How to skip line with comment (# space ) in bash for loop

Question

With the following code:

#!/bin/bash
export LC_ALL=C

for input_file in $(<inputflist.txt)
do
    case "$input_file" in \#*) continue ;; esac
    echo $input_file

done

And inputflist.txt with the following content:

# foo.txt
bar.txt

I expect it to just print the last line bar.txt but it prints this instead:

foo.txt
bar.txt

What's the right way to do it?

anubhava · Accepted Answer · 2015-07-14T06:01:21.780

3

This should work:

while IFS= read -r line; do
   [[ $line =~ ^[[:blank:]]*# ]] && continue
   echo "$line"
done < inputflist.txt

Output:

bar.txt

edited Jul 14 '15 at 06:01

answered Jul 13 '15 at 14:43

anubhava

1

`[[:blank:]]*` is useless here, `$line` doesn't have the leading white spaces, it loses any indentation here (as `IFS` isn't set properly). So deleting that part of the regex will yield to same result. – Jahid Jul 14 '15 at 04:02
1

That's right, thanks for your comment. It needs `IFS=` before `read` to preserve whitespace. – anubhava Jul 14 '15 at 06:02

Jahid · Answer 2 · 2015-07-14T04:13:11.950

3

Don't read lines with for, use a while loop instead:

while IFS= read -r line;do
[[ $line =~ ^[[:space:]]*# ]] || echo "$line"
done <file

Note:

edited Jul 14 '15 at 04:13

answered Jul 13 '15 at 14:45

Jahid

`[[:space:]]` also matches newlines – anubhava Jul 13 '15 at 14:52
@anubhava that doesn't make any difference here, does it? – Jahid Jul 13 '15 at 14:55
1

That was just a **fyi comment**. Yes it won't impact this script since `$line` doesn't have any newlines. – anubhava Jul 13 '15 at 14:56
I like the OP's `case` statement better than the `[[` regex, though. – tripleee Jul 14 '15 at 03:29
@tripleee that case method won't delete indented lines. – Jahid Jul 14 '15 at 03:42
1

True; the regex facility allows for a more versatile expression. – tripleee Jul 14 '15 at 03:44

score 2 · Answer 3 · answered Jul 13 '15 at 15:12

2

what's wrong in

for input_file in $(grep -v "^#" inputflist.txt); do
  echo $input_file
done

or simply

grep -v "^#" inputflist.txt

?

answered Jul 13 '15 at 15:12

Maduraiveeran

https://mywiki.wooledge.org/DontReadLinesWithFor explains what's wrong with the first one. The second is fine. – tripleee Mar 28 '19 at 16:25
Oh and in the first, your quoting is broken, too; [When to wrap quotes around a shell variable?](https://stackoverflow.com/questions/10067266/when-to-wrap-quotes-around-a-shell-variable) – tripleee Mar 28 '19 at 16:39

3 Answers3