Bash paths calculation

Question

I would like to know why in order to get current directory from within a script we need to use solution such as:DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )" taken from here.
Instead of something like:
DIR=$("pwd")
Once I have current directory of current script, and I want to calculate its parent's parent parent directory path, how do I do that? In terminal its simply cd ../../../, how this can be caluclated on DIR and assigned to a new variable?
What is the difference in bash assignment between NUM:=1 and NUM=1

Cheers

You should ask 3 questions as 3 separate questions. Which answer will you flag as correct if there are 3 different answers, one for each question? — choroba, Nov 15 '17 at 19:36

score 2 · Accepted Answer · answered Nov 15 '17 at 19:43

2

That's not the current directory, but the directory where the script is located. Other similar solutions are readlink -f "${0%/*}" etc.
You can add the double dots to the DIR:
```
great_grand_parent=$DIR/../../..
```
Call readlink or do the magic with cd to get rid of the double dots.
NUM:=1 is not an assignment at all.

answered Nov 15 '17 at 19:43

choroba

Thanks. About 3, what is it? – JavaSa Nov 15 '17 at 19:49
`bash: NUM:=1: command not found`. So unless you have an executable file of such a name, it's a syntax error. – choroba Nov 15 '17 at 19:54
Ok my mistake lets ask it for `SOME_PATH:=/var/log` vs `SOME_PATH=/var/log` – JavaSa Nov 15 '17 at 20:14
By the way as for question 1, can you please explain a bit the difference between my suggestion and solution from other thread? I'm not sure I understand the difference – JavaSa Nov 15 '17 at 20:17
@JavaSa That's still not an assignment: "-bash: SOME_PATH:=/var/log: No such file or directory". – Gordon Davisson Nov 15 '17 at 20:26
By the way solution 2 doesn't work for me, are you sure it works? – JavaSa Nov 15 '17 at 20:45
@JavaSa: Your suggestion returns the current directory, the other solution returns the directory where the script is located. – choroba Nov 15 '17 at 23:12
@JavaSa: What do you mean by "doesn't work"? What's in $DIR, what's in the other variable? – choroba Nov 15 '17 at 23:13

1 Answers1