How to create argument variable in bash script

Question

I am trying to write a script such that I can identify number of characters of the n-th largest file in a sub-directory. I was trying to assign n and the name of sub-directory into arguments like $1, $2.

Current directory: Greetings
   Sub-directory: language_files, others
     Sub-directory: English, German, French
          Files: Goodmorning.csv, Goodafternoon.csv, Goodevening.csv ….

I would be at directory “Greetings”, while I indicating subdirectory (English, German, French), it would show the nth-largest file in the subdirectory indicated and calculate number of characters as well.

For instance, if I am trying to figure out number of characters of 2nd largest file in English, I did:

langs=$1
n=$2
for langs in language_files/;
 Do count=$(find language_files/$1 name "*.csv" | wc -m | head -n -1 | sort -n -r | sed -n $2(p))
Done | echo "The file has $count bytes!"

The result I wanted was:

$ ./script1.sh English 2
The file has 1100 bytes!

The main problem of all the issue is the fact that I don't understand how variables and looping work in bash script.

So start learning. The script is almost ok. Remainders: bash is case sensitive. for is not For. To grab command output use command substitution. Even with fors! count_bytes=$(for langs in language/*; do echo $langs; done). bash is space sensitive - var='a' will work, but var = 'a' will not! Use wc -c not wc -m, i think it doesn't do what you think. bash uses " not “. And use dynamic programming - split your problem into many little problems. — KamilCuk
– KamilCuk, Commented Jan 28, 2019 at 20:02

karakfa · Accepted Answer · 2019-01-28 21:08:48Z

1

no need for looping

find language_files/"$1" -name "*.csv" | xargs wc -m | sort -nr | sed -n "$2{p;q}"

for byte counting you should use -c, since -m is for char counting (it may be the same for you).

You don't use the loop variable in the script anyway.

answered Jan 28, 2019 at 21:08

karakfa

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3 Comments

David C. Rankin Over a year ago

Always an efficiency benefit from avoiding the loops.

colbyjackson Over a year ago

What does {p;q} mean after $2?

karakfa Over a year ago

Print and quit. To prevent scanning the rest of the lines.

thb · Accepted Answer · 2019-01-28 21:19:09Z

Bash loops are interesting. You are encouraged to learn more about them when you have some time. However, this particular problem might not need a loop. Set lang (you can call it langs if you prefer) and n appropriately, and then try this:

count=$(stat -c'%s %n' language_files/$lang/* | sort -nr | head -n$n | tail -n1 | sed -re 's/^[[:space:]]*([[:digit:]]+).*/\1/')

That should give you the $count you need. Then you can echo it however you like.

EXPLANATION

If you wish to learn how it works:

The stat command outputs various statistics about the named file (or files), in this case %s the file's size and %n the file's name.
The head and tail output respectively the first and last several lines of a file. Together, they select a specific line from the file
The sed command screens a certain part of the line. (You can use cut, instead, if you prefer.)

If you wish to be cleverer, then you can optimize as @karafka has done.

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