How to write RegEx in Shell Script?

Question

How to write RegEx in Shell Script to fail the script with exit code 1 if any of the input parameters contain possible shell injection commands. One or two examples are sufficient. Plz help.

Here is the code snippet:

invalid_format="^.*[;&|].*$"

invalid_format2="rmdir"

if [ "$LOCAL_DIR" =~ "$invalid_format" -o "$LOCAL_DIR" =~ "$invalid_format2" ]; 
then

echo "Error! LOCAL_DIR cannot contain command chaining characters like ; && ||"

exit 1

fi

but, it fails with the error:

[: too many arguments

Answer 1

Use grep and pipe your string into grep , then check the return value.

#!/bin/bash
STRING_TO_CHECK="abc"
REGEX="b"

echo "$STRING_TO_CHECK" | grep -E "$REGEX"
if [ $? -eq 1 ]
then
  # regex not found
else
  # regex found
fi

Answer 2

Thanks Everyone.. here I got this get done.

invalid_format="(^.[;&|].$)|(\brmdir\b)|(\bls\b)|(rm\s-)|(\bping\b)"

if [[ $LOCAL_DIR =~ $invalid_format ]]; then

echo "Error! LOCAL_DIR cannot contain command chaining characters like ; && || or possible shell injection commands"

exit 1