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

[bwv549]

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

 

[Justin Collins]

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

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

 

[ara.t.howard]

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

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

 

[bwv549]

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 (C) 2005 Free Software Foundation, Inc.

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

Thanks

 

[Morton Goldberg]

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

Regards, Morton

 

[ara.t.howard]

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

see my post about session.

-a

 

[Robert Klemme]

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 (C) 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

 

[x1]

# 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}'

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 (C) 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

 

[Ken Bloom]

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

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 Bloom

 

[Matthias Ludwig]

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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

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