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I have to read an IP from def.cfg file that is set in a line named TERMINAL_IP (TERMINAL_IP = "192.168.0.140"), then do an append to the end of the def.cfg file with the last digit read that is not a 0 number, in this example have a 0 in the last digit so the value to show must be 4 and if the last number is .100 the value to show will be 1 but if the last number is .145 the value to show must be 5.

I'm using the following script to do that:

#!/bin/bash

CONFIG_FILE="def.cfg"

TERMINAL_IP=$(grep -oP '(?<=TERMINAL_IP = ).*' "$CONFIG_FILE")

if [[ -z "$TERMINAL_IP" ]]; then
  echo "TERMINAL_IP not found in the configuration file."
  exit 1
fi

LAST_DIGIT=$(echo "$TERMINAL_IP" | grep -oE '[0-9]+' | tail -n 1)

if [[ "$LAST_DIGIT" == "0" ]]; then
  # If the last digit is 0, take the second-to-last digit
  LAST_DIGIT=$(echo "$TERMINAL_IP" | grep -oE '[0-9]+' | tail -n 2 | head -n 1)
fi

echo "LSTD = \"${LAST_DIGIT}\"" >> "$CONFIG_FILE"

The problem is that instead append the number 4, it is appending the number 140, for some reason it does not isolate the number 4.

Any ideas to solve this?

I have to read an IP from def.cfg file that is set in a line named TERMINAL_IP (TERMINAL_IP = "192.168.0.140"), then do an append to the end of the def.cfg file with the last digit read that is not a 0 number, in this example have a 0 in the last digit so the value to show must be 4 and if the last number is .100 the value to show will be 1 but if the last number is .145 the value to show must be 5.

I'm using the following script to do that:

#!/bin/bash

CONFIG_FILE="def.cfg"

TERMINAL_IP=$(grep -oP '(?<=TERMINAL_IP = ).*' "$CONFIG_FILE")

if [[ -z "$TERMINAL_IP" ]]; then
  echo "TERMINAL_IP not found in the configuration file."
  exit 1
fi

LAST_DIGIT=$(echo "$TERMINAL_IP" | grep -oE '[0-9]+' | tail -n 1)

if [[ "$LAST_DIGIT" == "0" ]]; then
  # If the last digit is 0, take the second-to-last digit
  LAST_DIGIT=$(echo "$TERMINAL_IP" | grep -oE '[0-9]+' | tail -n 2 | head -n 1)
fi

echo "LSTD = \"${LAST_DIGIT}\"" >> "$CONFIG_FILE"

The problem is that instead append the number 4, it is appending the number 140, for some reason it does not isolate the number 4.

Any ideas to solve this?

• linux
• grep
• echo

Share Improve this question Follow edited yesterday Mario asked yesterday MarioMario 1355 bronze badges 5

• tail -n 1 outputs the last line, tail -c 1 would output the last character instead. – choroba Commented yesterday
• What's last and second last digit of 192.168.0.140? 140 and 0 or 0 and 4? – Cyrus Commented yesterday
• in .140, 4 is the last non 0 digit must to show. with tail -c 1 don't show nothing. – Mario Commented yesterday
• Remove + from your grep commands? – Cyrus Commented yesterday
• What should the output be if the value is 111.222.333.000? 3 or . or an error message or something else? – Ed Morton Commented 2 hours ago

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2 Answers 2

Sorted by: Reset to default 1

With GNU bash and its Parameter Expansion:

TERMINAL_IP="192.168.0.140"
TERMINAL_IP="${TERMINAL_IP/%0/}" # remove an existing trailing 0
echo "${TERMINAL_IP: -1:1}"      # extract last digit

Output:

4

Space before -1 is important.

If you're already using grep -P, you can use it to extract the last non-zero digit, too:

last_digit=$(grep -Po '(?<=TERMINAL_IP = ).*' "$CONFIG_FILE" \
             | grep -Po '[1-9](?=0*$)')

Note that $last_digit will be empty if the IP ends in .0.

Also note that I didn't use upper case letters for a non-environment variable.

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