• Uncategorized

About bash : Bash-Syntax-error-redirection-unexpected

Question Detail

I do this in a script:

read direc <<< $(basename `pwd`)

and I get:

Syntax error: redirection unexpected

in an ubuntu machine

/bin/bash --version
GNU bash, version 4.0.33(1)-release (x86_64-pc-linux-gnu)

while I do not get this error in another suse machine:

/bin/bash --version
GNU bash, version 3.2.39(1)-release (x86_64-suse-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.

Why the error?

Question Answer

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:

[email protected]:~$ 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##*/}

Another reason to the error may be if you are running a cron job that updates a subversion working copy and then has attempted to run a versioned script that was in a conflicted state after the update…

On my machine, if I run a script directly, the default is bash.

If I run it with sudo, the default is sh.

That’s why I was hitting this problem when I used sudo.

In my case error is because i have put “>>” twice

mongodump --db=$DB_NAME --collection=$col --out=$BACKUP_LOCATION/$DB_NAME-$BACKUP_DATE >> >> $LOG_PATH

i just correct it as

mongodump --db=$DB_NAME --collection=$col --out=$BACKUP_LOCATION/$DB_NAME-$BACKUP_DATE >> $LOG_PATH

Before running the script, you should check first line of the shell script for the interpreter.

Eg:
if scripts starts with /bin/bash , run the script using the below command
“bash script_name.sh”

if script starts with /bin/sh, run the script using the below command
“sh script_name.sh”

./sample.sh – This will detect the interpreter from the first line of the script and run.

Different Linux distributions having different shells as default.

You may also like...

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.