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Run a string as a command within a Bash script

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What is $() in bash script?

$() Command Substitution According to the official GNU Bash Reference manual: “Command substitution allows the output of a command to replace the command itself.

How do you run a variable in a shell script?

Here, the first line of the script i.e. “#!/bin/bash” shows that this file is in fact a Bash file. Then we have created a variable named “test” and have assigned it the value “$(echo “Hi there!”)”. Whenever you want to store the command in a variable, you have to type that command preceded by a “$” symbol.


You can use eval to execute a string:

eval $illcommando

your_command_string="..."
output=$(eval "$your_command_string")
echo "$output"

I usually place commands in parentheses $(commandStr), if that doesn't help I find bash debug mode great, run the script as bash -x script


don't put your commands in variables, just run it

matchdir="/home/joao/robocup/runner_workdir/matches/testmatch/"
PWD=$(pwd)
teamAComm="$PWD/a.sh"
teamBComm="$PWD/b.sh"
include="$PWD/server_official.conf"
serverbin='/usr/local/bin/rcssserver'    
cd $matchdir
$serverbin include=$include server::team_l_start = ${teamAComm} server::team_r_start=${teamBComm} CSVSaver::save='true' CSVSaver::filename = 'out.csv'

./me casts raise_dead()

I was looking for something like this, but I also needed to reuse the same string minus two parameters so I ended up with something like:

my_exe ()
{
    mysql -sN -e "select $1 from heat.stack where heat.stack.name=\"$2\";"
}

This is something I use to monitor openstack heat stack creation. In this case I expect two conditions, an action 'CREATE' and a status 'COMPLETE' on a stack named "Somestack"

To get those variables I can do something like:

ACTION=$(my_exe action Somestack)
STATUS=$(my_exe status Somestack)
if [[ "$ACTION" == "CREATE" ]] && [[ "$STATUS" == "COMPLETE" ]]
...