In this post, I will show bash commands pushd and popd.
Bash shell has one functionality that is not widely known - this functionality is directory stack.
As the name suggests, it's a stack where one can store directories, and on top of that stack is stored current directory.
Before we learn how this stack works, let's take a look at the commands to operate it:
- pushd - is used for adding directories to the stack
- popd - is used for removing directories from the stack
- dirs - is used for displaying directories on the stack
We're going to learn how to use stack but examples :)
First, let's display the current stack content:
torgiren@redraptor ~ $ dirs -v
0 ~
torgiren@redraptor ~ $ cd /tmp
torgiren@redraptor /tmp $ dirs -v
0 /tmp
We can see, that dirs -v prints out the content of the stack, which but the default has only one item - current directory
Next, let's add some directory on top of the stack
torgiren@redraptor /tmp $ pushd /proc/
/proc /tmp
torgiren@redraptor /proc $ dirs -v
0 /proc
1 /tmp
We can see, that /proc directory was added on top and /tmp was moved to the second position. Also, the current directory was changed to /proc. As I said before, the current directory is on top of the stack, that's why adding /proc on top we changed the current directory
After the traditional change directory, we can see that:
torgiren@redraptor /proc $ cd /sys
torgiren@redraptor /sys $ dirs -v
0 /sys
1 /tmp
the top element was changed
Next, let's try to pop the top element:
torgiren@redraptor /sys $ popd
/tmp
torgiren@redraptor /tmp $ dirs -v
0 /tmp
what happened here...
popd command popped the top element, that's why the second element became the top element and that changed current directory to /tmp.
With this knowledge, we can move to real-life example (one of the two I use most often)
torgiren@redraptor /tmp $ pushd .
/tmp /tmp
torgiren@redraptor /tmp $ dirs -v
0 /tmp
1 /tmp
torgiren@redraptor /tmp $ cd /etc
torgiren@redraptor /etc $ cd conf.d
torgiren@redraptor /etc/conf.d $ pwd
/etc/conf.d
torgiren@redraptor /etc/conf.d $ cd ..
torgiren@redraptor /etc $ cd init.d/
torgiren@redraptor /etc/init.d $ popd
/tmp
torgiren@redraptor /tmp $ dirs -v
0 /tmp
what's going on here...
When I was in /tmp directory, I pushed on the stack the current directory - /tmp. As a result, I had /tmp twice on the stack. Next, I changed the directories to /etc, /ecp/conf.d, /etc/init.d. As we know, cd change only the top element, what that's why there's /tmp still on position 1. After finishing work in /etc directories, I used popd to pop the top element, and position 1 became position 0, so I backed to the /tmp directory. It's the improved version of cd -, because cd - allows to back only to the last directory and using stack allows to make any number of dir changes and then back to remembered position.
We can also use pushd -n to add items on the stack without changing the current directory. It is added to the second position then.
torgiren@redraptor /tmp $ cd /tmp/
torgiren@redraptor /tmp $ mkdir -p pushd/a1
torgiren@redraptor /tmp $ mkdir -p pushd/a2
torgiren@redraptor /tmp $ mkdir -p pushd/a3
torgiren@redraptor /tmp $ cd pushd/
torgiren@redraptor /tmp/pushd $ touch a1/test.txt
torgiren@redraptor /tmp/pushd $ touch a1/test2.txt
torgiren@redraptor /tmp/pushd $ touch a1/test3.txt
torgiren@redraptor /tmp/pushd $ pushd -n a1
/tmp/pushd a1
torgiren@redraptor /tmp/pushd $ pushd -n a2
/tmp/pushd a2 a1
torgiren@redraptor /tmp/pushd $ pushd -n a3
/tmp/pushd a3 a2 a1
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
1 a3
2 a2
3 a1
With stack like this, we can go to the second functionality most often used by me.
Let's say we want to move test2.txt file to a2 directory, and test3.txt to a3. Instead of the standard mv a1/test2.txt a2 we can do:
torgiren@redraptor /tmp/pushd $ mv ~3/test2.txt ~2/ -iv
przemianowany 'a1/test2.txt' -> 'a2/test2.txt'
torgiren@redraptor /tmp/pushd $ mv ~3/test3.txt ~1/ -iv
przemianowany 'a1/test3.txt' -> 'a3/test3.txt'
At first glance it can not seems like a big improvement to standard mv, but let's take a look at a real-life example:
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
torgiren@redraptor /tmp/pushd $ pushd .
