Bash Is Not Zsh - Whitespace in variables

If you think bash and zsh are alike, ask someone who has had to spend hours trying to get a shell script to work after switching between shells.

One difference that many shell scripters encounter is the bash behavior of splitting a string with whitespaces when used with a for-in loop. The behavior makes it easy to quickly write scripts with minimal repetitions. For example:

ULIMIT_PARAMS="cpu as memlock fsize"
for p in $ULIMIT_PARAMS
do
  echo "*  soft  $p  unlimited" >> /etc/security/limits.conf
  echo "*  hard  $p  unlimited" >> /etc/security/limits.conf
done

Bash will separate the string at whitespaces, attempt to evaluate wildcards, and iterate through the elements: cpu, as, memlock, and fsize. The output will therefore be the addition of the following lines in /etc/security/limits.conf:

*  soft  cpu  unlimited
*  hard  cpu  unlimited
*  soft  as  unlimited
*  hard  as  unlimited
*  soft  memlock  unlimited
*  hard  memlock  unlimited
*  soft  fsize  unlimited
*  hard  fsize  unlimited

However, zsh would just see one long string “cpu as memlock fsize”, and this would be the output:

*  soft  cpu as memlock fsize  unlimited
*  hard  cpu as memlock fsize  unlimited

To get the above example to work with zsh, we can run the string through an echo command like this:

ULIMIT_PARAMS="cpu as memlock fsize"
for p in $(echo $ULIMIT_PARAMS)
do
  echo "*  soft  $p  unlimited" >> /etc/security/limits.conf
  echo "*  hard  $p  unlimited" >> /etc/security/limits.conf
done

With the added echo, the output will now be identical to what we see in bash.