Bash: Syntax error: redirection unexpected

Question

Does your script reference /bin/bash or /bin/sh in its hash bang line? The default system shell in Ubuntu is dash, not bash, so if you have #!/bin/sh then your script will be using a different shell than you expect. Dash does not have the <<< redirection operator.

Make sure the shebang line is:

#!/bin/bash

or

#!/usr/bin/env bash

And run the script with:

$ ./script.sh

Do not run it with an explicit sh as that will ignore the shebang:

$ sh ./script.sh   # Don't do this!

If you're using the following to run your script:

sudo sh ./script.sh

Then you'll want to use the following instead:

sudo bash ./script.sh

The reason for this is that Bash is not the default shell for Ubuntu. So, if you use "sh" then it will just use the default shell; which is actually Dash. This will happen regardless if you have #!/bin/bash at the top of your script. As a result, you will need to explicitly specify to use bash as shown above, and your script should run at expected.

Dash doesn't support redirects the same as Bash.

Docker:

I was getting this problem from my Dockerfile as I had:

RUN bash < <(curl -s -S -L https://raw.githubusercontent.com/moovweb/gvm/master/binscripts/gvm-installer)

However, according to this issue, it was solved:

The exec form makes it possible to avoid shell string munging, and to RUN commands using a base image that does not contain /bin/sh.

Note

To use a different shell, other than /bin/sh, use the exec form passing in the desired shell. For example,

RUN ["/bin/bash", "-c", "echo hello"]

---

Solution:

RUN ["/bin/bash", "-c", "bash < <(curl -s -S -L https://raw.githubusercontent.com/moovweb/gvm/master/binscripts/gvm-installer)"]

Notice the quotes around each parameter.

You can get the output of that command and put it in a variable. then use heredoc. for example:

nc -l -p 80 <<< "tested like a charm";

can be written like:

nc -l -p 80 <<EOF
tested like a charm
EOF

and like this (this is what you want):

text="tested like a charm"
nc -l -p 80 <<EOF
$text
EOF

Practical example in busybox under docker container:

kasra@ubuntu:~$ docker run --rm -it busybox
/ # nc -l -p 80 <<< "tested like a charm";
sh: syntax error: unexpected redirection


/ # nc -l -p 80 <<EOL
> tested like a charm
> EOL
^Cpunt!       => socket listening, no errors. ^Cpunt! is result of CTRL+C signal.


/ # text="tested like a charm"
/ # nc -l -p 80 <<EOF
> $text
> EOF
^Cpunt!

do it the simpler way,

direc=$(basename `pwd`)

Or use the shell

$ direc=${PWD##*/}