Question

This question is related to the thread here:

Today's date, minus X days in shell script

But because I’m now manipulating the variable, I started another thread.

As described above, I need to get today’s date minus 200 days, with the Year, Month, and Day in separate variables (in this question I’ll use 200, though in the other it’s 222). However, I need to represent January as 0, February as 1 (or 01), March as 2 (or 02), etc… I tried this:

MONTHS200=$(date -j -v-200d -v-1m +"%m")
if ${MONTHS200}=01; then 
${MONTH200}=0
else ${MONTHS200}=${MONTH200}
fi

But I get the error ./update_newdateformat.sh: line 20: 12=01: command not found ./update_newdateformat.sh: line 23: 12=: command not found The -v-1m works for all months except January, because it goes to 12, instead of 0

Answer 1

Here’s how to shift all the month number down by 1 n your script:

MONTHS200=$(date -j -v-320d +"%m")

# Remove leading zero if there is one, so it doesn't cause problems later
MONTHS200=${MONTHS200#0}

MONTHS200=$((MONTHS200-1))

Here is how to use if and = (assignment) syntax in shell:

if [[ "${MONTHS200}" == "01" ]]; then
    MONTHS200="0"
else
    MONTHS200=${AnotherVariable}
fi

Note that for numerical comparisons, you need to use:

• -eq instead of ==
• -ne instead of !=
• -lt instead of <
• -le instead of <=
• -gt instead of >
• -ge instead of >=

For example:

 if [[ "${MONTHS200}" -eq 1 ]]; then