Hacker News new | ask | show | jobs
by unqueued 631 days ago
If you are iterating over a lot of files, a read while loop can be a major bottleneck. As long as you use the null options from find and pipe into xargs, you should be safe with any filename.

I've found it can reduce minutes down to seconds for large operations.

If you have to process a large number of files, you can let xargs minimize the number of times a program is run, instead of running it once per file.

Something like:

  # Set the setgid bit for owner and group of all folders
  find . -type d -print0 | xargs -0 chmod g+s

  # Make the targets of symlinks immutable
  find . -type l -print 0 | xargs -0 readlink -z | xargs -0 chattr +i
Way faster. But there are lots of caveats. Make sure your programs support it. Maybe read the xargs man page.
1 comments
amiga386 631 days ago
Personally I skip the middleman when I can with "find ... -exec cmd {} +"

    find . -type d -exec chmod g+s {} +
Or even minimise arguments by including a test if the chmod is even needed:

    find . -type d \! -perm -g=s -exec chmod g+s {} +
I actually have a script that fixes up permissions, and I was delighted to fit it in a single find invocation which only performs a single stat() on each file in the traversal, and only executes chown/chmod at all for files that need change:

    # - ensure owner is root:shared
    # - ensure dirs have 775 permissions (must have 775, must not have 002)
    # - ensure files have 775 (if w+x), 664 (if w), 555 (if x) otherwise 444 permissions
    find LIST OF DIRS \
        '(' \! '(' -user root -group shared ')'              -print -exec chown -ch root:shared {} + ')' , \
        '(' -type d \! '(' -perm -775 \! -perm -002 ')'      -print -exec chmod -c 775 {} + ')' , \
        '(' -type f    -perm /222    -perm /111 \! -perm 775 -print -exec chmod -c 775 {} + ')' , \
        '(' -type f    -perm /222 \! -perm /111 \! -perm 664 -print -exec chmod -c 664 {} + ')' , \
        '(' -type f \! -perm /222    -perm /111 \! -perm 555 -print -exec chmod -c 555 {} + ')' , \
        '(' -type f \! -perm /222 \! -perm /111 \! -perm 444 -print -exec chmod -c 444 {} + ')'
But if you need multiple transformations of filenames in a pipeline like in your second example, then yes xargs will be involved.
link