Shell Metacharacters – How to Escape Shell Metacharacters Automatically with Find Command

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I've got a bunch of XML files under a directory tree which I would like to move to corresponding folders with the same name within that same directory tree.

Here is sample structure (in shell):

touch foo.xml bar.xml "[ foo ].xml" "( bar ).xml"
mkdir -p foo bar "foo/[ foo ]" "bar/( bar )"

So my approach here is:

find . -name "*.xml" -exec sh -c '
  DST=$(
    find . -type d -name "$(basename "{}" .xml)" -print -quit
  )
  [ -d "$DST" ] && mv -v "{}" "$DST/"' ';'

which gives the following output:

‘./( bar ).xml’ -> ‘./bar/( bar )/( bar ).xml’
mv: ‘./bar/( bar )/( bar ).xml’ and ‘./bar/( bar )/( bar ).xml’ are the same file
‘./bar.xml’ -> ‘./bar/bar.xml’
‘./foo.xml’ -> ‘./foo/foo.xml’

But the file with square brackets ([ foo ].xml) hasn't been moved as if it had been ignored.

I've checked and basename (e.g. basename "[ foo ].xml" ".xml") converts the file correctly, however find has problems with brackets. For example:

find . -name '[ foo ].xml'

won't find the file correctly. However, when escaping the brackets ('\[ foo \].xml'), it works fine, but it doesn't solve the problem, because it's part of the script and I don't know which files having those special (shell?) characters. Tested with both BSD and GNU find.

Is there any universal way of escaping the filenames when using with find's -name parameter, so I can correct my command to support files with the metacharacters?

Best Answer

It's so much easier with zsh globs here:

for f (**/*.xml(.)) (mv -v -- $f **/$f:r:t(/[1]))

Or if you want to include hidden xml files and look inside hidden directories like find would:

for f (**/*.xml(.D)) (mv -v -- $f **/$f:r:t(D/[1]))

But beware that files called .xml, ..xml or ...xml would become a problem, so you may want to exclude them:

setopt extendedglob
for f (**/(^(|.|..)).xml(.D)) (mv -v -- $f **/$f:r:t(D/[1]))

With GNU tools, another approach to avoid having to scan the whole directory tree for each file would be to scan it once and look for all directories and xml files, record where they are and do the moving in the end:

(export LC_ALL=C
find . -mindepth 1 -name '*.xml' ! -name .xml ! \
  -name ..xml ! -name ...xml -type f -printf 'F/%P\0' -o \
  -type d -printf 'D/%P\0' | awk -v RS='\0' -F / '
  {
    if ($1 == "F") {
      root = $NF
      sub(/\.xml$/, "", root)
      F[root] = substr($0, 3)
    } else D[$NF] = substr($0, 3)
  }
  END {
    for (f in F)
      if (f in D) 
        printf "%s\0%s\0", F[f], D[f]
  }' | xargs -r0n2 mv -v --
)

Your approach has a number of problems if you want to allow any arbitrary file name:

embedding {} in the shell code is always wrong. What if there's a file called $(rm -rf "$HOME").xml for instance? The correct way is to pass those {} as argument to the in-line shell script (-exec sh -c 'use as "$1"...' sh {} \;).
With GNU find (implied here as you're using -quit), *.xml would only match files consisting of a sequence of valid characters followed by .xml, so that excludes file names that contain invalid characters in the current locale (for instance file names in the wrong charset). The fix for that is to fix the locale to C where every byte is a valid character (that means error messages will be displayed in English though).
If any of those xml files are of type directory or symlink, that would cause problems (affect the scanning of directories, or break symlinks when moved). You may want to add a -type f to only move regular files.
Command substitution ($(...)) strips all trailing newline characters. That would cause problems with a file called foo␤.xml for instance. Working around that is possible but a pain: base=$(basename "$1" .xml; echo .); base=${base%??}. You can at least replace basename with the ${var#pattern} operators. And avoid command substitution if possible.
your problem with file names containing wildcard characters (?, [, * and backslash; they are not special to the shell, but to the pattern matching (fnmatch()) done by find which happens to be very similar to shell pattern matching). You'd need to escape them with a backslash.
the problem with .xml, ..xml, ...xml mentioned above.

