Question

I have written a small bash script called “isinFile.sh” for checking if the first term given to the script can be found in the file “file.txt”:

#!/bin/bash

FILE="file.txt"

if [ `grep -w "$1" $FILE` ]; then 
 echo "true"
else
 echo "false"
fi

However, running the script like

> ./isinFile.sh -x

breaks the script, since -x is interpreted by grep as an option.
So I improved my script

#!/bin/bash

FILE="file.txt"

if [ `grep -w -- "$1" $FILE` ]; then 
 echo "true"
else
 echo "false"
fi

using -- as an argument to grep. Now running

> ./isinFile.sh -x
false

works. But is using -- the correct and only way to prevent code/option injection in bash scripts? I have not seen it in the wild, only found it mentioned in ABASH: Finding Bugs in Bash Scripts.

Answer 1

grep -w -- ...

prevents that interpretation in what follows —

EDIT

(I did not read the last part sorry). Yes, it is the only way. The other way is to avoid it as first part of the search; e.g. ".{0}-x" works too but it is odd., so e.g.

grep -w ".{0}$1" ...

should work too.