Bash Challenge

amboxer21 · 01-24-2015, 09:23 PM

Here is a program I had to write for work that I really enjoyed writing. I figured I would see if anyone else would like to try.

RULES: There are no rules. Just make it as clean as possible.

GUIDELINES: You are given a file with 4 wireless interfaces. You must monitor both of the overruns values for it's respective iface and check if the values are incrementing. For each time you check and the value is indeed incrementing for either overrun, you need to keep track. Once the counter value for its respective iface reaches 5, restart the iface. Also, the files must be hidden so it looks clean.

TEST FILE:

Code:

eth0      Link encap:Ethernet  HWaddr 78:24:af:6e:a6:60  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:337 errors:0 dropped:0 overruns:0 frame:0
          TX packets:337 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:25551 (25.5 KB)  TX bytes:25551 (25.5 KB)

wlan0     Link encap:Ethernet  HWaddr 68:a3:c4:85:24:b4  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:21 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

eth1      Link encap:Ethernet  HWaddr 78:24:af:6e:a6:60
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:337 errors:0 dropped:0 overruns:0 frame:0
          TX packets:337 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:25551 (25.5 KB)  TX bytes:25551 (25.5 KB)

wlan1     Link encap:Ethernet  HWaddr 68:a3:c4:85:24:b4
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:10 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

eth2      Link encap:Ethernet  HWaddr 78:24:af:6e:a6:60
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:337 errors:0 dropped:0 overruns:0 frame:0
          TX packets:337 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:25551 (25.5 KB)  TX bytes:25551 (25.5 KB)

wlan2     Link encap:Ethernet  HWaddr 68:a3:c4:85:24:b4
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:10 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

eth3      Link encap:Ethernet  HWaddr 78:24:af:6e:a6:60
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:337 errors:0 dropped:0 overruns:0 frame:0
          TX packets:337 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:25551 (25.5 KB)  TX bytes:25551 (25.5 KB)

wlan3     Link encap:Ethernet  HWaddr 68:a3:c4:85:24:b4
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

MY SOLUTION:

Code:

#!/bin/bash
#
# Grabs each iface and its respective overruns variables, ties them all together
# and pushes them into the res variable. Resulting in a line for every iface.
res=$(readarray -t mon < <(cat ifconfig | \
	awk '/w[a-z]*[0-9]/,/TX.*overruns:[0-9]/{print}'); echo "${mon[@]}" | \
	egrep -o "(w[a-z]*[0-9]|overruns:[0-9]{1,99})" | \
	sed -e 'N;N;s/\n/ /g');

readarray -t fin < <(echo "$res");

counter=0
for i in "${fin[@]}"; do

# Joins both overrun numbers from same iface together and pushes them into the don variable.
# Each iface has 2 overruns counters. One for TX and one for RX.
don=$(echo "$i" | egrep -o ":[0-9]{1,99}" | sed ':a;N;$!ba;s/\n//g;s/://g');

# Grabs just the iface name and stores it in the if variable.
iface=`echo "$i" | grep -o "w[a-z]*[0-9]\{1,99\}"`;

	# Cretes necessary files if they're not present.
	if [[ ! -f ".${iface}" || ! -f ".${iface}counter" ]]; then
		echo -e "File does not exit. Creating now.\n";
    		touch .${iface};
    		touch .${iface}counter;
  	fi

	# Checks to see if the overruns are greater than zero for each iface in the iteration.
	if [[ $don == '00' ]]; then
		echo -e "$iface remains clean\n";

	else
		echo -e "!!!!! $iface is not clean.\n";
		echo $don >> ".${iface}"; # Pushes the current overrun numbers into a file.

          # Checks if the last line in the respective iface file is greater than the second
          # to last. If that's the case, then it will increment the counter inside that ifaces file.
      		if [[ `cat .${iface} | sed -n '$p'` > `cat .${iface} | sed -n 'x;$p'` ]]; then
        		echo -e "$iface has an incrementing overrun.\n";
        		echo $((`cat .${iface}counter`+1)) > .${iface}counter;

                        # If counter is equal to 5, then reset the respective server.
        		if [[ `cat .${iface}counter` -eq 5 ]]; then
        			echo -e "Restarting Server - ${iface}.\n";
                                echo > .${iface}; # Reset the file and counter after the server has been reset.
                                echo > .${iface}counter
        		fi

		else
			echo -e "Incrementing overruns on $iface has stopped.\n";
		fi
	fi
done

j_v · 01-25-2015, 05:53 PM

This doesn't throw an error? Naming a variable the same as a reserved word (if) seems like it should be a syntax error.

