Access built-in shell commands like 'history' or 'fc'

Ruby
1

How do I access built-in shell commands (like ‘history’ or ‘fc’) with a
system call?

Not what I was expecting:
% ruby -e 'puts history’
-e:1: command not found: history

But this works fine:

% ruby -e 'puts pwd’
/home/john

I’ve tried this:

% ruby -e ‘system “history >tmp.tmp”; puts IO.read(“tmp.tmp”)’

And no errors are generated, but there is nothing in tmp.tmp, either.

Thanks

2

bwv549 wrote:

  /home/john

I’ve tried this:

% ruby -e ‘system “history >tmp.tmp”; puts IO.read(“tmp.tmp”)’

And no errors are generated, but there is nothing in tmp.tmp, either.

Thanks
Could it be that Ruby is using a different shell than you are used to?
I think it uses /bin/sh by default (not sure).

-Justin

3

On Thu, 10 Aug 2006, bwv549 wrote:

 /home/john

I’ve tried this:

% ruby -e ‘system “history >tmp.tmp”; puts IO.read(“tmp.tmp”)’

And no errors are generated, but there is nothing in tmp.tmp, either.

Thanks

system ‘sh -c history’

however there really won’t be one since the invocation of sh immediately
exits.

you may find my session lib helpful

require ‘session’ # gem install session

sh = Session::SH.new

stdout, stderr = sh.execute ‘ls’
p sh.status

stdout, stderr = sh.execute ‘history’ # this will have ‘ls’ in it!
p sh.status

regards.

-a

4

Could it be that Ruby is using a different shell than you are used to?
I think it uses /bin/sh by default (not sure).

Perhaps that is part of it. However, on this suggestion, I entered the
suggested shell (/bin/sh). However, the behavior hasn’t changed,
although the ‘history’ command works fine in this shell.

Just for reference, this is what I get when checking what this shell
is:

% /bin/sh --version
GNU bash, version 3.1.17(1)-release (i486-pc-linux-gnu)
Copyright © 2005 Free Software Foundation, Inc.

I’m on Ubuntu 6.X, just for reference.

Thanks

5

bwv549 wrote:

% /bin/sh --version
GNU bash, version 3.1.17(1)-release (i486-pc-linux-gnu)
Copyright © 2005 Free Software Foundation, Inc.

I’m on Ubuntu 6.X, just for reference.

Thanks
Yeah, that’s probably not it. Sorry.

-Justin

6

Why not access them by reading the file ~/.bash-history?

Regards, Morton

7

On Thu, 10 Aug 2006, Morton G. wrote:

% ruby -e 'puts pwd’
/home/john

I’ve tried this:

% ruby -e ‘system “history >tmp.tmp”; puts IO.read(“tmp.tmp”)’

And no errors are generated, but there is nothing in tmp.tmp, either.

that’s because each call starts a new shell so you won’t have any
history!

see my post about session.

-a

8

On 09.08.2006 21:51, bwv549 wrote:

% /bin/sh --version
GNU bash, version 3.1.17(1)-release (i486-pc-linux-gnu)
Copyright © 2005 Free Software Foundation, Inc.

I’m on Ubuntu 6.X, just for reference.

There is really no point in accessing the history of the shell because
what you likely want is the history of the invoking shell, i.e. the
one that started your ruby interpreter. AFAIK there is no way to access
that history. If you want to work with that you can do this at the
shell prompt.

history | ruby -e ‘…’

Your example with “pwd” worked because “pwd” is also an external program
(try it out with “type -a pwd”). But you can access PWD much easier
from inside Ruby:

12:03:59 [~]: ruby -e ‘puts Dir.pwd, ENV[“PWD”]’
/cygdrive/w
/cygdrive/w

Kind regards

robert
9

if HISTFILE is in rbconfig

  ruby -e 'IO.read(ENV["HISTFILE"]).split.each {|i| puts i}'

else

  ruby -e 'IO.read(ENV["HOME"] + "/.bash_history").split.each {|i|

puts i}’

10

On Wed, 09 Aug 2006 12:28:44 -0700, bwv549 wrote:

  /home/john

I’ve tried this:

% ruby -e ‘system “history >tmp.tmp”; puts IO.read(“tmp.tmp”)’

And no errors are generated, but there is nothing in tmp.tmp, either.

Thanks

I think under certain circumstances either ruby doesn’t call the shell
(and just calls the executable) or the shell doesn’t recognize builtin
commands when called as sh -c

For example:
irb(main):001:0> puts cd scratch
(irb):1: command not found: cd scratch

=> nil
irb(main):002:0> puts pwd
/home/bloom
=> nil
irb(main):003:0> puts type pwd
(irb):3: command not found: type pwd

=> nil
irb(main):004:0> puts type pwd && echo
pwd is a shell builtin

=> nil
irb(main):005:0> puts which pwd
/bin/pwd
=> nil

pwd works because it also happens to be a binary in /bin

–Ken B.

11

I think under certain circumstances either ruby doesn’t call the shell
(and just calls the executable) or the shell doesn’t recognize builtin
commands when called as sh -c

that’s it.
The most shells provide build-in commands only in the interactive mode.
Some shells coIMost shells print something like “can’t find…”, some
shells also print a littl help.

example (on zsh):

$ echo history | zsh
history: not interactive shell

regards,
Matthias