Run a string as a command within a Bash script

Question

I have a Bash script that builds a string to run as a command

Script:

#! /bin/bash

matchdir="/home/joao/robocup/runner_workdir/matches/testmatch/"

teamAComm="`pwd`/a.sh"
teamBComm="`pwd`/b.sh"
include="`pwd`/server_official.conf"
serverbin='/usr/local/bin/rcssserver'

cd $matchdir
illcommando="$serverbin include='$include' server::team_l_start = '${teamAComm}' server::team_r_start = '${teamBComm}' CSVSaver::save='true' CSVSaver::filename = 'out.csv'"

echo "running: $illcommando"
# $illcommando > server-output.log 2> server-error.log
$illcommando

which does not seem to supply the arguments correctly to the $serverbin.

Script output:

running: /usr/local/bin/rcssserver include='/home/joao/robocup/runner_workdir/server_official.conf' server::team_l_start = '/home/joao/robocup/runner_workdir/a.sh' server::team_r_start = '/home/joao/robocup/runner_workdir/b.sh' CSVSaver::save='true' CSVSaver::filename = 'out.csv'
rcssserver-14.0.1

Copyright (C) 1995, 1996, 1997, 1998, 1999 Electrotechnical Laboratory.
2000 - 2009 RoboCup Soccer Simulator Maintenance Group.


Usage: /usr/local/bin/rcssserver [[-[-]]namespace::option=value]
                                 [[-[-]][namespace::]help]
                                 [[-[-]]include=file]
Options:
    help
        display generic help

    include=file
        parse the specified configuration file.  Configuration files
        have the same format as the command line options. The
        configuration file specified will be parsed before all
        subsequent options.

    server::help
        display detailed help for the "server" module

    player::help
        display detailed help for the "player" module

    CSVSaver::help
        display detailed help for the "CSVSaver" module

CSVSaver Options:
    CSVSaver::save=<on|off|true|false|1|0|>
        If save is on/true, then the saver will attempt to save the
        results to the database.  Otherwise it will do nothing.

        current value: false

    CSVSaver::filename='<STRING>'
        The file to save the results to.  If this file does not
        exist it will be created.  If the file does exist, the results
        will be appended to the end.

        current value: 'out.csv'

if I just paste the command /usr/local/bin/rcssserver include='/home/joao/robocup/runner_workdir/server_official.conf' server::team_l_start = '/home/joao/robocup/runner_workdir/a.sh' server::team_r_start = '/home/joao/robocup/runner_workdir/b.sh' CSVSaver::save='true' CSVSaver::filename = 'out.csv' (in the output after "runnning: ") it works fine.

Note that in some cases, you need to do: echo | whateverCommands instead of just whateverCommands (for instance, I had to do it like this: | tail -`echo | whateverCommands`) — Andrew
– Andrew, Commented Sep 13, 2017 at 21:45

jave.web · Accepted Answer · 2023-09-18 12:48:42Z

362

You can use eval to execute a string:

eval $illcommando

If your command string needs to be evaluated itself before it is ran - wrap in quotes:

eval "$yourcommand"
# e.g. eval "command argument  --your-option='$(date -d "$date" +%Y-%m-%d)'"

edited Sep 18, 2023 at 12:48

jave.web

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answered Mar 1, 2010 at 10:52

Arne Burmeister

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7 Comments

Tomáš Zato Over a year ago

Does eval pass forward the command return value (return value, not string output)?

Krishnadas PC Over a year ago

eval is an evil command in all programming languages so use it with caution.

Charles Duffy Over a year ago

eval "$illcommando", with the quotes, to not have your command mangled before it's run. Try evaling with a value of illcommando='printf "%s\n" " * "' with and without the quotes to see the difference.

Cameron Hudson Over a year ago

@TomášZato-ReinstateMonica Yes, it does forward the return value of the command. However, it does NOT set the "${PIPESTATUS[@]}" variable in bash properly. However, set -o pipefail does properly cause eval to return a failure exit code if the command contains failing command piped to a successful command.

tripleee Over a year ago

Solutions suggesting eval should always discuss the security implications. unix.stackexchange.com/questions/23111/… See also When to wrap quotes around a shell variable

|

Takman · Accepted Answer · 2018-06-02 00:42:03Z

35

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

answered Jun 2, 2018 at 0:42

Takman

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3 Comments

kklepper Over a year ago

Looks interesting, but does not work for me. $your_command_string does not get executed. What is the problem?

