Is there a “goto” statement in bash?

Question

Is there a "goto" statement in bash ? I know It is considered bad practice, but I need specifically "goto".

Answer 1

I found out a way to do this using functions.

Say, for example, you have 3 choices: A, B, and C. A and Bexecute a command, but C gives you more info and takes you to the original prompt again. This can be done using functions.

Note that since the line containg function demoFunction is just setting up the function, you need to call demoFunction after that script so the function will actually run.

You can easily adapt this by writing multiple other functions and calling them if you need to "GOTO" another place in your shell script.

function demoFunction {
        read -n1 -p "Pick a letter to run a command [A, B, or C for more info] " runCommand

        case $runCommand in
            a|A) printf "\n\tpwd being executed...\n" && pwd;;
            b|B) printf "\n\tls being executed...\n" && ls;;
            c|C) printf "\n\toption A runs pwd, option B runs ls\n" && demoFunction;;
        esac
}

demoFunction

Answer 2

There is no goto in bash.

Here is some dirty workaround using trap which jumps only backwards:)

#!/bin/bash -e
trap '
echo I am
sleep 1
echo here now.
' EXIT

echo foo
goto trap 2> /dev/null
echo bar

Output:

$ ./test.sh 
foo
I am
here now.

This shouldn't be used in that way, but only for educational purposes. Here is why this works:

trap is using exception handling to achieve the change in code flow. In this case the trap is catching anything that causes the script to EXIT. The command goto doesn't exist, and hence throws an error, which would ordinarily exit the script. This error is being caught with trap, and the 2>/dev/null hides the error message that would ordinarily be displayed.

This implementation of goto is obviously not reliable, since any non-existent command (or any other error, for that manner), would execute the same trap command. In particular, you cannot choose which label to go-to.

---

Basically in real scenario you don't need any goto statements, they're redundant as random calls to different places only make your code difficult to understand.

If your code is invoked many times, then consider to use loop and changing its workflow to use continue and break.

If your code repeats it-self, consider writing the function and calling it as many times as you want.

If your code needs to jump into specific section based on the variable value, then consider using case statement.

If you can separate your long code into smaller pieces, consider moving it into separate files and call them from the parent script.

Answer 3

This is a small correction of the Judy Schmidt script put up by Hubbbitus.

Putting non-escaped labels in the script was problematic on the machine and caused it to crash. This was easy enough to resolve by adding # to escape the labels. Thanks to Alexej Magura and access_granted for their suggestions.

#!/bin/bash
# include this boilerplate
function goto {  
label=$1
cmd=$(sed -n "/$#label#:/{:a;n;p;ba};" $0 | grep -v ':$')
eval "$cmd"
exit
}

start=${1:-"start"}

goto $start

#start#
echo "start"
goto bing

#boom#
echo boom
goto eof

#bang#
echo bang
goto boom

#bing#
echo bing
goto bang

#eof#
echo "the end mother-hugger..."

Answer 4

You can use case in bash to simulate a goto:

#!/bin/bash

case bar in
  foo)
    echo foo
    ;&

  bar)
    echo bar
    ;&

  *)
    echo star
    ;;
esac

produces:

bar
star

Answer 5

If you're testing/debugging a bash script, and simply want to skip forwards past one or more sections of code, here is a very simple way to do it that is also very easy to find and remove later (unlike most of the methods described above).

#!/bin/bash

echo "Run this"

cat >/dev/null <<GOTO_1

echo "Don't run this"

GOTO_1

echo "Also run this"

cat >/dev/null <<GOTO_2

echo "Don't run this either"

GOTO_2

echo "Yet more code I want to run"

To put your script back to normal, just delete any lines with GOTO.

We can also prettify this solution, by adding a goto command as an alias:

#!/bin/bash

shopt -s expand_aliases
alias goto="cat >/dev/null <<"

goto GOTO_1

echo "Don't run this"

GOTO_1

echo "Run this"

goto GOTO_2

echo "Don't run this either"

GOTO_2

echo "All done"

Aliases don't usually work in bash scripts, so we need the shopt command to fix that.

If you want to be able to enable/disable your goto's, we need a little bit more:

#!/bin/bash

shopt -s expand_aliases
if [ -n "$DEBUG" ] ; then
  alias goto="cat >/dev/null <<"
else
  alias goto=":"
fi

goto '#GOTO_1'

echo "Don't run this"

#GOTO1

echo "Run this"

goto '#GOTO_2'

echo "Don't run this either"

#GOTO_2

echo "All done"

Then you can do export DEBUG=TRUE before running the script.

The labels are comments, so won't cause syntax errors if disable our goto's (by setting goto to the ':' no-op), but this means we need to quote them in our goto statements.

Whenever using any kind of goto solution, you need to be careful that the code you're jumping past doesn't set any variables that you rely on later - you may need to move those definitions to the top of your script, or just above one of your goto statements.

Answer 6

If you are using it to skip part of a large script for debugging (see Karl Nicoll's comment), then if false could be a good option (not sure if "false" is always available, for me it is in /bin/false):

# ... Code I want to run here ...

if false; then

# ... Code I want to skip here ...

fi

# ... I want to resume here ...

The difficulty comes in when it's time to rip out your debugging code. The "if false" construct is pretty straightforward and memorable, but how do you find the matching fi? If your editor allows you to block indent, you could indent the skipped block (then you'll want to put it back when you're done). Or a comment on the fi line, but it would have to be something you'll remember, which I suspect will be very programmer-dependent.