How to prevent filename expansion in for loop in bash

Question

In a for loop like this,

for i in `cat *.input`; do
    echo "$i"
done

if one of the input file contains entries like *a, it will, and give the filenames ending in 'a'.

Is there a simple way of preventing this filename expansion?

Because of use of multiple files, globbing (set -o noglob) is not a good option. I should also be able to filter the output of cat to escape special characters, but

for i in `cat *.input | sed 's/*/\\*'`
    ...

still causes *a to expand, while

for i in `cat *.input | sed 's/*/\\\\*'`
    ...

gives me \*a (including backslash). [ I guess this is a different question though ]

Answer 1

This will cat the contents of all the files and iterate over the lines of the result:

while read -r i
do
    echo "$i"
done < <(cat *.input)

If the files contain globbing characters, they won't be expanded. They keys are to not use for and to quote your variable.

In Bourne-derived shells that do not support process substitution, this is equivalent:

cat *.input | while read -r i
do
    echo "$i"
done

The reason not to do that in Bash is that it creates a subshell and when the subshell (loop) exits, the values of variables set within and any cd directory changes will be lost.

Answer 2

For the example you have, a simple cat *.input will do the same thing.