Homework & Coursework Questions

Well my last assignment came and i tried some things but i guess it's pretty puzzling for me to figure out all the points of the problem. I was able to achieve something but it's not complete.

1. The problem statement, all variables and given/known data:
Write a bash program which strips the comments from a bash source file:

a) Input the name of the bash source file as a command line argument, or

Input lines of bash source from standard input (your choice).

b) Remove single-line comments beginning with #
(# inside ' ' or inside " " or after \ does not begin a comment)

c) Output the stripped source file to a disk file with the string -strip
inserted between the basename and the extension.
(e.g. input file foo.bash should produce output file foo-strip.bash), or

Output the stripped lines of bash source to standard output (your choice).


It is not necessary to check if the source file is readable or is a valid bash program.


2. Relevant commands, code, scripts, algorithms:

In terms of commands i believe either sed, grep or awk.

3. The attempts at a solution (include all code and scripts):

I was able to create a script that strips the file of comments that at the beginning of a line they start with #. here is the script. However that doesn't fulfill the requirements of the problem.

#This script removes single-line comments begining with #.

Code:

 
if [ $# -eq 0 ]
then
  echo "Usage: $0 needs an argument. "
elif [ $# -eq 1 ]
then
  if [ -d "$1" ]
  then
    echo "\"$1\" is not a file. This is a directory."
  elif [ -f "$1" ]
  then
    cat $1 | grep -v "^#" > $1-strip.bash
    echo Showing the stripped file ... ; sleep 2
    cat $1-strip.bash | less
  fi
fi

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):

diablo valley college, ca, usa, stuart fogg, 171 intro to unix

Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).

use

Code:

grep -v "^[ ^I]*#" $1 > $1-strip.bash          (where ^I represents tab and escape # character if required)

instead of

Code:

cat $1 | grep -v "^#" > $1-strip.bash

I have tried that command but here is what happens. it strips the comment from the line when it starts with # but also if you have a command and then you have # than it will delete the whole line including the command. that's not good for the file.

What this script should do is eliminating comments that are also in the middle of a command keeping the command and cutting the # and whatever is after it.
also should ignore # if it is quoted or escaped like ' ... # ... " " ... # ..." \# ...
he was saying about using a lot of ifs statements for this but i couldn't think of what else to use for the if statements ... like sed or still grep ?

Trick here is to process the file 1 character at a time. Use variables to keep track of being in a single string, double string or comment. Awk probably makes it the easiest

Try something like this

Code:

#!/bin/awk -f
{ for (i=1;i<=length($0);i++) {
  C=substr($0,i,1);
  if (!SQuote && !DQuote && C=="#") Comm=1;
  if (Comm) continue;
  printf C;
  ...  Set SQuote DQoute here to indicate in quotes also handle '\' character ...
  }
  Comm=0;
  printf "\n";
}

Remember that if you're in a double quote string, single quotes don't apply (eg A="It's Fun"), and vica-verca.

Chubler_XL thank you very much for the input.

But i have a question for you ? do you think that this type of problem is for a introduction to UNIX class or is more for an advanced in unix? The reason i am asking is that I would love to be able to make it work using an awk format, but the code that you posted it is too advanced to even understand its logic, for me right now. Again thanks for the effort.

Yes it is too advanced for a intro course. The requirement is probably only lines that begin with comments and ignore strings that span multiple lines and may contain #

You probably just need something like this:

Code:

grep -E "^[[:blank:]]*#" MyBashScript.sh