How to execute the output of `ls` from the command line?

Question

Sometimes I forget my relative paths and by the time I track down where the file, is I have typed :

Cris-Mac-Book-2:weird cris$ ls ../../../
Icon?       Research    Support
Cris-Mac-Book-2:weird cris$ ls ../../../Support
Fourganizical       PicoCryptical       SupportPlan.txt
MoneyProjectical    Qwontical       Testcomms
OSICAL          StanTechStatistical todo
Cris-Mac-Book-2:weird cris$ ls ../../../Support/PicoCryptical
S   cs  mini    php py  readme
Cris-Mac-Book-2:weird cris$ ls ../../../Support/PicoCryptical/py/StanTechPico.py

To now run this script, I find myself pressing ← until I get back to the start of the command, then replacing python with ls.

When I do this long-hold ← (which seems to be often) I am always thinking, there must be a faster way to edit the command string, or execute the previous command's output.

So, not really qualifying as a bash superuser, I tried to pipe the output of ls to python, which didn't work as intended :

Cris-Mac-Book-2:weird cris$ ls ../../../Support/PicoCryptical/py/StanTechPico.py | python
  File "<stdin>", line 1
    ../../../Support/PicoCryptical/py/StanTechPico.py
    ^
SyntaxError: invalid syntax
Cris-Mac-Book-2:weird cris$

So my question : how to put the STDOUT output of a previous command, in the argument position of a new command?

Answer 1

^ls^python will perform your immediate need (repeat previous command, substituting python for the ls)

Answer 2

I'm not certain you're actually asking

But I guess what I really want is to know how to put the STDOUT output of one command in the argument position of another command, from the command line?

I think what you might find useful is using $_

$ ls /tmp/long/path/which/contains/file
/tmp/long/path/which/contains/file
$ python $_

The $_ is replaced with the final argument of the previous command you executed.

See http://tldp.org/LDP/abs/html/internalvariables.html

However, if you really do want to use the stdout as an argument for another command, you can use xargs for that (see http://linux.die.net/man/1/xargs)

$ ls /tmp/long/path/which/contains/file | xargs python

Answer 3

Have you ever used backticks?

python `ls ../../../somefile`

Will call python with the output of ls as its argument.

Not totally sure if that is what you are asking, though.

Answer 4

You can type

python

and press ALT + .

Pressing ALT + . inserts last argument of the last command. Pressing the shortcut again goes further backwards.

EDIT: I have tested this on different Linux and OpenBSD using bash,sh,ksh,dash,zsh. It does not seams work in (t)csh. Which surprises me because I thought its a feature of readline?!

Answer 5

Other than Andrew's answer, a good trick to know is that Ctrl+a jumps the cursor to the start of the line.

Answer 6

Your immediate need seems solved, but here are some solutions for your long term need of finding "a faster way to edit the command string".

From your example, it looks like you already have bash completion (http://www.hypexr.org/bash_tutorial.php#completion) on your system, so you should be able to do the exact same thing with Tab, just start the command with python instead of ls then Tab away.

Here are some of the basic shortcuts I find myself using all the time (most work on any *nix based system, but some ... especially OS X ... can be cranky sometimes).

• Ctrl + ← or Ctrl + → jumps by "words" instead of individual characters.
• Ctrl + A jumps to the beginning of the command line
• Ctrl + E jumps to the end of the command line

• !! will repeat the last command in the history (and print out what the command was)

  $ ls
file1
file2
$ !!
ls
file1
file2
  

• !$ will print the very last argument from your previous command ($_ is mentioned above, which is bash specific, is basically the equivalent ... there, I've done it, let the debate begin)

  $ ls ../file.py
file.py
$ python !$
python ../file.py
script output ...
  

For a few more great ones, see the "Keyboard Shortcuts" section on Linux Terminal Command Reference. Even though that page is specific to Linux Mint, the only *nix system I find unhappy with those shortcuts is OS X.