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bashshellfor-loopwildcardexpansion
cagri
cagri

Reputation: 43

How to prevent filename expansion in for loop in bash

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 ]

Upvotes: 4

Views: 1507

Answers (2)

Dennis Williamson
Dennis Williamson

Reputation: 360615

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.

Upvotes: 5

Satya
Satya

Reputation: 4478

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

Upvotes: 0

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