How can i store commands as a variables and execute them randomly in bash?

Question

How can i store commands as a variables and execute them randomly in bash?

command1="
   convert -size 2000x1000 xc:none -gravity center \
    -stroke yellow -pointsize 50 -font Courier-BoldOblique -strokewidth 3 -annotate +100+100 "${caption}" \
    -blur 0x25 -level 0%,50% \
    -fill white -stroke none -annotate +100+100 "${caption}" \
    in.jpeg  +swap -gravity center -geometry +0-3 \
    -composite  out.jpeg
"
command2="
   convert -size 2000x1000 xc:none -gravity center \
    -fill white -pointsize 50 -stroke none -annotate +100+100 "${caption}" -channel alpha -evaluate multiply 0.35 -trim +repage \
    in.jpeg  +swap -gravity center -geometry +0-3 \
    -composite  out.jpeg
"

What have i tried

COMMANDS=("command1" "command2")
$(eval $(shuf -n1 -e "${COMMANDS[@]}"))

Desired output is to randomly run any of the two convert commands. How can i get the desired result and where are the things going wrong ??

I have taken hints from -

execute-random-command

how-to-store-a-command-in-a-variable-in-a-shell-script

Thanks in advance for help !!

Answer 1

Use a function.

command1(){ 
   convert -size 2000x1000 xc:none -gravity center \
    -stroke yellow -pointsize 50 -font Courier-BoldOblique -strokewidth 3 -annotate +100+100 "${caption}" \
    -blur 0x25 -level 0%,50% \
    -fill white -stroke none -annotate +100+100 "${caption}" \
    in.jpeg  +swap -gravity center -geometry +0-3 \
    -composite  out.jpeg
}

command2() {
   convert -size 2000x1000 xc:none -gravity center \
    -fill white -pointsize 50 -stroke none -annotate +100+100 "${caption}" -channel alpha -evaluate multiply 0.35 -trim +repage \
    in.jpeg  +swap -gravity center -geometry +0-3 \
    -composite  out.jpeg
}

See why Why variables fail when trying to run a command

Answer 2

First, this won't work the moment you have whitespace or literal glob characters in the arguments:

command1="convert ... -fill white -stroke none -annotate +100+100 "${caption}" ...

Note how even the syntax highlighting shows that the ${caption} part is not quoted. Quotes don't work inside quotes, i.e. quotes expanded from a parameter are literal, they don't quote again.

See:

• How can we run a command stored in a variable?
• BashFAQ 050 - "I'm trying to put a command in a variable, but the complex cases always fail!"
• Why does my shell script choke on whitespace or other special characters?

Two better options are to store the commands in separate functions, or separate arrays. Sadly, you'll have to come with names for them, you can't have a (numbered) array of functions or an array of arrays.

Then, assuming you have functions or arrays called cmd1 and cmd2, choose one just like you did there, and if you used functions, just run it:

commands=(cmd1 cmd2)
chosen=$(shuf -n1 -e "${commands[@]}")
"$chosen" args...

or if you used an array, you'll have to use a name ref to access it:

commands=(cmd1 cmd2)
declare -n chosen=$(shuf -n1 -e "${commands[@]}")
"${chosen[@]}" args...