Shell Programming and Scripting

in bash:

Code:

for file in $dir1/* ; do
if [[ "$file" =~ ".txt" ]]; then
echo "Skipping $file (is a txt file)"
fi
done

Code:

for f in $(find . -name "*.txt"); do
    echo Do something with ${f}.
done

Never, ever do that. 'for i in *.txt' is safer and cheaper. Using ls and command substitution means that it's impossible to handle filenames with IFS characters (by default, spaces, tabs, and newlines). Also, if there are very many *.txt files in the directory, a command line length limit imposed by the exec system call may prevent the operating system from successfully launching ls; this is not an issue with the shell pattern glob as it does not require a new process.

Please pass along the cluestick thwack when you see someone else doing the same

Regards,
Alister

Alister is correct that command substitution is expensive in terms of processing resources, but using a simple *.txt will not find the files in sub-directories. See my previous post. Unless you are dealing with thousands of files, the resource constraint should not be a problems.

While I did mention that the sh glob is "cheaper" (which I now regret), please note that my post is about correctness and robustness, not performance.

I wasn't referring to searching subdirectories, only that specific use of ls. It serves absolutely no purpose whatsoever and can only result in mishandled filenames. In such a case, where ls is being used to retrieve the filenames in directories (non-recursively), always use file expansion instead.

While we're here, your find solution is also unable to properly handle any filenames with IFS characters (though it's not constrained by a command length limit if there are very many *.txt files). It could be made to handle spaces and tabs correctly, though not newlines, if instead of using the find in a command substitution in a for loop's list, you piped the output of find into a while read loop.

One last point: Please don't misinterpret my intention. I realize that most of the time technically-limited solutions are more than adequate; I use them all the time myself. I simply highlight the limitations so that anyone who is not aware of them will learn.

Regards,
Alister

@alister, Understood.

The statement I provided should handle special characters in the find and for loop statements. How the files are processed after finding them is up to the code within the for loop. File names should not include new line characters...at least I have yet to encounter one. If you have a suggestion for dealing with such an occurrence, please include it so we can all learn from it.

Thanks.

im trying this in csh but it doesn't seem to work.

btw
im checking the second parameter, like this

if($argv[2] == "-r") then

search in all the sub-folders of that folder

endif