Mdthbs

Is there a non-recursive readlink -f / realpath alternative, that outputs absolute symlink destinations? A more POSIX compatible solution is welcome as well.

I have a function block in my shell script as follows:

set FILES

# addFile adds a file to the FILES list. If file is a symlink,

# it will also find and add the destination.

addFile() {

    file="$1"

    # Check if file is already included in list

    echo "$FILES" | grep -q "$file" && return

    FILES="$FILES $file"

    if [ -L $file ]; then

        addFile $(realpath $file)

        #addFile $(readlink $file)

    fi

}

I'm using this function in a script which is collecting binary and library files from around the file system. But I foresee a problem in this code:

1. My first try I used readlink, but this returned symlink resolution paths relative to the $file, thus any actions performed on those paths fail. (Now commented out, but still in code) (See minor edit below)


2. After that, I used realpath instead, as suggested by man readlink. It almost works.

Now, the actions that I want to perform can work. However, in the final result I'm copying over all the binaries, libraries and symlinks in an initramfs. If there are any recursive symlinks, only the top level and the destination will be included, not the intermediate ones. Thus, breaking the symlink.

I've created a fiddle to demonstrate the issue. link-to-link1 points to link1, which points to file1. In the end result link1 is missing and link-to-link1 is broken.

Edit; clarify the issue

When running the above function on the following set of symlinks:

# Contents of ~/test/src

file0

file1

link0 -> file0

link0.1 -> file0

link1 -> file1

link-to-link1 -> link1

With:

copy="link-to-link1 link0 link0.1"

for sf in $copy; do

    addFile ~/test/src/$sf

done;

cp -av $FILES ~/test/dst

You will find that only the 3 links from $copy and 2 files are copied. However, intermediate link link1 is missing and link-to-link1 is broken.

I would like the script to find link1 as well. Keeping in mind that in the environment where this script is run, the location of files and symlinks have to be absolute.

Minor edit

Add another fiddle to demonstrate failing of relative paths, using readlink. Only the symlinks are copied and the destinations are missing.

If I understand right, for the example given, you want link1 for the file link-to-link1. That you can get using GNU find's -printf and %l:

$ find . -type l -printf '%p -> %ln'

./link0.1 -> file0

./link1 -> file1

./link0 -> file0

./link-to-link1 -> link1

Since the absolute path of link1 is needed as the output for /path/to/link-to-link1, maybe cd to the directory containing link-to-link1 and run readlink/realpath in succession:

(

cd "$(dirname "$file")"

realpath -s "$(readlink "$file")"

)

realpath -s does not resolve symbolic links, but will print the absolute path.

For example:

~ file=/tmp/foo/link-to-link1

~ (cd "$(dirname "$file")"; realpath -s "$(readlink "$file")")

/tmp/foo/link1

This will also work for links to absolute paths:

~ file=/tmp/foo/link2

~ ln -sfv /tmp/foo/link1 "$file"

'/tmp/foo/link2' -> '/tmp/foo/link1'

~ (cd "$(dirname "$file")"; realpath -s "$(readlink "$file")")

/tmp/foo/link1