Bash: Resolving Symlinks to Shellscripts | Comments (3)
Posted in Code, Linux/Unix on 10th October 2008, 2:54 pm by Stuart
Here’s a way to resolve symlinks that call a bash shellscript.
The Problem
I like to be able to use something like this in my bash scripts:
SCRIPTDIR=$(dirname $0)Which is great for a reference to where the script is, but it suffers from the problem that if you symlink to that script $0 now refers to the symlink rather than the actual script.
The Solution
The hack solution is to use the following instead:
function resolve_symlink {
SCRIPT=$1 NEWSCRIPT=''
until [ "$SCRIPT" = "$NEWSCRIPT" ]; do
if [ "${SCRIPT:0:1}" = '.' ]; then SCRIPT=$PWD/$SCRIPT; fi
cd $(dirname $SCRIPT)
if [ ! "${SCRIPT:0:1}" = '.' ]; then SCRIPT=$(basename $SCRIPT); fi
SCRIPT=${NEWSCRIPT:=$SCRIPT}
NEWSCRIPT=$(ls -l $SCRIPT | awk '{ print $NF }')
done
if [ ! "${SCRIPT:0:1}" = '/' ]; then SCRIPT=$PWD/$SCRIPT; fi
echo $(dirname $SCRIPT)
}
DIR=$(resolve_symlink $0)
echo $DIRThis updated version should fix the shortcomings of the previous version pointed out in the first comment by resolving links that are relative as well as link chains. Whilst readlink works for linux systems the script above should be portable across unixes which was the original intention.
If you can rely on python then there’s an even easier way:
DIR=$(python -c "import os; print os.path.realpath(\"${0}\")")
echo $DIRBut again portability is the key.
Find any issues or have improvements to add please let me know.
Good first step, but I see at least two potential issues in it.
1) symlink chains (i.e. l2 symlinks to l1 symlinks to script). If the script is invoked as l2, you’ll get the directory of l1 instead of script.
2) relative symlinks. If the symlink is relative rather then absolute, the directory name you get needs to be interpreted relative to the symlinks directory.
@R Samuel Klatchko: 2 very good points well made!
ON linux I’ve found that infact
readlink -f $0solves all the problems as it resolved relative paths and follows all the links correctly, the downside being mac’s don’t have gnu readlink by default! and the BSD equivalent has barely any functionality (That’s Reason no.343249 to look at moving to Ubuntu for me!)However currently I’d ideally like a solution that works for Mac too. When I work out a portable solution I’ll update the post.
heh. I just came to say: what’s wrong with readlink? Didn’t know it wasn’t on Macs.