#32 Directly get the first line of a shell command output into a variable

[astx]

Attached a POC for a new command: "setcmd variablename = shellcommand shellargs"
Directly get the first line of a shell commands output. Only a POC, untested, unchecked if secure, unchecked for memory leaks ... I'm not a c programmer ...
It would be nice if multiline results are supported too as array ...

An example console output:

ngspice 8427 -> shell cat t.pl
#!/usr/bin/perl
printf("%f\n", 5.38135e+006/1000000);

ngspice 8428 -> setcmd myvar=perl ./t.pl
setcmd: 1 <myvar=perl ./t.pl>
setcmd: 2 <myvar> <perl ./t.pl>
setcmd: 3 var=<myvar> result=<5.381350>

ngspice 8429 -> set
...
myvar 5.381350
...

BR, Toni

[marcel hendrix]

On 2019-02-07 17:08, astx wrote:

---

[patches:#32] Directly get the first line of a shell command output
into a variable

Status: open
Group: Unstable (example)
Labels: Patches
Created: Thu Feb 07, 2019 04:08 PM UTC by astx
Last Updated: Thu Feb 07, 2019 04:08 PM UTC
Owner: Holger Vogt
Attachments:

-
ngspice_poc_add_setcmd_command_to_directly_send_shell_output_to_variable.diff
(4.7 kB; text/x-patch)

Attached a POC for a new command: "setcmd variablename = shellcommand
shellargs"
Directly get the first line of a shell commands output. Only a POC,
untested, unchecked if secure, unchecked for memory leaks ... I'm not
a c programmer ...
It would be nice if multiline results are supported too as array ...

An example console output:
~~~
ngspice 8427 -> shell cat t.pl

!/usr/bin/perl

printf("%f\n", 5.38135e+006/1000000);

ngspice 8428 -> setcmd myvar=perl ./t.pl
setcmd: 1 <myvar=perl t.pl="" .="">
setcmd: 2 <myvar> <perl t.pl="" .="">
setcmd: 3 var=<myvar> result=<5.381350></myvar></perl></myvar></myvar=perl>

ngspice 8429 -> set
...
myvar 5.381350
...

~~~

Did you know this one:

ngspice 1 -> set a=`dc -e '3 4 * p'`
ngspice 2 -> echo $a
12
ngspice 3 ->

-marcel

[astx]

No - didn't know, that backticks are working partially. Couldn't find any hint in the manual. Sorry I haven't read it completely line by line - only searched for "backtick".
Fine that it's supported! For a single value it is usable, but - compared are the results here on string operation:

ngspice 8464 -> set myvar1=`/bin/bash -c "echo $curplottitle"`
ngspice 8465 -> setcmd myvar2=/bin/bash -c "echo $curplottitle"
setcmd: 1 <myvar2=/bin/bash -c "echo Constant values">
setcmd: 2 <myvar2> </bin/bash -c "echo Constant values">
setcmd: 3 var=<myvar2> result=<Constant values>
ngspice 8466 -> set
...
myvar1        Constant
myvar2        Constant values
...

BR, Toni

[astx]

Aaahhh: in the manual at 17.10 there is a hint for "backquote" - I searched for "backtick"
... the corresponding file is "src/frontend/parser/backq.c"

ngspice 8512 -> set myvar1=`/bin/bash -c "echo '( 1 2 3 4 5 )'"`
ngspice 8513 -> setcmd myvar2=/bin/bash -c "echo '( 1 2 3 4 5 )'"
setcmd: 1 <myvar2=/bin/bash -c "echo '( 1 2 3 4 5 )'">
setcmd: 2 <myvar2> </bin/bash -c "echo '( 1 2 3 4 5 )'">
setcmd: 3 var=<myvar2> result=<( 1 2 3 4 5 )>
ngspice 8514 -> set
...
myvar1        ( 1 2 3 4 5 )
myvar2        ( 1 2 3 4 5 )
...

Look same, but isn't (CP_LIST versus CP_STRING)
With backquotes the myvar1 is converted to an array, with poc "setcmd" the string stays untouched.

ngspice 8529 -> echo $myvar1[2]
2
ngspice 8530 -> echo $myvar2[2]

ngspice 8531 ->

String/array handling is very confusing ...
IMHO: if a program returns a string it should stay a string. To convert a string to an array a function should be used. E.g.: perl uses the "split" command to convert a string to an array.

Will take a closer look to the backquote/backtick feature.

BR, Toni