/tmp/pushd /tmp/pushd
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
1 /tmp/pushd
torgiren@redraptor /tmp/pushd $ cd /etc/
torgiren@redraptor /etc $ cd conf.d/
torgiren@redraptor /etc/conf.d $ cd ..
torgiren@redraptor /etc $ cd init.d/
torgiren@redraptor /etc/init.d $ cp mdadm ~1/a3/ -iv
'mdadm' -> '/tmp/pushd/a3/mdadm'
torgiren@redraptor /etc/init.d $ dirs -v
0 /etc/init.d
1 /tmp/pushd
torgiren@redraptor /etc/init.d $ popd
/tmp/pushd
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
why I find this example to be useful? Because at any stage I don't need to know the exact file path of source nor destination. When talking about the destination, we store current directory on stack, and with source, we can navigate between directories looking for the expected file. And then, in an easy way we can return to the primary directory.
The next thing we can do with the directory stack is to rotate it.
It lets you change directories without removing them from the stack. Direction and step that the stack should be rotated are passed as argument in the format +/-num instead of a directory.
torgiren@redraptor /tmp/pushd/a2 $ pushd -n /tmp/pushd/a3
/tmp/pushd/a2 /tmp/pushd/a3
torgiren@redraptor /tmp/pushd/a2 $ pushd -n /tmp/pushd/a2
/tmp/pushd/a2 /tmp/pushd/a2 /tmp/pushd/a3
torgiren@redraptor /tmp/pushd/a2 $ cd /tmp/pushd/a1/
torgiren@redraptor /tmp/pushd/a1 $ dirs -v
0 /tmp/pushd/a1
1 /tmp/pushd/a2
2 /tmp/pushd/a3
torgiren@redraptor /tmp/pushd/a1 $ pwd
/tmp/pushd/a1
torgiren@redraptor /tmp/pushd/a1 $ pushd +1
/tmp/pushd/a2 /tmp/pushd/a3 /tmp/pushd/a1
torgiren@redraptor /tmp/pushd/a2 $ pwd
/tmp/pushd/a2
torgiren@redraptor /tmp/pushd/a2 $ pushd +1
/tmp/pushd/a3 /tmp/pushd/a1 /tmp/pushd/a2
torgiren@redraptor /tmp/pushd/a3 $ pwd
/tmp/pushd/a3
torgiren@redraptor /tmp/pushd/a3 $ pushd +1
/tmp/pushd/a1 /tmp/pushd/a2 /tmp/pushd/a3
The last but one thing which we can do with the stack is to remove specified elements from it. Because popd let us remove not only the top element but also any other. To specify the item to remove we have to specify it by passing number with direction + or - which means that we want to count from the top or the bottom. Ex. let's remove from stack elements a5, a15, a20, a1, a19.
torgiren@redraptor /tmp/pushd $ for i in $(seq 1 20); do pushd -n a$i; done
/tmp/pushd a1
/tmp/pushd a2 a1
/tmp/pushd a3 a2 a1
/tmp/pushd a4 a3 a2 a1
/tmp/pushd a5 a4 a3 a2 a1
/tmp/pushd a6 a5 a4 a3 a2 a1
/tmp/pushd a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a17 a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a18 a17 a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a19 a18 a17 a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
/tmp/pushd a20 a19 a18 a17 a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
1 a20
2 a19
3 a18
4 a17
5 a16
6 a15
7 a14
8 a13
9 a12
10 a11
11 a10
12 a9
13 a8
14 a7
15 a6
16 a5
17 a4
18 a3
19 a2
20 a1
torgiren@redraptor /tmp/pushd $ popd -4 # a5
/tmp/pushd a20 a19 a18 a17 a16 a15 a14 a13 a12 a11 a10 a9 a8 a7 a6 a4 a3 a2 a1
torgiren@redraptor /tmp/pushd $ popd +6 # a15
/tmp/pushd a20 a19 a18 a17 a16 a14 a13 a12 a11 a10 a9 a8 a7 a6 a4 a3 a2 a1
torgiren@redraptor /tmp/pushd $ popd +1 # a20
/tmp/pushd a19 a18 a17 a16 a14 a13 a12 a11 a10 a9 a8 a7 a6 a4 a3 a2 a1
torgiren@redraptor /tmp/pushd $ popd -0 # a1
/tmp/pushd a19 a18 a17 a16 a14 a13 a12 a11 a10 a9 a8 a7 a6 a4 a3 a2
torgiren@redraptor /tmp/pushd $ popd +1 # a19
/tmp/pushd a18 a17 a16 a14 a13 a12 a11 a10 a9 a8 a7 a6 a4 a3 a2
And the last operation we can find useful I to clear the stack leaving only current directory. We use dirs -c command to achieve that
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
1 a18
2 a17
3 a16
4 a14
5 a13
6 a12
7 a11
8 a10
9 a9
10 a8
11 a7
12 a6
13 a4
14 a3
15 a2
torgiren@redraptor /tmp/pushd $ dirs -c
torgiren@redraptor /tmp/pushd $ dirs -v
0 /tmp/pushd
TORGiren DevOpses