How to protect yourself from shell injection?

Question

Command line

Hello!
The user enters some keyword, which is then substituted into grep
. What characters should be escaped so that nothing extra can be entered?

Answer 1

%  echo '$SHELL:' $SHELL; read i; echo '12\ndw\n3e\n/bin/zsh\n> '|grep "${i}"
$SHELL: /bin/zsh
> $SHELL
%
% echo '$SHELL:' $SHELL; read i; echo '12\ndw\n3e\n/bin/zsh\n> '|grep "${i}"
$SHELL: /bin/zsh
> $(cat /etc/passwd)
%

Symbols are not required. You need to escape the variable that is fed to grep :)