unSpawn · 01-25-2015, 05:57 PM

0) The kernel exposes counters via /proc and, amongst other tools, netstat relies on those. So in /proc/net/dev you have your device name in ARRAY[0] and (IIRC ARRAY[4] and ARRAY[14]) for RX drops and TX drops respectively. Point is you don't need to rely on external binaries like 'netstat' or 'ifconfig', you can read that file as unprivileged user and there's no need to massage the hell out of data using awk / egrep / sed. 1) Biggest no no IMHO is not defining a directory for dumping in data first, now it just ends up in $PWD which can (but shouldn't) be anywhere. 2) Personally I like uppercase variable names as it makes reading easier and I'd use sqlite for storing / querying data but that's prolly just me.

mina86 · 01-26-2015, 12:18 PM

Quote:

Originally Posted by unSpawn

2) Personally I like uppercase variable names as it makes reading easier and I'd use sqlite for storing / querying data but that's prolly just me.

I use upper-case for exported environment variable while lower-case for variables local to the script.

Anyway, back to OP’s post:
3) Use $(…) instead of backticks.

Code:

cat ifconfig |

Code:

cat .${iface} |

Useless Use of Cat™

Code:

sed -n '$p'

That’s IMO better written as ‘tail -n1’.

Code:

echo $((`cat .${iface}counter`+1)) > .${iface}counter

Is that even defined? In any event, the following is much safer:

Code:

counter=$(cat ".${iface}counter")
echo $(( $counter + 1)) >.${iface}counter

Code:

if [[ `cat .${iface}counter` -eq 5 ]]; then

You’ve read that file already? Why not re-use the value? This will also prevent overwriting the counter file twice.

Code:

echo $don >> ".${iface}"; # Pushes the current overrun numbers into a file.

So here’s a thing: You are interested only in current values (stored in ‘$don’) and previous ones (stored in the file). There’s really no need to keep [i]all[/ir of the values in the file. Consider:

Code:

prev=$(cat ".${iface}")
if [ "$don" != "$prev" ]; then
    echo "$don" >."${iface}"
    counter=$(cat ".${face}counter")
    if [ $counter -eq 4 ]; then
        echo -e "Restarting Server - ${iface}.\n";
        echo >.${iface}
        echo >.${iface}counter
    else
        echo $(($counter + 1)) >.${iface}counter
    fi
fi

In fact, I’d keep a single file:

Code:

if ! read prev counter <.${iface}; then
    echo "$don 0" >.${iface}
elif [ "$don" != "$prev" ]; then
    if [ $counter -eq 4 ]; then
        echo -e "Restarting Server - ${iface}.\n";
        : >.${iface}
    else
        echo "$don $(( $counter + 1))" >.${iface}
    fi
fi

Personally though, I would transform ifconfig output into something along the lines of:

Code:

<if-name> <rx-overruns> <tx-overruns> 0

and then using ‘join’ merge output from previous and current run into:

Code:

<if-name> <prev-rx-overruns> <prev-tx-overruns> <prev-counter> <rx-overruns> <tx-overruns> 0

This can be easily processed line-by-line.

UPDATE: Of course by ‘I would’ I mean ‘if I had to use ifconfig, I would’. In reality, /proc is your friend.

grail · 01-27-2015, 10:02 AM

I am curious how the following line works?

Code:

cat ifconfig

Is there some form of redirection at work here I am not aware of??

Also the following line:

Code:

echo $((`cat .${iface}counter`+1)) > .${iface}counter;

From what I can see '.${iface}counter' file contains overrun numbers stored in 'don' variable. After placing all the awk/sed/grep/cat's together, I see for wlan0 the first entry would be 210.
Whilst I am not sure how this is a valid value or number, when I run the left side of the redirect I get the following error:

Code:

echo $((`cat .wlan0counter` + 1))
211

Now assuming it did return output plus 1, I still fail to see how '211' is a useful figure??

I am not understanding how we are getting the 5 rounds here?

amboxer21 · 01-27-2015, 10:22 AM

[QUOTE=mina86;5306972]I use upper-case for exported environment variable while lower-case for variables local to the script.[\QUOTE]

Agreed. I do the same.

Quote:

Originally Posted by mina86

Anyway, back to OP’s post:
3) Use $(…) instead of backticks.

Is there a specific reason? They behave the same. The only difference is syntactical. It is easier to nest $() than it is to nest ``.

