Compound 'if' statements with multiple expressions in Bash

I would like to recreate something like this

if ( arg1 || arg2 || arg 3) {}

And I did got so far, but I get the following error:

line 11: [.: command not found

if [ $char == $';' -o $char == $'\\' -o $char == $'\'' ]
then ...

I tried different ways, but none seemed to work. Some of the ones I tried.

For Bash, you can use the [[ ]] form rather than [ ], which allows && and || internally:

if [[ foo || bar || baz ]] ; then
  ...
fi

Otherwise, you can use the usual Boolean logic operators externally:

[ foo ] || [ bar ] || [ baz ]

...or use operators specific to the test command (though modern versions of the POSIX specification describe this XSI extension as deprecated -- see the APPLICATION USAGE section):

[ foo -o bar -o baz ]

...which is a differently written form of the following, which is similarly deprecated:

test foo -o bar -o baz

Bash's [[ ]] and (( )) are more powerful and flexible than [ ].

[[ ]] is for strings and (( )) is for integer logic and arithmetic
&& and || operators can be used inside [[ ]] and (( )), and () can be used for grouping
No need to quote variable expansions inside [[ ]] or (( )) - Bash doesn't do word splitting or globbing in these contexts
Inside (( )), there is no need for a $ behind variable names to expand them
[[ ]] and (( )) can span multiple lines, without the need for a line continuation with \

Using these, we can write clean, readable, and more reliable code.

Examples

Compound statements with integers

a=1 b=2 c=3
((a == 2 || (b == 2 && c == 3))) && echo yes                   # yields yes

Compound statements with strings

x=apple y=mango z=pear
[[ $x == orange || ($y == mango && $z == pear) ]] && echo yes  # yields yes

[ equivalents for the above statements, using {}

[ "$a" -eq 2 ] || { [ "$b" -eq 2 ] && [ "$c" -eq 3 ]; }
[ "$x" == orange ] || { [ $y == mango ] && [ "$z" == pear ]; }

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