mjhjmtu

I feel really stupid, but I am trying to learn how to use getopts so that I can have scripts with parsed input (although I think getopts could be better). I am trying to just write a simple script to return partition usage percentages. The problem is that one of my bash functions does not seem to like that I reference $1 as an variable within the function. The reason I reference $1 is because the get_percent function can be passed a mount point as an optional argument to display instead of all of the mount points.

The script

#!/usr/bin/bash

set -e
set -u
set -o pipefail

get_percent()
 if [ -n "$1" ] 
 then
 df -h $1 

usage()
 echo "script usage: $(basename $0) [-h] [-p] [-m mount_point]" >&2


# If the user doesn't supply any arguments, we run the script as normal
if [ $# -eq 0 ];
then
 get_percent
 exit 0
fi
# ...

The Output

$ bash thing.sh
thing.sh: line 8: $1: unbound variable

$ bash -x thing.sh
+ set -e
+ set -u
+ set -o pipefail
+ '[' 0 -eq 0 ']'
+ get_percent
thing.sh: line 8: $1: unbound variable

set -u will abort exactly as you describe if you reference a variable which has not been set. You are invoking your script with no arguments, so get_percent is being invoked with no arguments, causing $1 to be unset.

Either check for this before invoking your function, or use default expansions ($1-default will expand to default if not already set to something else).

This is the effect of set -u.

You could check $# inside the function and avoid referencing $1 if it is not set.

Since this is bash you can sidestep the check for $1 being set and just use "$@" (when double-quoted, this parameter disappears completely if it has no values, which avoids it being caught by set -u):

get_percent() awk 'NR>1 printf "%st%sn", $1, $5 '

I've also tweaked the rest of the line slightly so that you don't get spacetabspace between the two values you output but insead you get just a tab. If you really want the two invisible spaces then change the awk to use printf "%s t %sn", $1, $5.