Shell Programming and Scripting

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.

Can you please post your script, or some lines of you script?

@arrals_vl
It's the Perl program at the beginning of Post #1 .

Code:

egrep -i -v "^#|^$" file

?

I mean the script where you want to remove the comments...not the script that removes the comments.

The problem is, to understand which # are comments and which # aren't, you have to understand the script. "#" '#' should not be stripped out for instance -- or any other time # is not given to the bare line but wrapped inside something. It's possible to wrap # inside quite complex structures, I'm not sure you can check for every possible thing with regexes alone.

What's the best thing out there for understanding scripts? A shell, of course.

There is an option for the shell to print lines as it executes them(which strips out comments). Also, an option to check lines for syntax without actually running them. Unfortunately they seem to be mutually exclusive. Seeing if there's anything else relevant...

I'm curious. Why?

Regards,
Alister

---------- Post updated at 12:21 PM ---------- Previous update was at 12:11 PM ----------

Also, while your post makes it clear that you are aware that naively removing #.* can cause problems, the same is true for a blank line. If it is part of a heredoc or some other quoted string, removing a blank line alters the meaning of the script.

Regards,
Alister