While executing the below command directly over the terminal, its working fine:

comm -2 -3 <(sort FileOne.txt) <(sort FileTwo.txt) > myFile.txt

But while trying to execute it via .sh file, its giving error: Syntax error: "(" unexpected

Here is my code:

##this will return the unique lines from the first file.
comm -2 -3 <(sort FileOne.txt) <(sort FileTwo.txt) > myFile.txt

I run the script like this:

sh ./myfilename.sh

Please help me to solve it.


  • 3
    How do you run the script? I suspect you run it with sh and not bash.
    – terdon
    Jan 9 at 13:21
  • Yeah you should just run it with ./scriptname. Jan 9 at 13:22
  • running it like - sh myfilename.sh
    – Atul
    Jan 9 at 13:25
  • If you're new to bash scripting, I highly recommend this video series to get you started. Enjoy! Jan 9 at 16:11
  • Process substitution syntax i.e. <(...) works in bash but not in sh.
    – Raffa
    Jan 10 at 13:54

2 Answers 2


If needed, make the script executable first by running:

chmod +x myfilename.sh

Then, run the script like this:


Or run it explicitly with bash like this:

bash myfilename.sh

(These first two commands are essentially the same, since you have the bash shebang #!/bin/bash at the beginning of your script.)

DO NOT run like this:

sh myfilename.sh

Because then you are running the script with Dash (sh) and not with Bash (since your script has Bash-specific syntax).

  • +1 ... It might be worth noting that chmod +x is safer(ish) as it respects your environment's set umask(file mode creation mask) ... chmod a+x on the other hand should only be used if you mean it as it will set the executable bit for all(owner, group and others) regardless of the umask value.
    – Raffa
    Jan 10 at 13:33

The answer is similar to answer already posted, but giving an explanantion.

I thing you are running this script sh code.sh. This means you are using sh to run the script, but the first line (#!/bin/bash) implies it's been written for bash.

On some systems sh and bash are the same, but on others they are not; and, when invoked as sh, Bash turns off some non-POSIX features. So it's important to use the right shell and the right invocation.

Use bash code.sh or better still, make the script executable (chmod a+x code.sh) and then run it directly (./code.sh)

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