bash script error let: -: syntax error: operand expected (error token is "-")

Question

Given the script below, can someone help me get past this error ? The script calculates days since the unix epoch and given the password expiration date, comes back telling me how many days till they are gonna get locked out. Its the let/math that is getting me. Ive tried quotes, different spacing around the minus operator all to no avail.

#!/usr/bin/bash
#
# Filename: pwx
# Description: Script to tell when A password for a user expires
# Usage: pwx username
#

function daysSince1970 {

    [[ -x /usr/bin/nawk ]] && AWK=/usr/bin/nawk || AWK=/usr/bin/awk
    date +"%j %Y" | $AWK  -v VERBOSE=$1 '
    {
            DAYOFYEAR=$1
            CURRENTYEAR=$2
            DAYS=-1 # Because it is not 1 day since 01/01/1970 until 02/01/1970.
            if (VERBOSE) { printf("%8s%8s%8s\n","Year","Days","Total") }
            for (YEAR=1970; YEAR < CURRENTYEAR; YEAR++) {
                    if (YEAR % 4 == 0) {
                            if (YEAR % 100 == 0) {
                                    if (YEAR % 1000 == 0) {
                                            YEARDAYS=366
                                    } else {
                                            YEARDAYS=365
                                    }
                            } else {
                                    YEARDAYS=366
                            }
                    } else {
                            YEARDAYS=365
                    }
                    DAYS+=YEARDAYS
                    if (VERBOSE) { printf("%8s%8d%8d\n",YEAR,YEARDAYS,DAYS) }
            }
            DAYS+=DAYOFYEAR
            if (VERBOSE) { printf("%8s%8d",YEAR,DAYOFYEAR) }
            printf("%8d\n",DAYS)
    }'
}

case $1 in

    "")
        echo -e "Usage: $0 username"
        ;;

    *)
        SEVENTY=$(daysSince1970)
        PWCD=$(grep $1 /etc/shadow| awk -F":" '{print $3}')
        PWED=$(grep $1 /etc/shadow| awk -F":" '{print $5}')

        let PWTIME=SEVENTY-PWCD

        if [[ $PWTIME -gt $PWED ]]
            then
            echo -e "Password expired"
        else
            let LEFT=PWED - $PWTIME  ####This is the line that is erroring out
            echo -e "$1 password good $LEFT to expire\n"
        fi
        ;;
esac

On which line is this error?

user1907906
– user1907906

2013-11-18 15:15:15 +00:00
Commented Nov 18, 2013 at 15:15 — user1907906
– user1907906, Commented Nov 18, 2013 at 15:15

Aaron Digulla · Accepted Answer · 2013-11-18 15:21:01Z

6

Remove the spaces. Instead of saying:

let LEFT=PWED - $PWTIME

say:

let LEFT=PWED-PWTIME

But this is brittle. Unless you know what you're doing, you should use bash's "Arithmetic Context":

((LEFT = PWED - $PWTIME))

edited Nov 18, 2013 at 15:21

Aaron Digulla

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answered Nov 18, 2013 at 15:15

devnull

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2 Comments

Aaron Digulla Over a year ago

or use ((LEFT = PWED - $PWTIME)) since it will handle spaces correctly.

devnull Over a year ago

@AaronDigulla Yes, arithmetic context is always better.

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