Foundations Updated 2026-09 View as Markdown

Loops

For each pass through the loop, arg takes on the value of each successive value in the list. Then the command(s) are executed.

bash for loop#

shell

# basic construct
for arg in [list]
do
 command(s)...
done

For each pass through the loop, arg takes on the value of each successive value in the list. Then the command(s) are executed.

shell

# loop on array member
NAMES=(Joe Jenny Sara Tony)
for N in ${NAMES[@]} ; do
  echo "My name is $N"
done

# loop on command output results
for f in $( ls prog.sh /etc/localtime ) ; do
  echo "File is: $f"
done

bash while loop#

shell

# basic construct
while [ condition ]
do
 command(s)...
done

The while construct tests for a condition, and if true, executes commands. It keeps looping as long as the condition is true.

shell

COUNT=4
while [ $COUNT -gt 0 ]; do
  echo "Value of count is: $COUNT"
  COUNT=$(($COUNT - 1))
done

bash until loop#

shell

# basic construct
until [ condition ]
do
 command(s)...
done

The until construct tests for a condition, and if false, executes commands. It keeps looping as long as the condition is false (opposite of while construct)

shell

COUNT=1
until [ $COUNT -gt 5 ]; do
  echo "Value of count is: $COUNT"
  COUNT=$(($COUNT + 1))
done

“break” and “continue” statements#

break and continue can be used to control the loop execution of for, while and until constructs. continue is used to skip the rest of a particular loop iteration, whereas break is used to skip the entire rest of loop. A few examples:

shell

# Prints out 0,1,2,3,4

COUNT=0
while [ $COUNT -ge 0 ]; do
  echo "Value of COUNT is: $COUNT"
  COUNT=$((COUNT+1))
  if [ $COUNT -ge 5 ] ; then
    break
  fi
done

# Prints out only odd numbers - 1,3,5,7,9
COUNT=0
while [ $COUNT -lt 10 ]; do
  COUNT=$((COUNT+1))
  # Check if COUNT is even
  if [ $(($COUNT % 2)) = 0 ] ; then
    continue
  fi
  echo $COUNT
done

Exercise

Try it

run this one locally

Expected output

Solution

#!/bin/bash
NUMBERS=(951 402 984 651 360 69 408 319 601 485 980 507 725 547 544 615 83 165 141 501 263 617 865 575 219 390 237 412 566 826 248 866 950 626 949 687 217 815 67 104 58 512 24 892 894 767 553 81 379 843 831 445 742 717 958 609 842 451 688 753 854 685 93 857 440 380 126 721 328 753 470 743 527)

# write your code here

for gg in ${NUMBERS[@]}; do

    if [ $gg == 237 ]; then
      break;
    elif [ $(($gg % 2)) == 0 ]; then
      echo $gg
    fi

done

Get the Bash agent pack

A battle-tested AGENTS.md, the review checklist, and the failure-mode cheat sheet for Bash. One email, then occasional updates when the tooling shifts. No course pitch.

Unsubscribe in one click. We never sell the list. Or just take the AGENTS.md now — no email needed.