How do I reuse the last output from the command line?

Question

I'd like to know how to reuse the last output from the console, ie:

pv-3:method Xavier$ python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"
/Library/Python/2.6/site-packages
pv-3:method Xavier$ cd **LASTOUTPUT**

Answer 1

Assuming history expansion is enabled, that you're running Bash or some other shell that supports it, that the command is idempotent, and that waiting for it to run a second time is not an issue, you could use the !! form of history expansion to get the last command line again, to run the previous command again in a command substitution:

% python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"
/usr/lib/python2.7/site-packages
% cd $(!!)
cd $(python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()")
% pwd
/usr/lib/python2.7/site-packages

Answer 2

Not yet mentioned, use a variable:

dir=$( python -c ... )
cd "$dir"

Answer 3

All the other solutions involve modifying your workflow or running the command twice, which might not be suitable if it takes a long time to run, or is not repeatable (e.g. it deletes a file - rerunning it would produce a different result).

So here's a more complicated idea if you need it:

.bashrc

exec > >(tee -a ~/$$.out)

PROMPT_COMMAND='LASTLINE=$(tail -n 1 ~/$$.out)'

trap 'rm ~/$$.out' EXIT

bash prompt

$ python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"
/usr/lib/python2.6/dist-packages
$ cd $LASTLINE
$ pwd
/usr/lib/python2.6/dist-packages

This has some issues, so it's just meant as a starting point. For example, the output file (~/<pid>.out) might grow very large and fill up your disk. Also, your whole shell could stop working if tee dies.

It could be modified to only capture the output from the previous command using preexec and precmd hooks in zsh, or an emulation of them in bash, but that's more complicated to describe here.

Answer 4

A working draft for a traditional shell:

ttyid=$(readlink /proc/$$/fd/1)
\___/   \______/ \___/ |  |  |
  |         |      |   |  |  \- 0: stdin 
  |         |      |   |  |     1: stdout <- our interest
  |         |      |   |  |     2: stderr
  |         |      |   |  \- fd is, maybe, filedescriptor
  |         |      |   |
  |         |      |   \- $$ is the PID of the current process (shell,
  |         |      |      in our case)
  |         |      |
  |         |      \- you know, much runtime stuff is here
  |         |
  |         \- readlink extracts the symbolic link of /proc/$$/fd/1
  |            lrwx------ 1 stefan stefan 64 2011-03-18 09:11
  |            /proc/22159/fd/1 -> /dev/pts/4
  |
  \- /dev/tty3 for real shell, /dev/pts/3 for xterm

Now we can cat the screen to a file. Needs sudo.

id=${ttyid//\/dev\/tty}
sudo cat /dev/vcs$id > screen.dump

Apropos screendump: so named program doesn't work for me any more. Maybe for older kernels only. /dev/pts/N didn't work for me too. Maybe you have to some optional MKDEV in /dev - I remember darkly about some /dev/cuaN, but I may be wrong.

We would like to pipe the output instead of using screen.dump. But somehow it doesn't work - sometimes it waits for ENTER.

The capturing isn't a normal textfile with linefeeds, but with - for example - 80x50 chars in one sequence.

To pick the last 2 lines, 1 for the output of the command, and one for the prompting line, I revert it, pick 160 chars, revert again and pick 80.

rev vcs4.dat | sed 's/\(.\{160\}\).*/\1/g' | rev | sed 's/\(.\{80\}\).*/\1/g'

Just in case you ever wondered, why there is a rev program.

Critique:

• The first commands are entered, thus moving the line ahed. Well - just a numerical excercise to pick the 3rd-last line or something. I worked mainly in a different window.
• Not everybody has a 80x50 screen. Well, yes, we know. There is $COLUMNS and $ROWS for your pleasure.
• The output is not allways at the bottom. A fresh and young shell might be in the upper rows. Well - simple as that: Evaluate what shell is running. Which prompt is used. Do some prompt detection and find the last line with a shell-prompt. The line before (or 2. before) should contain the directory.

The first diagram is made with explain.py

Answer 5

Try this:

$ cd $(python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()")
$ pwd
/Library/Python/2.6/site-packages

Answer 6

So, uh, here's an answer:

If you're running under X, select the output you want with the mouse to copy it, and then middle-click to paste it.

If you're running on a text console, you can do a similar thing with gpm.

Answer 7

(It's not a working answer, unfortunately, but still something curious. Someone interested could well try to complete the implementation of the feature I'm going to tell you about.)

In eshell inside Emacs, they wanted to have such a feature but it's not implemented in a complete way (which is however reflected in the documentation).

For example:

~ $ pwd
~
~ $ /bin/echo $$
~
~ $ /bin/pwd
/home/imz
~ $ /bin/echo $$

~ $ 

You see, only the output of builtins can be captured into the $$ variable.

But well, some elisp programming (cf. eshell-mark-output implementation in "esh-mode.el"), and you could implement a function that "marks" the last output and returns it as the function's result; so that you can use that function in a eshell command you are asking for -- elisp functions can be used in eshell commands with the usual elisp syntax, i.e. in parentheses, like this:

~ $ /bin/echo (buffer-name)
*eshell*
~ $ /bin/echo (car '(a b c))
a
~ $ 

Answer 8

There is a better solution:

Just print !! after executed command and you will get repeated output.

E.g.

Original:

https://askubuntu.com/questions/324423/how-to-access-the-last-return-value-in-bash

Answer 9

$ cd \`python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"\`

will do the trick.

Read here for more details: Command substitution.

Answer 10

If you realize you're going to want to reuse the output before you hit Enter, you can save it in a variable: add tmp=$( at the beginning of the line and ) at the end. (This removes any blank line at the end of the command output, and in fact removes any final newline; this rarely matters.)

tmp=$(python -c …)
echo "$tmp"
cd "$tmp"

If your shell is ksh or zsh, here's a useful function you can use to make this more automatic. (It's no help in bash because it requires the last command in a pipeline to be executed in the parent shell, which is only the case in ksh (not pdksh) and zsh.)

keep () {
  local line IFS=$'\n'
  kept=
  while read -r line; do
    printf '%s\n' "$line"
    kept=$kept$line$IFS
  done
}
alias keep=k

Use it this way:

python -c … |k
cd $kept

Answer 11

cd $(python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()" | tee $(readlink /proc/$$/fd/1))

(building up on 4485's answer)

That's lots of typing, so make an alias:

alias tee2tty='tee $(readlink /proc/$$/fd/1)'

Then simply call cd $(python -c ... | tee2tty)

This of course requires you to already know what you want to do with the output but has the advantage of calling the command only once.