Shell Programming and Scripting

As I stated in a previous thread - I'm a newbie to Unix/Linux and programming. I'm trying to learn the basics on my own using a couple books and the exercises provided inside.

I've reached an exercise that has me stumped. I need to write a bash script that will will read in a file and print the line number and script line of all lines including comments. Normally this wouldn't be difficult, but I'm not supposed to use sed, awk, grep, etc (only Bash). I have the skeleton in place, but I'm missing how to pull only the comments and display the line number. Any help would be appreciated.

Code:

#!bin/bash

while read line
do
echo $line
done

Hello ksmarine1980,

Following may help you in same if we need to print line number along with line's content.

Code:

i- awk '{print NR OFS $0}' Input_file
ii- cat -n Input_file
iii- while read line
    do
    let "i = i + 1"
    echo $i " " $line
    done < "Input_file"

Thanks,
R. Singh

Thank you, Singh! But I'm trying to do this without the use of sed, awk, grep, etc.

Hello ksmarine1980,

Not sure if I am correct, but I have given a while loop solution also in my previous post. Could you please let me know if that helps or you need anything else here.


Thanks,
R. Singh

Thank you Singh! I misread your post. I'll give it a shot, and appreciate your help.

In command arguments have variables in quotes!

Code:

echo "$line"

Code:

echo "$i   $line"

Other suggestions:

Code:

printf "%05d %s\n" $i "$line"

Code:

read -r ...

For the purposes of this exercise, how do you define "comment"?

A basic outline of what you want is something like:

Code:

#!/bin/bash
n=1
while read -r line
do      if [ comment_present ]
        then    printf '%d\t%s\n' $n "$line"
        fi
        n=$((n + 1))
done < file

If you assume that any line containing an octothorpe (#) has a comment, comment_present could be:

Code:

"$line" != "${line#*#}"

but, of course, that will treat quoted and backslash escaped octothorpes as comments when bash would not.

Writing a full parser to find C or shell or some other language's comments accurately in bash is a non-trivial challenge.