Loops

Iterate with for, while, and until, and read files safely.

for loops (words)

for x in a b c; do
  echo "$x"
done

for f in src/*.js; do
  [[ -e $f ]] || continue  # handle no-match when nullglob is off
  echo "$f"
done

C-style loop

for (( i = 0; i < 3; i++ )); do
  echo "$i"
done

while / until

count=0
while (( count < 3 )); do
  echo "$count"; ((count++))
done

until ping -c1 example.com &>/dev/null; do
  sleep 1
done

Reading files safely

# Avoid: while read line; do ...; done < file   # breaks on spaces/backslashes
# Prefer:
while IFS= read -r line; do
  printf '%s\n' "$line"
done < input.txt

IFS= prevents trimming; -r disables backslash escapes.

Loop control

• break to exit the loop
• continue to skip to next iteration

Summary

• Use for for words/globs, C-style for counters, while/until for conditions
• Read files with IFS= read -r to preserve contents