Control flow in Bash

Last reviewed May 28, 2026 Content v20260528

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none

Means

Read / quiz

Reading

~1 min

Level

beginner

This lesson

This lesson teaches Control flow in Bash: the syntax, patterns, and safety habits you need before advancing in Bash.

Coroutines replace callback hell on Android and in Ktor—structured concurrency is interview-critical.

You will apply Control flow in Bash in contexts like: CI jobs, server maintenance, local dev automation, and Git hooks.

Read each lesson, copy bash examples into your own terminal, and complete the lesson MCQs—there is no in-browser runner for security reasons.

When you can explain the previous lesson's ideas without copying starter code.

Bash supports if, case, and loops (for, while). Tests use [[ ]] (Bash) or [ ] (POSIX test)—prefer [[ ]] in Bash scripts.

if and [[ ]]

score=85
if [[ $score -ge 90 ]]; then
  echo "A"
elif [[ $score -ge 80 ]]; then
  echo "B"
else
  echo "C or below"
fi

-ge means greater than or equal (numeric test inside [[ ]]).

for f in *.txt; do
  echo "file: $f"
done

for n in 1 2 3; do
  echo "n=$n"
done

for f in *.txt loops over matching files—glob order matters for reproducibility.

count=0
while [[ $count -lt 3 ]]; do
  echo "count=$count"
  count=$((count + 1))
done

Q: if vs [[ ]]?
A: [[ is a Bash keyword with safer parsing than the external [ command.
Q: for file in *.log purpose?
A: Runs the loop body once per matching filename.

Tip: Prefer [[ ]] in Bash scripts; use [ ] when you must stay POSIX-sh compatible.

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