Script to read user input not running when run with sh interpreter

Question

This may be a duplicate of bash user input if, but the answers do not solved my problem, so I think there is something else.

I have the next script:

#!/bin/bash

echo "Do that? [Y,n]"
read input
if [[ $input == "Y" || $input == "y" ]]; then
        echo "do that"
else
        echo "don't do that"
fi

and when I do sh basic-if.sh

Also I have

#!/bin/bash

read -n1 -p "Do that? [y,n]" doit 
case $doit in  
  y|Y) echo yes ;; 
  n|N) echo no ;; 
  *) echo dont know ;; 
esac

and when I do sh basic-if2.sh

I think my bash has a problem because appereatly the other users didn't have these problems running those examples. Thanks

Inian · Accepted Answer · 2019-03-01 06:42:47Z

2

Running the script with sh scriptname overrides any default interpreter set inside your script. In your case the bourne shell (sh) runs the script instead of the bourne again shell (bash). The sh does not support [[ and the read command in its POSIX compliant form does not support -n flag.

In all likelihood, your sh in your system is not symlinked to bash and it is operating in itself as a POSIX compliant shell. Fix the problem by running

bash basic-if2.sh

or run it with a ./ before the script name there by making the system to look out for the interpreter in the first line of the file (#!/bin/bash). Instead of fixing the interpreter you could also do #!/usr/bin/env bash for the OS to look up where bash is installed and execute with that.

chmod a+x basic-if2.sh
./basic-if2.sh

You could additionally see if ls -lrth /bin/sh to see if its symlinked to dash which is a minimal POSIX compliant shell available on Debian systems.

edited Mar 1, 2019 at 6:42

answered Mar 1, 2019 at 6:25

Inian

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4 Comments

Nau Over a year ago

Oh, that fixed the problem, but now it created another, the change of color in the fonts \e[31m Example \e[0m are not recognized

Inian Over a year ago

@Delfin: I don't see them in your script above? How are you printing those colors?

Nau Over a year ago

I didn't place it for the minimum working example. But I am doing it this way: echo "\e[31m Example \e[0m"

Inian Over a year ago

@Delfin: It is because echo does not recognize ANSI color codes by default without doing echo -e. But the latter is not portable in POSIX systems. Recommend using printf '\e[31m Example \e[0m\n'

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