So, if we address all of the above, we end up with something like:

LC_ALL=C find . -type f -name '*.xml' ! -name .xml ! -name ..xml \
  ! -name ...xml -exec sh -c '
  for file do
    base=${file##*/}
    base=${base%.xml}
    escaped_base=$(printf "%s\n" "$base" |
      sed "s/[[*?\\\\]/\\\\&/g"; echo .)
    escaped_base=${escaped_base%??}
    find . -name "$escaped_base" -type d -exec mv -v "$file" {\} \; -quit
  done' sh {} +

Phew...

Now, it's not all. With -exec ... {} +, we run as few sh as possible. If we're lucky, we'll run only one, but if not, after the first sh invocation, we'll have moved a number of xml files around, and then find will continue looking for more, and may very well find the files we have moved in the first round again (and most probably try to move them where they are).

Other than that, it's basically the same approach as the zsh ones. A few other notable differences:

with the zsh one, the file list is sorted (by directory name and file name), so the destination directory is more or less consistent and predictable. With find, it's based on the raw order of files in directories.
with zsh, you'll get an error message if no matching directory to move the file to is found, not with the find approach above.
With find, you'll get error messages if some directories cannot be traversed, not with the zsh one.

A last note of warning. If the reason you get some files with dodgy file names is because the directory tree is writable by an adversary, then beware than none of the solutions above are safe if the adversary may rename files under the feet of that command.

For instance, if you're using LXDE, the attacker could make a malicious foo/lxde-rc.xml, create a lxde-rc folder, detect when you're running your command and replace that lxde-rc with a symlink to your ~/.config/openbox/ during the race window (which can be made as large as necessary in many ways) between find finding that lxde-rc and mv doing the rename("foo/lxde-rc.xml", "lxde-rc/lxde-rc.xml") (foo could also be changed to that symlink making you move your lxde-rc.xml elsewhere).

Working around that is probably impossible using standard or even GNU utilities, you'd need to write it in a proper programming language, doing some safe directory traversal and using renameat() system calls.

All the solutions above will also fail if the directory tree is deep enough that the limit on the length of the paths given to the rename() system call done by mv is reached (causing rename() to fail with ENAMETOOLONG). A solution using renameat() would also work around the problem.

Related Solutions

Find command for lookup up a directory tree

The following uses find and would still search from the root directory down to the current directory, but would only look inside the directories on that single path:

find / -exec bash -c '[[ $PWD != "$1"* ]]' bash {} \; -prune -name foo -print

The first part of the command, up to the -prune, will determine whether the current pathname being examined is located in the path of $PWD. If it's not on the way to the current directory, it is pruned from the search path.

The comparison is carried out by a very short bash script that simply tests whether the current directory, $PWD, matches the start of the current pathname.

The bit after -prune simply tries to match foo against the filename that is being examined.

Example: Trying to find something called bin somewhere in the directory structure above where I'm currently at.

$ pwd
/home/kk/local/build/ast/build/src/cmd/ksh93/sh

$ find / -exec bash -c '[[ $PWD != "$1"* ]]' bash {} \; -prune -name bin -print
/bin
/home/kk/local/bin
/home/kk/local/build/ast/bin

On systems without bash, or where there is a faster-to-start sh shell:

find / -exec sh -c 'case $PWD in ("$1"*) exit 1; esac' sh {} \; -prune -name bin -print

Find 2 files with similar names and move them to a new location

The simplest approach will depend on how much you can trust your users. If you don't need to test that both files exist or that the names are correct or anything, you don't even need a script. You can do this with a simple find:

find /dir/to/source -name "ABC*" -mmin +5 -exec mv {} /destination/dir \;

If you need to make sure that i) both files are there and ii) both have a modification time of at least 5 minutes ago, on a GNU system, you could do this:

#!/usr/bin/env bash

SOURCEDIR="/dir/to/source"
DESTDIR="/destination/dir"

for f in "${SOURCEDIR}"/*.xml; do
    ## Make sure the file exists and is a regular file (or symlink to regular file),
    ## and that its modification date is at least 5 minutes ago
    [ -f "$f" ] && [ "$(( $(date +%s) - $(stat -c %Y "$f") ))" -ge 300 ] || continue

    ## Do the same for a file of the same name but with the .mxf extension.
    mxf="${SOURCEDIR}/$(basename "$f" .xml).mxf";
    [ -f "$mxf" ] && [ "$(( $(date +%s) - $(stat -c %Y "$no_ext") ))" -ge 300 ] || continue

    ## We will only get to this point if all of the above tests were successful
    echo mv -v "$f" "$mxf" "$DESTDIR"
done

Best Answer

Related Solutions

Find command for lookup up a directory tree

Find 2 files with similar names and move them to a new location

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