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A dash to GOTO or a dash from GOTO, that is the question...


 
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# 1  
A dash to GOTO or a dash from GOTO, that is the question...

Well, guys I saw a question about GOTO for Python.

So this gave me the inspiration to attempt a GOTO function for 'dash', (bash and ksh too).

Machine: MBP OSX 10.14.3, default bash terminal, calling '#!/usr/local/bin/dash'...

This is purely a fun project to see if it is possible in PURE shell scripting, and so it is...

I now consider myself competent at UNIX shell scripting...

Enjoy ripping it apart:

Code:
#!/usr/local/bin/dash
# goto_demo.sh

# goto ': some_label:'
goto()
{
    line_number=1
    start_line=1
    while IFS='' read -r line
    do
        if [ "${line}" = "${1}" ]
        then
            : > /tmp/goto.tmp
            start_line=${line_number}
        fi
        if [ ${line_number} -ge ${start_line} ]
        then
            echo "${line}" >> /tmp/goto.tmp
        fi
        line_number=$(( line_number + 1 ))
    done
    . /tmp/goto.tmp
} < ${0}

goto ': second:'
echo 'This will not be printed!'
: first:
echo '**************************************'
echo 'You are at first label!'
# cat /tmp/goto.tmp
echo '**************************************'
goto ': third:'
echo 'This will not be printed either!'
: second:
echo '**************************************'
echo 'You are at the second label!'
# cat /tmp/goto.tmp
echo '**************************************'
goto ': first:'
echo 'And finally, this will not be printed either!'
: third:
echo '**************************************'
echo 'You are at the third label!'
echo '######## cat /tmp/goto.tmp... ########'
cat /tmp/goto.tmp
echo '###### END cat /tmp/goto.tmp... ######'
echo '**************************************'
: end:
echo 'Exiting...'
echo '**************************************'
exit

Results using above:
Code:
Last login: Wed Sep 18 15:55:17 on ttys000
AMIGA:amiga~> cd Desktop/Code/Shell
AMIGA:amiga~/Desktop/Code/Shell> ./goto_demo.sh
**************************************
You are at the second label!
**************************************
**************************************
You are at first label!
**************************************
**************************************
You are at the third label!
######## cat /tmp/goto.tmp... ########
: third:
echo '**************************************'
echo 'You are at the third label!'
echo '######## cat /tmp/goto.tmp... ########'
cat /tmp/goto.tmp
echo '###### END cat /tmp/goto.tmp... ######'
echo '**************************************'
: end:
echo 'Exiting...'
echo '**************************************'
exit
###### END cat /tmp/goto.tmp... ######
**************************************
Exiting...
**************************************
AMIGA:amiga~/Desktop/Code/Shell> _

EDIT:
Tested on current Linux Mint 19, using the shebang #!/bin/sh and working as per the image.
A dash to GOTO or a dash from GOTO, that is the question...-goto_demopng

Last edited by wisecracker; 09-19-2019 at 10:42 AM..
These 2 Users Gave Thanks to wisecracker For This Post:
# 2  
Isn't line_number always equal to or greater than start_line?
It works because the output file is truncated at the right moment.

I would rather go for
Code:
goto()
{
    line_copy=
    while IFS='' read -r line
    do
        [ "$line" = "$1" ] && line_copy=1
        [ -n "$line_copy" ] && echo "$line"
    done < "$0" > /tmp/goto.tmp
    . /tmp/goto.tmp
}

Eventually swap the two lines in the loop, to omit the first line (then you do not need to prefix the lable with a nop).

Of course this is a hack. A function puts something on the "return" stack...
This User Gave Thanks to MadeInGermany For This Post:
# 3  
Quote:
Originally Posted by MadeInGermany
Isn't line_number always equal to or greater than start_line?
It works because the output file is truncated at the right moment.

I would rather go for
Code:
goto()
{
    line_copy=
    while IFS='' read -r line
    do
        [ "$line" = "$1" ] && line_copy=1
        [ -n "$line_copy" ] && echo "$line"
    done < "$0" > /tmp/goto.tmp
    . /tmp/goto.tmp
}

Eventually swap the two lines in the loop, to omit the first line (then you do not need to prefix the lable with a nop).

Of course this is a hack. A function puts something on the "return" stack...
I will replace my version with your function and give it a whirl.
I had in fact thought about using #some_label: as both methods would not create an error, something like command not found under normal running but I see your point.
And of course it's a hack, as I always quote "if there is a back door I will find it" and hacks by their nature are back doors....
# 4  
Hi MadeInGermany...
(Hopefully this does not attach to the previous post.)

Copied and pasted your segment into my original code and it works well.

Thanks...

Bazza...

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