Tips on Bash syntax

Recently I found in Bash some new syntax that was useful for me. I describe it here.

Make an array from a list returned by a command

If you capture the output of a command that usually prints a list on the standard output you don't get an array but a string with the list items delimited by a blank character. To transform this output into an array you have to surrond the "capturing" expression with another pair of brackets:

sites=($(find /srv -maxdepth 3 -type f -name "node_server.cfg"))

Array length

To get all the items in an array you can use the "@" or "*" character in place of the array index:

ports=${PORTLIST[@]}

Now, if you add a "#" character in front of the array name you get the array length:

portlistlen=${#PORTLIST[@]}

Another syntax for the "for" cycle

The "for" cycle accepts, besides the usual "for a in ..." syntax, another syntax more similar to that of the C language:

for (( i=0; i<$portlistlen; i++ ))
do
   ...
done