Loops in Bash

Resources:

• https://www.cyberciti.biz/faq/bash-for-loop
• https://ryanstutorials.net/bash-scripting-tutorial/bash-loops.php

For Loops

Iterate a List of Words

Iterate through a series of space-delimited words.

words="abc def ghi"
for w in $words
do
  echo "$w"
done

# Output:
# abc
# def
# ghi

Iterate a Range of Integers

Iterate using range of numbers (inclusive on both sides).

for i in {1..3}
do
  echo "$i"
done

# Output:
# 1
# 2
# 3

The ranges can go in both directions

for i in {3..1}
do
  echo "$i"
done

# Output:
# 3
# 2
# 1

Increment can be specified too (as the 3rd value in {})

for i in {1..10..2}
do
  echo "$i"
done

# Output:
# 1
# 3
# 5
# 7
# 9

Three-expression Syntax

The typical for-loop syntax is possible as well.

for (( i=0; i<5; i++ ))
do
  echo "$i"
done

# Output:
# 1
# 2
# 3
# 4
# 5

Iterate Results of a Sub-command

# Let 'command' return values 'foo bar'

for result in $(command)
do
  echo "$result"
done

# Output
# foo
# bar