Cadoiz Over a year ago

Worked for me. Don't know where to put it, but pay attention, that you don't put a space before the = like your_command_string ="..."

tripleee Over a year ago

This merely decorates the accepted answer from 2010 with a useless echo

Ola · Accepted Answer · 2010-03-01 10:39:36Z

29

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

answered Mar 1, 2010 at 10:39

Ola

4853 silver badges4 bronze badges

4 Comments

Robin Manoli Over a year ago

I'm not sure what commandStr refers to, but at least this didn't work for me. It's better if you use full working examples.

Andrew Over a year ago

@RobinManoli Improved the clarity for ya.

Osman Over a year ago

commandStr="ls -l" $(echo commandStr) #should work

Ed Swangren Over a year ago

@Osman "Should work" meaning "will work so long as your input contains nothing that would cause unexpected results when subjected to expansions and word splitting". It doesn't work so well without quotes"$(echo commandStr)".

ghostdog74 · Accepted Answer · 2010-03-01 10:50:59Z

12

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'

answered Mar 1, 2010 at 10:50

ghostdog74

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3 Comments

João Portela Over a year ago

did just that. but where I had variables that should go just as a single argument i did "${arg}". example: server::team_l_start = "${teamAComm}"

Zane Over a year ago

For a lot of debugging tasks, it is a good idea to have the command in a string. Saves me a lot of headaches.

tripleee Over a year ago

There are also a lot of situations where having your command in a string brings on a new and stronger kind of headache. Probably review mywiki.wooledge.org/BashFAQ/050

cmyster · Accepted Answer · 2016-07-17 06:31:14Z

3

./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" ]]
...

answered Jul 17, 2016 at 6:31

cmyster

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Comments

KANJICODER · Accepted Answer · 2019-05-23 18:27:20Z

Here is my gradle build script that executes strings stored in heredocs:

current_directory=$( realpath "." )
GENERATED=${current_directory}/"GENERATED"
build_gradle=$( realpath build.gradle )

## touch because .gitignore ignores this folder:
touch $GENERATED

COPY_BUILD_FILE=$( cat <<COPY_BUILD_FILE_HEREDOC

    cp 
        $build_gradle 
        $GENERATED/build.gradle

COPY_BUILD_FILE_HEREDOC
)
$COPY_BUILD_FILE

GRADLE_COMMAND=$( cat <<GRADLE_COMMAND_HEREDOC

    gradle run

        --build-file       
            $GENERATED/build.gradle

        --gradle-user-home 
            $GENERATED  

        --no-daemon

GRADLE_COMMAND_HEREDOC
)
$GRADLE_COMMAND

The lone ")" are kind of ugly. But I have no clue how to fix that asthetic aspect.

Egal · Accepted Answer · 2020-07-15 09:40:31Z

0

To see all commands that are being executed by the script, add the -x flag to your shabang line, and execute the command normally:

#! /bin/bash -x

matchdir="/home/joao/robocup/runner_workdir/matches/testmatch/"

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'

Then if you sometimes want to ignore the debug output, redirect stderr somewhere.

answered Jul 15, 2020 at 9:40

Egal

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Comments

Mayur Gite · Accepted Answer · 2020-08-25 13:57:23Z

0

For me echo XYZ_20200824.zip | grep -Eo '[[:digit:]]{4}[[:digit:]]{2}[[:digit:]]{2}' was working fine but unable to store output of command into variable. I had same issue I tried eval but didn't got output.

Here is answer for my problem: cmd=$(echo XYZ_20200824.zip | grep -Eo '[[:digit:]]{4}[[:digit:]]{2}[[:digit:]]{2}')

echo $cmd

My output is now 20200824

answered Aug 25, 2020 at 13:57

Mayur Gite

3944 silver badges18 bronze badges

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