Explaining “08: value too great for base (error token is “08”)” in Bash

The aim of this page📝 is to explain the issue of octal interpretation in bash scripts when dealing with numbers containing leading zeros, using a specific example of calculating week numbers.

• By default, bash interprets numbers with leading zeros as octal numbers.
• Octal numbers only use digits from 0 to 7, causing issues with numbers like 08 or 09.
• Using 10# before a variable explicitly specifies decimal interpretation, avoiding octal errors.

History:

• The octal interpretation behavior in bash is inherited from the C programming language.
• Octal numbers were commonly used in early computing due to their compact representation.

Risks:

• Incorrectly interpreting numbers as octal can lead to unexpected results in calculations.
• It can be a common source of errors when handling numerical data in bash scripts.

Example code snippets:

# Original command causing error
next_CW=$((CW + 1))
# Corrected command using 10# to specify decimal interpretation
next_CW=$((10#$CW + 1))

`week`

• I have this short week function that gives me this/next week snippet I put in tickets sometimes
• It broke on week 8 with

bash: 08: value too great for base (error token is "08")

function week() {
    CW=$(date +%V)
    year=$(date +%Y)
    next_CW=$((10#$CW + 1)) #BEFORE: this was next_CW=$(($CW + 1))

if [ "$1" == "." ]; then
        echo "---CURRENT WEEK---"
        start_date=$(date -j -f "%Y %V" "$year $CW" "+%Y-%m-%d")
        echo "(CW $CW commencing $start_date)"
        this_week_eta="The work is scheduled for this week (CW $CW commencing $start_date)"
        echo "$this_week_eta"
        echo "$this_week_eta" | pbcopy
        echo "~~~> MrD: clipping OK!"
    elif [ "$1" == "+" ]; then
        start_date=$(date -j -f "%Y %V" "$year $next_CW" "+%Y-%m-%d")
        echo "---NEXT WEEK---"
        echo "(CW $next_CW commencing $start_date)"
        next_week_eta="The work is scheduled for the next week (CW $next_CW commencing $start_date)"
        echo "$next_week_eta"
        echo "$next_week_eta" | pbcopy
        echo "~~~> MrD: clipping OK!"
    fi
}

ANKI

Question:
What is the default behavior of bash when dealing with numbers containing leading zeros?
Answer:
Bash interprets numbers with leading zeros as octal by default.

Question:
How can you avoid octal interpretation issues in bash?
Answer:
You can use the syntax `10#` before a variable to explicitly specify decimal interpretation.