbols
       are  used  for  that  purpose so that it won't try to parse for quotes and comments in those ifdef'ed lines.  You specify that you want the
       lines inside certain ifdefs to be ignored but copied out with -idsym and -iusym similar to -Dsym and -Usym above.

       If you want to use unifdef for plain text (not C code), use the -t option.  This makes unifdef refrain from attempting  to  recognize  com-
       ments and single and double quotes.

       Unifdef copies its output to stdout and will take its input from stdin if no file argument is given.  If the -c argument is specified, then
       the operation of unifdef is complemented, i.e. the lines that would have been removed or blanked are retained and vice versa.

SEE ALSO

       diff(1)

DIAGNOSTICS

       Premature EOF, inappropriate else or endif.

       Exit status is 0 if output is exact copy of input, 1 if not, 2 if trouble.

BUGS

       Does not know how to deal with cpp consructs such as

	    #if  defined(X) || defined(Y)

AUTHOR

       Dave Yost

4.3 Berkeley Distribution					  April 29, 1985							UNIFDEF(1)
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