What is the syntax for a bash for loop?

When working with scripting on a Linux system, one of the most useful tools is the bash for loop. The Bash for loop syntax has a few basic components that make it useful for performing complex tasks quickly and easily.

To begin, the for loop starts with the keyword "for" followed by a variable name that will represent each item in the sequence. For example, if you wanted to iterate over an array of numbers, you would use the variable "i" to represent each number. The next part of the syntax is the "in" keyword followed by the sequence that you want to iterate over. This could be words in an array or numbers in a range, but whatever it is, it must be enclosed in quotation marks.

The third part is where we define what we want to do with each element of our sequence. This can either be commands written directly into the code or passed as arguments using command substitution. Generally speaking if there are multiple commands better readability is achieved when they are separate lines enclosed within braces {} instead of just being written out within one line after done. For example, if we had an array called "numbers" and wanted to double each value we could use:

for i in {1..10}; do let "number[i]=$i*2"; done