Echo is not printing the correct value for a variable

Question

I have a variable in my shell script which is not getting resolved properly at run time:

Input

#!/bin/sh
SERVER_ERL_ARGS="+K true +A30 +P 1048576 \
     -kernel inet_default_connect_options [{nodelay,true}]"
echo ${SERVER_ERL_ARGS}

Output:

+K true +A30 +P 1048576 -kernel inet_default_connect_options a

Any reason behind this kind of behavior and how can I correct it.

Answer 1

You have not quoted the variable expansion in your echo, and you have a file called a in the current directory.

The [{nodelay,true}] acts like a filename globbing pattern that will match any file whose name is any single character within the [...]. In your case it matches the name of the file called a in the current directory.

So, quote the variable, but it would be even better to use printf:

printf '%s\n' "$SERVER_ERL_ARGS"

Also note that ${variable} is exactly equivalent to $variable in all cases except when the expansion is part of a string where the immediately following character is valid in a variable name, like in "${variable}x".

See also:

• Security implications of forgetting to quote a variable in bash/POSIX shells

• Why is printf better than echo?