bash : Bad Substitution

The default shell (/bin/sh) under Ubuntu points to dash, not bash.

me@pc:~$ readlink -f $(which sh)
/bin/dash

So if you chmod +x your_script_file.sh and then run it with ./your_script_file.sh, or if you run it with bash your_script_file.sh, it should work fine.

Running it with sh your_script_file.sh will not work because the hashbang line will be ignored and the script will be interpreted by dash, which does not support that string substitution syntax.

I had the same problem. Make sure your script didnt have

#!/bin/sh 

at the top of your script. Instead, you should add

#!/bin/bash

For others that arrive here, this exact message will also appear when using the env variable syntax for commands, for example ${which sh} instead of the correct $(which sh)

Your script syntax is valid bash and good.

Possible causes for the failure:

Your bash is not really bash but ksh or some other shell which doesn't understand bash's parameter substitution. Because your script looks fine and works with bash. Do ls -l /bin/bash and check it's really bash and not sym-linked to some other shell. If you do have bash on your system, then you may be executing your script the wrong way like: ksh script.sh or sh script.sh (and your default shell is not bash). Since you have proper shebang, if you have bash ./script.sh or bash ./script.sh should be fine.

Try running the script explicitly using bash command rather than just executing it as executable.

Also, make sure you don't have an empty string for the first line of your script.

i.e. make sure #!/bin/bash is the very first line of your script.

Not relevant to your example, but you can also get the Bad substitution error in Bash for any substitution syntax that Bash does not recognize. This could be:

Stray whitespace. E.g. bash -c '${x }'

A typo. E.g. bash -c '${x;-}'

A feature that was added in a later Bash version. E.g. bash -c '${x@Q}' before Bash 4.4.

If you have multiple substitutions in the same expression, Bash may not be very helpful in pinpointing the problematic expression. E.g.:

$ bash -c '"${x } multiline string
$y"'
bash: line 1: ${x } multiline string
$y: bad substitution

Both - bash or dash - work, but the syntax needs to be:

FILENAME=/my/complex/path/name.ext
NEWNAME=${FILENAME%ext}new

I was adding a dollar sign twice in an expression with curly braces in bash:

cp -r $PROJECT_NAME ${$PROJECT_NAME}2

instead of

cp -r $PROJECT_NAME ${PROJECT_NAME}2

I have found that this issue is either caused by the marked answer or you have a line or space before the bash declaration

Looks like "+x" causes problems:

root@raspi1:~# cat > /tmp/btest
#!/bin/bash

jobname="job_201312161447_0003"
jobname_pre=${jobname:0:16}
jobname_post=${jobname:17}
root@raspi1:~# chmod +x /tmp/btest
root@raspi1:~# /tmp/btest
root@raspi1:~# sh -x /tmp/btest
+ jobname=job_201312161447_0003
/tmp/btest: 4: /tmp/btest: Bad substitution

in my case (under ubuntu 18.04), I have mixed $( ${} ) that works fine:

BACKUPED_NB=$(ls ${HOST_BACKUP_DIR}*${CONTAINER_NAME}.backup.sql.gz | wc --lines)

full example here.

I used #!bin/bash as well tried all approaches like no line before or after #!bin/bash.
Then also tried using +x but still didn't work. Finally i tried running the script ./script.sh it worked fine.

#!/bin/bash
jobname="job_201312161447_0003"
jobname_post=${jobname:17}

root@ip-10-2-250-36:/home/bitnami/python-module/workflow_scripts# sh jaru.sh jaru.sh: 3: jaru.sh: Bad substitution

root@ip-10-2-250-36:/home/bitnami/python-module/workflow_scripts# ./jaru.sh root@ip-10-2-250-36:/home/bitnami/python-module/workflow_scripts#