putting something into single quotes in a bash script

[Peter G.]

What is the difference in a bash script when one places something between 
single quotes:

- using the apostrophe, '
- using the accent grave, `

?

Eg.,

ps -fu 'whoami'
ps -fu `whoami`

They produce entirely different results.

There are many other places where one might wish to put a command, variable, 
etc., into single quotes, so, which type of single quote sahould be used and 
what is the diffence between the two?

[Michael Cronenworth]

Petrus de Calguarium wrote:
> ps -fu 'whoami'

This just passes the text whoami as a group argument with no execution 
of whoami.

ps -fu whoami
^
Equivalent command
> ps -fu `whoami`

The accent graves tell bash to execute the text inside them. The whoami 
command will be executed then passed to ps -fu.

[g]

On 02/02/2011 08:43 PM, Petrus de Calguarium wrote:
> What is the difference in a bash script when one places something between 
> single quotes:

single/double quotes and grave are something i tend to forget sometimes.

i find it quicker, easier and refreshing to run

man bash

the search on the work *quote*.

if i use then incorrectly enough, it will sink in and i will not have
to keep looking them up. :)

[Peter G.]

g wrote:
> man bash

The man page for bash is the worst one of all! I use man all the time for all 
kinds of commands, but anything to do with bash directs you to this bash page, 
meaning you have to pore over hundreds of separate entries in the vain hope of 
finding something relevant to your query.

[g]

On 02/03/2011 12:59 AM, Petrus de Calguarium wrote:
<>
> The man page for bash is the worst one of all!

not really. using '/' to look for what you want to know about makes it
very informative. at least for me. maybe not for some who are not used
to man pages.
> I use man all the time for all kinds of commands, but anything to
> do with bash directs you to this bash page,

actually, only 6;

sh(1), ksh(1), csh(1), emacs(1), vi(1), readline(3)

of which, 'sh(1)' kicks back to 'man bash'. while ksh(1) and csh(1) do
have one hell of a lot more 'see also'.

first 4 'see also' are manuals and references for readings outside of man.
> meaning you have to pore over hundreds of separate entries in the
> vain hope of finding something relevant to your query.

only if i do not comprehend what i am reading in said man page.

[Peter G.]

g wrote:
> maybe not for some who are not used
> to man pages.

Actually, I am intimately familiar with man pages; however, the only commands I 
know are space bar, 'b', 'q' and the mouse wheel.

[Joe Zeff]

On 02/03/2011 10:49 AM, Petrus de Calguarium wrote:
> Actually, I am intimately familiar with man pages; however, the only commands I
> know are space bar, 'b', 'q' and the mouse wheel.

Man uses less for display.  To learn more about it, use

man less

[g]

On 02/03/2011 07:41 PM, Joe Zeff wrote:
<>
> Man uses less for display.  To learn more about it, use

this is true. but then he would have to have 2 terminal windows open until
he learns more commands. ;)

after which, he can learn 'info', as poc suggested, and then he will have
a whole new command group to learn. :)

btw. pressing <h> in 'info' gives help information also.
> man less

gives more command information than what is used in 'man'.

[g]

On 02/03/2011 06:49 PM, Petrus de Calguarium wrote:
<>
> Actually, I am intimately familiar with man pages; however, the only
> commands I know are space bar, 'b', 'q' and the mouse wheel.

then you need to become more intimate with 'man'.

run;

man man

while there, press <h> key.

may you intimacy become a joy. :)

[Patrick O'Callaghan]

On Wed, 2011-02-02 at 17:59 -0700, Petrus de Calguarium wrote:
> g wrote:
> > man bash
>
> The man page for bash is the worst one of all! I use man all the time for all 
> kinds of commands, but anything to do with bash directs you to this bash page, 
> meaning you have to pore over hundreds of separate entries in the vain hope of 
> finding something relevant to your query.

info bash

poc

[John Wendel]

On 02/02/2011 07:09 PM, Patrick O'Callaghan wrote:
> On Wed, 2011-02-02 at 17:59 -0700, Petrus de Calguarium wrote:
> > g wrote:
> > > man bash
> >
> > The man page for bash is the worst one of all! I use man all the time for all
> > kinds of commands, but anything to do with bash directs you to this bash page,
> > meaning you have to pore over hundreds of separate entries in the vain hope of
> > finding something relevant to your query.
>
> info bash
>
> poc

See the Advanced Bash Scripting Guide at

tldp.org/LDP/abs/html/

Regards

John

[Patrick O'Callaghan]

On Wed, 2011-02-02 at 13:43 -0700, Petrus de Calguarium wrote:
> What is the difference in a bash script when one places something between 
> single quotes:
> using the apostrophe, '
> using the accent grave, `
>
> ?
>
> Eg.,
>
> ps -fu 'whoami'
> ps -fu `whoami`
>
> They produce entirely different results.

Of course they do. They are entirely different things. The first one is
for quoting strings which might contain Shell metacharacters. The second
is to execute a command and insert its output as the value of the
string, e.g.

ls -l `find ~/.kde`

This is equivalent to:

ls -l $(find ~/.kde)

but the latter is a more recent form (it has the advantage of being
nestable, which the older form isn't).

And then there's the difference between " and ' ...

I recommend reading up on bash to fully understand this last part. It's
not trivial to explain.

poc

[g]

On 02/02/2011 09:32 PM, Patrick O'Callaghan wrote:
<>
> I recommend reading up on bash to fully understand this last part. It's
> not trivial to explain.

or to understand.

[Joe Zeff]

On 02/02/2011 01:32 PM, Patrick O'Callaghan wrote:
> I recommend reading up on bash to fully understand this last part. It's
> not trivial to explain.

You might find what you need at http://tldp.org/LDP/abs/html/

[Peter G.]

Joe Zeff wrote:
> You might find what you need at http://tldp.org/LDP/abs/html/

Thanks for the suggestion, but I don't have the time to read a book just to 
find out the meaning of ` and learn that it is not the same as '.

[Suvayu Ali]

On Wed, Feb 2, 2011 at 4:57 PM, Petrus de Calguarium  wrote:
> Joe Zeff wrote:
> > You might find what you need at http://tldp.org/LDP/abs/html/
>
> Thanks for the suggestion, but I don't have the time to read a book just to
> find out the meaning of ` and learn that it is not the same as '.

Learning to use the shell effectively requires a bit of patience. Let
me make it a little easier for you,

http://tldp.org/LDP/abs/html/quoting.html
http://tldp.org/LDP/abs/html/varsubn.html
http://tldp.org/LDP/abs/html/commandsub.html

HTH

[g]

On 02/02/2011 10:55 PM, Joe Zeff wrote:
> On 02/02/2011 01:32 PM, Patrick O'Callaghan wrote:
> > I recommend reading up on bash to fully understand this last part. It's
> > not trivial to explain.
>
> You might find what you need at http://tldp.org/LDP/abs/html/

i believe poc was just stating that 'recent form' requires more explaining
than what he did in simplifying 'grave'. is, 'rtfmp'.

i do agree with you about 'tldp' having plenty of information. they do
live up to their name.

[Peter G.]

Patrick O'Callaghan wrote:
> Of course they do. They are entirely different things. The first one is
> for quoting strings which might contain Shell metacharacters. The second
> is to execute a command and insert its output as the value of the
> string, e.g.
>
> ls -l `find ~/.kde`
>
> This is equivalent to:
>
> ls -l $(find ~/.kde)
>
> but the latter is a more recent form (it has the advantage of being
> nestable, which the older form isn't).

Thank you. That explains it well.

I will read up a bit, too.