Test if a string has a period in it with bash

With any POSIX-like shell, assuming you want to run the command if $i does not contain a period as your example suggests, you'd write it:

case $i in
  (*.*) ;; # contains "."s, do nothing
  (*) drush "$i" command;;
esac

Note that with $(drush site-alias) being left unquoted, split+glob is performed on it. The splitting, which you want, being done on characters of $IFS (space, tab and newline by default (plus NUL in zsh), and the globbing, which you don't want would turn a /* word for instance into all the non-hidden files or directories in /.

On a GNU system, and with a shell with support for Ksh-style process substitution such as the GNU shell (bash), and assuming that command outputs one site-alias per line, you could do:

xargs -rd '\n' -a <(drush site-alias | grep -vF .) -I@ drush @ command

That has several advantages:

• no globbing
• properly splits on newline and newline only regardless of what $IFS happens to contain
• doesn't store the whole output in memory and starts to run drush commands as soon as drush site-alias starts to output something
• if any of the drush command fails, the failure will be reflected on xargs's exit status.

Note that the failure of drush site-alias if any is still ignored.

With zsh, you could do:

autoload zargs
site_aliases=( ${(f)"$(drush site-alias)"} ) || exit
zargs -I@ -- ${site_aliases:#*.*} -- drush @ command

Where:

• we also split on newline only by using the f parameter expansion flag (empty lines are discarded).
• we handle the failure of drush site-alias (here by exiting the script)
• ${site_aliases:#*.*} filters out (add a M parameter expansion flag to filter in instead) the elements that contain .
• like xargs, zargs returns a failure exit status if and of the commands fails.

You can do this with a pattern replace expansion:

for i in $(drush site-alias); do
  if [ -z "${i//[^.]/}" ]; then
     # no period
     drush "$i" command
  fi
done

Yes, I quoted "$i", which is probably something you should do when possible, it avoids surprises. Though in this case it won't matter.

Using the =~ bash operator.

for i in $(drush site-alias); do
  if ! [[ $i =~  \. ]]; then
     drush "$i" command
  fi
done

Just for the sake of another independent answer, I'm going to suggest using shell parameter expansions.

for i in $(drush site-alias)
do
    if [[ ${i%.*} == $i ]]
    then
        drush $i command
    fi
done

Strip out all the periods with sed. Then see if the original string equals the new string.

s="your test string here."

if [ "$(echo "$s" | sed 's/\.//g')" == "$s" ]; then 
   echo "No periods in $s" 
else echo "Periods in $s"; fi