Quote:

Originally Posted by mina86

Code:

cat ifconfig |

Code:

cat .${iface} |

Useless Use of Cat™

It really isn't. If you think I wrote all of this without knowing that I cannot use cat in conjunction with a command like ifconfig, you my friend are either oblivious or ignorant. It's obviously a file. Take a look at my OP and you will see the words test file in bold. It includes output from the ifconfig command. I guess I wouldn't notice the error my script wold throw if this weren't the case.

Quote:

Originally Posted by mina86

Code:

sed -n '$p'

That’s IMO better written as ‘tail -n1’.

It's a matter of choice. There is no real difference here. Only your opinion. Thank you though.

Quote:

Originally Posted by mina86

Code:

echo $((`cat .${iface}counter`+1)) > .${iface}counter

Is that even defined? In any event, the following is much safer:

Code:

counter=$(cat ".${iface}counter")
echo $(( $counter + 1)) >.${iface}counter

Much safer? In what way? Please explain. In my approach, I am taking the output of my counter file for it's respective iface and overwriting the old counter number in one pass.

Quote:

Originally Posted by mina86

Code:

if [[ `cat .${iface}counter` -eq 5 ]]; then

You’ve read that file already? Why not re-use the value? This will also prevent overwriting the counter file twice.

Separate functions. One increments and one checks to see if the counter has reached 5. I'm not overwritting the file twice. Only once. I guess I could combine the 2 functions in an if loop.

Quote:

Originally Posted by mina86

Code:

echo $don >> ".${iface}"; # Pushes the current overrun numbers into a file.

So here’s a thing: You are interested only in current values (stored in ‘$don’) and previous ones (stored in the file). There’s really no need to keep [i]all[/ir of the values in the file. Consider:

Code:

prev=$(cat ".${iface}")
if [ "$don" != "$prev" ]; then
    echo "$don" >."${iface}"
    counter=$(cat ".${face}counter")
    if [ $counter -eq 4 ]; then
        echo -e "Restarting Server - ${iface}.\n";
        echo >.${iface}
        echo >.${iface}counter
    else
        echo $(($counter + 1)) >.${iface}counter
    fi
fi

In fact, I’d keep a single file:

Code:

if ! read prev counter <.${iface}; then
    echo "$don 0" >.${iface}
elif [ "$don" != "$prev" ]; then
    if [ $counter -eq 4 ]; then
        echo -e "Restarting Server - ${iface}.\n";
        : >.${iface}
    else
        echo "$don $(( $counter + 1))" >.${iface}
    fi
fi

Personally though, I would transform ifconfig output into something along the lines of:

Code:

<if-name> <rx-overruns> <tx-overruns> 0

and then using ‘join’ merge output from previous and current run into:

Code:

<if-name> <prev-rx-overruns> <prev-tx-overruns> <prev-counter> <rx-overruns> <tx-overruns> 0

This can be easily processed line-by-line.

UPDATE: Of course by ‘I would’ I mean ‘if I had to use ifconfig, I would’. In reality, /proc is your friend.

Personally, I think you should not be such a jerk! If you're going to try and rip my code apart, at least be constructive. Explain yourself or give me some tips. Not sure if I am being sensitive but I am a bit offended. I don't believe I am because I wasn't offended when unspawn replied with "constructive" criticism.

amboxer21 · 01-27-2015, 10:29 AM

Quote:

Originally Posted by grail

I am curious how the following line works?

Code:

cat ifconfig

Is there some form of redirection at work here I am not aware of??

Also the following line:

Code:

echo $((`cat .${iface}counter`+1)) > .${iface}counter;

From what I can see '.${iface}counter' file contains overrun numbers stored in 'don' variable. After placing all the awk/sed/grep/cat's together, I see for wlan0 the first entry would be 210.
Whilst I am not sure how this is a valid value or number, when I run the left side of the redirect I get the following error:

Code:

echo $((`cat .wlan0counter` + 1))
211

Now assuming it did return output plus 1, I still fail to see how '211' is a useful figure??

I am not understanding how we are getting the 5 rounds here?

Sorry that command is actually a file.

The parsing takes the overruns for it's respective iface and pushes it into a file. If the overruns for the given iface were 0 for both rx and tx, then the result would be 00. If either or were to increment, it would still be incremented with 01 or 10. It grabs the over runs and pushes them into its respective file and compares the last 2 lines and checks if the last value is greater than the previous value. Then acts accordingly.

