Bash scope issue (?) when incrementing variable

Question

I have code like this:

#!/bin/bash

n=0
for file in *.txt
do
        tail -c1 $file | read -r _ || (
                ((n++))
                echo "$file is missing a final newline, issue #$n"
        )
done

But when I run it, the numbers aren't incrementing:

a.txt is missing a final newline, issue #1

b.txt is missing a final newline, issue #1

How can I fix this? It looks like a scope issue, since the 0 is incremented to 1 as though the previous increment was ignored.

Not related to your question, but the code will fail if a filename contains whitespace, using double-quotes is much safer: tail -c1 "$file". — cdarke
– cdarke, Commented May 10, 2016 at 19:40
@cdarke: Good point! In my actual use case I'm using a more specific glob which doesn't permit spaces, but that should be useful for future visitors to this question. :) — Charles
– Charles, Commented May 10, 2016 at 20:01

karakfa · Accepted Answer · 2016-05-10 19:00:24Z

1

your commands embedded between parentheses runs as a subshell, each subshell in the loop starts over with the value of n set at the parent level (n=0).

Just change the parenthesis to curly braces (a terminal semicolon or newline is required).

answered May 10, 2016 at 19:00

karakfa

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2 Comments

Charles Over a year ago

That's it! Such a simple thing to miss, thanks for spotting it.

rici Over a year ago

Or just use a single command: `... || echo "$file is missing a final newline, issue #$((++n))"

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