How to remove comments from a bash script?


 
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# 8  
Old 06-22-2012
I find it sufficient to strip lines which consist totally of comments or white space when examining a script. This is only for visual inspection because it can still remove significant lines from Here Documents.

Stripping comments on a permanent basis is not advisible at all and could breach copyright in commercial code.
# 9  
Old 06-22-2012
Question

My main purpose for the post #1 is to compare two copies (or two versions) of the script, ignoring comments and meaningless white spaces that do not affect execution.

If commands like diff or cmp provide an option to ignore comments and meaningless white spaces, and if two copies (or two versions) of the script can be compared without permanently removing comments and meaningless white spaces, I would be partially satisfied. Does anyone know how to compare two copies (or two versions) of bash script, ignoring comments and meaningless white spaces? I would appreciate it if you show me such a technique.

Even if diff or cmp has an option to ignore comments and meaningless white spaces, the permanent removal of comments and meaningless white spaces would be useful in the following situation. If they are permanently removed, I would be able to take the resultant copies to a GUI OS. I feel more comfortable to perform the comparison on a graphical environment on a GUI OS, after performing the removal on a text-based Unix machine.
# 10  
Old 06-22-2012
Quote:
Originally Posted by LessNux
My main purpose for the post #1 is to compare two copies (or two versions) of the script, ignoring comments and meaningless white spaces that do not affect execution.
Again, a program that can tell the difference between comments and meaningful code in a shell script, is probably a shell...
# 11  
Old 07-04-2012
I recently got to know that, if a hash mark (#) to begin a shell comment is not placed at the beginning of a line, then the hash mark must be preceded by a horizontal whitespace. (The # mark is also called a "pound sign" in the United States, and a "number sign" as a Unicode name.)

I have never seen any Unix guide documents explicitly state the need for a space before a hash mark (#) to begin a comment. C++ allows comment-leading double slashes (//) to immediately follow another token without any spaces preceding the double slashes. So, I thought that BASH would not require any spaces before a hash mark (#) that begins a comment.

I recently read carefully a man page of bash, which writes, "a word beginning with # causes that word and all remaining characters on that line to be ignored." The phrase "a word beginning with #" obscurely implies that a space is required before # if the comment-leading # is not placed at the beginning of a line.


Now, let me go back to my initial problem. I need to compare two copies of a bash script. One copy is full of detailed comments. The other copy has few or no comments. The two copies differ also in spacing. In terms of command statements that affect execution, the two copies are almost identical. So, I would like to remove comments before comparing the two copies. The following script now gives me most of what I wanted. I named the script "rmcomment.sh".

Code:
#!/bin/bash

# SYNOPSIS
# rmcomment.sh INFILE OUTFILE
#
# DESCRIPTION
# This script performs the following:
#
# - removes comments
# - removes all the horizontal whitespaces at the end of line
# - removes lines that consist of only horizontal whitespaces
# - removes blank lines
# - reduces consecutive multiple horizontal whitespaces into one space.
#
# CAVEAT
# While bash does not consider a quote-escaped hash mark to be
# a comment starter, this code is not smart enough to take
# quotes into account.  Thus, this code removes the
# quote-escaped hash mark and all the characters after it on
# the line, if the quote-escaped hash mark is preceded by a
# horizontal whitespace.
#



perl -pe 's/(^|[[:blank:]]+)#.*$//g ; s/[[:blank:]]+$//g' $1 | \
grep -v ^[[:space:]]*$ | perl -pe 's/[[:blank:]][[:blank:]]+/ /g' > $2


Here is a sample input.

Code:
# line01 comment1  
line02 # comment2  
line03# word3  
line04 followed by spaces  
    

line07     hello    world
line08 'abcd#efgh'
line09 "abcd#efgh"
line10 'abcd #efgh'
line11 "abcd #efgh"
Note: Lines 1-4 end with spaces.
Note: Line 5 consists of only spaces.
Note: Line 6 is a blank line.

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