NevemTeve · 01-27-2015, 10:45 AM

Off: Imho the problem with shell scripts is that they are easy to write but hard to understand/debug/maintain/reuse. Also they are slow and prone to be platform-dependent. That's why I suggest writing programs in some actual programming language (script or otherwise).

mina86 · 01-27-2015, 11:56 AM

Quote:

Originally Posted by amboxer21

Is there a specific reason? They behave the same. The only difference is syntactical. It is easier to nest $() than it is to nest ``.

Isn’t that reason enough? $(…) is easier to use than backticks so why not use it? [UPDATE: At unSpawn’s request, here’s a whole article about it: Why is $(...) preferred over `...` (backticks)?]

Quote:

Originally Posted by amboxer21

It really isn't.

cat ifconfig | … is equivalent to <ifconfig … and cat .${iface} | … is equivalent to <.$iface … so yes, it is a Useless Use of Cat™.

Quote:

Originally Posted by amboxer21

Much safer? In what way? Please explain. In my approach, I am taking the output of my counter file for it's respective iface and overwriting the old counter number in one pass.

You are relying on the fact that $((`cat .${iface}counter`+1)) will be fully evaluated prior to >.${iface}counter. Maybe ‘much safer’ is exaggeration but your approach to me looks at least suspicious.

Quote:

Originally Posted by amboxer21

Separate functions. One increments and one checks to see if the counter has reached 5. I'm not overwritting the file twice. Only once. I guess I could combine the 2 functions in an if loop.

If counter reaches five, you first execute echo $don >> ".${iface}"; (which is always run) and then echo "$don" >."${iface}" (which zeroes the data once limit is reached). You can simply move appending $don to the file, i.e.:

Code:

		echo -e "!!!!! $iface is not clean.\n";

		# Checks if the last line in the respective iface file is
		# greater than the second to last. If that's the case, then it
		# will increment the counter inside that ifaces file.
		if [ "$don" != "$(tail -n1 <.${iface})" ]; then
			echo -e "$iface has an incrementing overrun.\n";
			echo $((`cat .${iface}counter`+1)) > .${iface}counter;

			# If counter is equal to 5, then reset the respective
			# server.
			if [[ `cat .${iface}counter` -eq 5 ]]; then
				echo -e "Restarting Server - ${iface}.\n";
				# Reset the file and counter after the server
				# has been reset.
				echo > .${iface}
				echo > .${iface}counter
			else
				# Pushes the current overrun numbers into
				# a file.
				echo $don >> ".${iface}"
			fi
		else
			echo -e "Incrementing overruns on $iface has stopped.\n"
		fi

to save on some I/O and simplify the condition in the first if. The next obvious step is to stop appending to the file, since the history of the overrun values is irrelevant:

Code:

		echo -e "!!!!! $iface is not clean.\n";

		# Checks if the last line in the respective iface file is
		# greater than the second to last. If that's the case, then it
		# will increment the counter inside that ifaces file.
		if [ "$don" != "$(cat ".${iface")" ]; then
			echo -e "$iface has an incrementing overrun.\n";
			echo $((`cat .${iface}counter`+1)) > .${iface}counter;

			# If counter is equal to 5, then reset the respective
			# server.
			if [[ `cat .${iface}counter` -eq 5 ]]; then
				echo -e "Restarting Server - ${iface}.\n";
				# Reset the file and counter after the server
				# has been reset.
				echo > .${iface}
				echo > .${iface}counter
			else
				# Pushes the current overrun numbers into
				# a file.
				echo "$don" >.${iface}
			fi
		else
			echo -e "Incrementing overruns on $iface has stopped.\n"
		fi

Quote:

Originally Posted by amboxer21

If you're going to try and rip my code apart, at least be constructive.

I gave you code samples of what I believe would be better solution, I don’t know how to be more constructive then that.

-- UPDATE --
Solution with join:

Code:

#!/bin/sh

file=/tmp/watch-for-overruns
lock=/tmp/watch-for-overruns.lock


set -eu

# Are we the only ones?
exec 9>$lock
flock -n 9 || exit 1

# Make sure we have a file to read from, /dev/null will do if $file
# does not exist
in_file=$file
[ -f "$in_file" ] || in_file=/dev/null

