linuxbashshellreadlink

readlink command misbehave after issueing pushd command in bash scripts

I came across one complex problem I tried to explain it with simple example as below

In my system I have

ubuntu@ubuntu:~/temp$ pwd
/home/ubuntu/temp
ubuntu@ubuntu:~/temp$ ls
temp1  test.sh
ubuntu@ubuntu:~/temp$

In temp.sh I have

#!/bin/bash

echo "Arg 0 = $0"
echo "Arg 1 = $1"
echo "Arg 0 Full Path $(readlink -f $0)"
echo "Arg 1 Full Path $(readlink -f $1)"
pushd /var/log
echo "Arg 0 = $0"
echo "Arg 1 = $1"
echo "Arg 0 Full Path $(readlink -f $0)"
echo "Arg 1 Full Path $(readlink -f $1)"

now I run at below way

ubuntu@ubuntu:~/temp$ ./test.sh temp1
Arg 0 = ./test.sh
Arg 1 = temp1
Arg 0 Full Path /home/ubuntu/temp/test.sh
Arg 1 Full Path /home/ubuntu/temp/temp1
/var/log ~/temp
Arg 0 = ./test.sh
Arg 1 = temp1
Arg 0 Full Path /var/log/test.sh
Arg 1 Full Path /var/log/temp1

Here you can see readlink shows wrong path of the Arg0 and Arg1 files after issuing pushd command. If I remove popd command then it prints fine.

So why here readlink misbehave?

Solution

  • Given relative paths, readlink will interpret them relative to process working directory, and output absolute paths (resolving symbolic links inbetween).

    The key point here is the process working directory (aka current directory).

    So readlink ./path/to/file will output /tmp/path/to/file if /tmp is the current directory (supposing no symbolic links).

    The other command you're using, pushd will change the process working directory.

    So in the sequence

    readlink ./path/to/file
pushd /some/other/place
readlink ./path/to/file

    both readlink will likely resolve to two different absolute paths.

    No misbehavior here. All by design.