Why doesn't my variable seem to increment in my bash while loop?

Question

I am fairly new to bash scripting. I can\'t seem to get the correct value of my counting variables to display at the end of of a while loop in my bash script.

Answer 1

This is because you are using the useless cat command with a pipe, causing a subshell to be created. Try it without the cat:

while read filename ; do
    N=$((N+1))
    ....
done < file

Answer 2

Alternatively, if you want to keep the cat for some reason, you can fix your script simply by adding this line before the cat instruction:

shopt -s lastpipe 

Answer 3

More generally, sometimes you want to pipe the output of a command. Here's an example that uses process substitution to lint JavaScript files about to be committed by Git and counts the number of files that failed:

# $@ glob
git-staged-files() {
  git diff --cached -C -C -z --name-only --relative --diff-filter=ACMRTUXB "$@"
}

# $@ name
map() { IFS= read -rd $'\0' "$@"; }

declare -i errs=0
while map file; do
  echo "Checking $file..."
  git show ":$file"|
  eslint --stdin --stdin-filename "$file" || ((++errs))
done < <(git-staged-files \*.js)

((errs)) && echo -en "\e[31m$errs files with errors.\e[00m " >&2 || :