Shell Programming and Scripting

Hi,
i made a gnuplot script which accepts a filename as parameter (using gnuplot -e) now i want to run this script from a shell script, the correct command (with a concrete parameter) looks like this:

Code:

gnuplot -e 'name="filename.dat;col=2"' gplscript.gpl

my shell script looks like this:

Code:

        gnuplot -e \'name=\"${1}.dat\"\;col=2\' gplscript.gpl

        echo \'name=\"${1}.dat\"\;col=2\'

the output typing sh script.sh filename is:

Code:

'name="filename.dat";col=2'
^
line 0: invalid command

'name="filename.dat";col=2'

i must have made a mistake with the escaping but i cannot find it.

btw. the echo results is correct, as you can see it is the same as in the correct command example in the beginning and it works as it should.

But i use the same escape sequence in the gnuplot part of the shellscript which looks correct in the output, apart from the error.

By escaping the single quote, you've turned them into literal quote characters which get passed into gnuplot raw.

Code:

'name="filename.dat";col=2'

If you actually typed that into gnuplot quotes and all like that, it wouldn't work.

Since you want to expand variables inside the quotes, I suggest double quotes instead of single ones, unescaped. You can use single quotes inside without escaping them. Much less work.

Code:

gnuplot -e "name='${1}.dat';col=2" gplscript.gpl

thank you i will try this tomorrow when i have access to my workstation again.
but to make this clear, i need the single quotes in the gnuplot command because the flag -e expects a list of "commands" seperated by ";" within quotes (' ')
but i think the double quotes could work too.
btw: the example in the first quote block i posted above works fine

---------- Post updated 10-25-12 at 08:17 AM ---------- Previous update was 10-24-12 at 05:11 PM ----------

hi again, i just tested your suggestion and it works great, thanks again.

You've missed the point, not to mention seem confused about how quoting works.

The quotes are for the shell, not gnuplot. They tell a string not to split. GNUplot doesn't care about them. GNUplot doesn't see them, and shouldn't see them.

Code:

# quotes are not echoed.  The shell removes them before echo is run.
$ echo 'asdf'

asdf

# quotes are not echoed.  The shell removes them before echo is run.
$ echo "asdf"

asdf

$

If you're feeling masochistic, you can do this completely without quotes just by escaping everything:

Code:

gnuplot -e name=\'${1}.dat\'\;col=2 gplscript.gpl

...and gnuplot will swallow it happily as long as $1 contains no spaces. GNUplot doesn't care. It gets the exact same string once the shell's through with it.

Thank you for this helpful explanation, you are right i did not realy knew what the real purpose of those quotes is.