temp=$(mktemp "$file.temp.XXXXXXXXXX")
trap 'rm -f -- "$temp"' 0

# gawk produces lines of the following form:
#     <interface-name> <rx-overruns> <tx-overruns>
<ifconfig gawk -e '
	$0 ~ /^[^ ]/ {
		if (iface ~ /^wlan/) print iface, cnt["RX"], cnt["TX"]
		iface = $1
		cnt["RX"] = cnt["TX"] = 0
	}
	match($0, /^ *[TR]X .*overruns:([0-9]+)/, arr) {
		cnt[$1] = arr[1]
	}
	END {
		if (iface ~ /^wlan/) print iface, cnt["RX"], cnt["TX"]
	}
' | sort | join -a 1 -- - "$in_file" | while read iface rx tx prx ptx cnt; do
	# For lines successfully joined (an old interface), we get:
	#     <if-name> <rx> <tx> <previous-rx> <previous-tx> <counter>
	# For lines that were only in output of gawk (new interface), we get:
	#     <if-name> <rx> <tx>
	# We ignore lines that were in $in_file only (disappearing interface)
	if [ -z "$prx" ]; then
		echo "$iface $rx $tx 0"
	elif [ "$rx" -le "$prx" ] || [ "$tx" -le "$ptx" ]; then
		echo "$iface $rx $tx $cnt"
	elif [ "$cnt" -eq 4 ]; then
		echo "!!! restart $iface" >&2
	else
		echo "$iface $rx $tx $(($cnt + 1))"
	fi
done >$temp

mv -f -- "$temp" "$file"

One thing I don’t like about it is that it uses gawk, but if that’s a problem, it can be fairly simply fixed by first treating output of ifconfig with sed.

UPDATE: Renamed ‘read’ variable to ‘in_file’ as per grail’s suggestion.

unSpawn · 01-27-2015, 12:16 PM

Quote:

Originally Posted by mina86

Isn’t that reason enough? $(…) is easier to use than backticks so why not use it?

Please try to use qualitative arguments and refer to the Bash Hackers Wiki or Gregs Bash Pitfalls or the Advanced Bash-Scripting Guide where you can (or can't).

grail · 01-28-2015, 09:41 AM

Well it makes more sense now at least that 'ifconfig' is a file. May I suggest in future it might be nice to not call variables and files by well known command names to keep it clearer

For me this would extend mina86's code as well where he uses 'read' for a variable name ... I just think these types of things can make the code a little unclear at first glance (just my opinion of course)

I think mina86 has shown a good way forward, but thought I might just throw in a little bash solution for storing the data from your file or in fact a command:

Code:

w_regex='^(wlan[0-9]+)'
o_regex='overruns:([0-9]+)'

# Put our file / command data in an array for easy access
while read -r line
do
  if [[ "$line" =~ $w_regex ]]
  then
    ifaces+=( ${BASH_REMATCH[1]} )
  elif (( ${#ifaces[@]} > 0 )) && \
       [[ "${ifaces[${#ifaces[@]}-${#ifaces[@]}%3]}" =~ wlan && \
          "$line" =~ $o_regex ]]  
  then
    ifaces+=( ${BASH_REMATCH[1]} )
  fi  
done<file_name # or you could go with <(command)

It's not rocket science but just a nice little bash alternative to the grep/sed/awk scenario

rtmistler · 01-28-2015, 12:35 PM

Having some lengthy experience with seeing others, such as grail, unSpawn, and Mina86 as well as others offer BASH improvements, I'd say they are imminently more qualified than I.

I do agree with their comments both about organization, use of resources and names and style. For instance I would use variables within the script as opposed to creating files, the comment about that the files needing to be hidden made me wonder what you meant until I read what you were doing.

grail's latest post probably is 100% on, but you'll have to test it. Clearly very brief and on the mark. I have little to add insofar as BASH script recommendations.

But, just my personal style, and in conjunction with NevemTeve's comment about using a language. Half on/half off that bandwagon. Yes, I might use C to do this. But also what I'd do if I went down the script option was to segregate the problem and make functions, because you can do that in BASH. I tend to do brute force stuff because I'm not big with sed, awk, or regular expressions, so I use the fundamental stuff and extend mainly when I have to via looking the details up for a complex command.

I've found that you can organize a lengthy, and involved BASH script by using functions and then further, re-use the functions if properly segmented. That's really my point here. A combination of K.I.S.S. along with some re-checking of how you're doing. Try to be simple. Sure some complex problems make for complex solutions, one thing to do is ask for style suggestions as you've done here. The other thing to do is break down your effort in verbiage as well as within code so that you do not end up having a highly involved set of instructions where:

You possibly could look at it in a year and not understand it because it was a one-of which you looked up in order to complete
You can't re-use it either for a similar but different effort because the complex commands are so tightly coupled to a very particular search/replace/action solution
You can't re-use it on a different machine because you chose highly specific command options which aren't always universal from machine to machine.

OK off my soapbox.