How do I remove leading zeroes from output of 'date' or avoid octal interpretation of such decimal numbers?

• In your case, you can simply disable zero padding by append - after % in the format string of date: %-H

  By default, date pads numeric fields with zeroes. The following optional flags may follow '%':

  • - (hyphen) do not pad the field
  • _ (underscore) pad with spaces
  • 0 (zero) pad with zeros
  • ^ use upper case if possible
  • # use opposite case if possible

  See date manual

• If you want to interpret number in different base, in bash

  • Constants with a leading 0 are interpreted as octal numbers.
  • A leading 0x or 0X denotes hexadecimal.
  • Otherwise, numbers take the form [base#]n, where base is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base

  So, to interpret a number as decimal, use 10#n form, eg. 10#09

  echo $((10#09*2))
  18
  

  See Arithmetic Evaluation section of bash manual.

Portably, you can easily remove a leading 0 from a variable. This leaves the variable unchanged if there is no leading 0.

eval $(date +"h=%H m=%M")
h=${h#0}
m=${m#0}
say "$h hours and $m minutes"

In bash, ksh or zsh, you can use ksh's additional glob patterns to remove any number of leading 0s. In bash, run shopt -s extglob first. In zsh, run setopt kshglob first.

eval $(date +"h=%H m=%M")
h=${h#+(0)}
m=${m#+(0)}
say "$h hours and $m minutes"

If you're trying to do comparisons in decimal with date values, I've found this method to be very effective:

let mymin=$(date '+1%M') ; let mymin=$mymin%100

That always yields a decimal value. So I can do this:

if [[ $mymin -le 1 ]]; then   # only 0 and 1 are true.

There's no problem with 08 or 09 this way. Using %10 instead of %100 gives you ten-minute ranges from 0 through 9. I also find the following gives decimal values, without leading zeros:

echo "$((10#$(date +%M)))"