Bash check if file exists on startup

Question

I am trying to run a BASH script on a Debian machine. The script should run on every startup (so I put the .sh file in /etc/init.d) if the mac addr

Answer 1

Slightly modified version:

#!/bin/bash
macfile='/root/.mac.txt'
mac=$(/sbin/ifconfig | grep 'eth0' | tr -s ' ' | cut -d ' ' -f5)

# Shut down if file does not exist
if [ ! -f $macfile ]; then
    shutdown -h now
fi

# Verify MAC address against cached value
output=$(cat $macfile)
if [ "$mac" = "$output" ]; then
    echo "Server will start" 
else 
    shutdown -h now 
fi 

Explanation:

• Test for the existence of the file before you read from it
• The "[" and "]" characters must have a whitespace before and after them
• When running sub-commands, use the $( ... ) syntax instead of backticks