for

Iterate using a list form.

for variable in list; do
    commands
done

Iterate using C style.

for (( init; condition; update )); do
    commands
done

Combined with brace expansion.

for variable in {1..10}; do
    commands
done

Combined with a file glob.

for file in *.txt; do
    commands
done

Iterates over a space-separated list in order.

sample_for_members.sh

#!/bin/bash
for member in "Yagami Iori" "Kusanagi Kyo" "Terry Bogard"; do
    echo "Member: $member"
done

The following example demonstrates this:

bash for_members.sh
Member: Yagami Iori
Member: Kusanagi Kyo
Member: Terry Bogard

You can also enter a for loop directly in the terminal. After pressing Enter following do, a > prompt appears — this means input is still expected. Enter done to execute.

for member in "Yagami Iori" "Kusanagi Kyo" "Terry Bogard"; do
    echo "Member: $member"
done
Member: Yagami Iori
Member: Kusanagi Kyo
Member: Terry Bogard

Use brace expansion {1..9} to specify a numeric range.

sample_multiply.sh

for i in {1..9}; do
    echo "3 × $i = $(( 3 * i ))"
done

The following example demonstrates this:

bash multiply.sh
3 × 1 = 3
3 × 2 = 6
3 × 3 = 9
...
3 × 9 = 27

Use a C-style counter loop to calculate the sum from 1 to 100.

sample_sum_100.sh

sum=0
for (( i=1; i<=100; i++ )); do
    (( sum += i ))
done
echo "Sum from 1 to 100: $sum"

Run the following command:

bash sum_100.sh
Sum from 1 to 100: 5050

Use a file glob (wildcard) to process files in the current directory.

sample_count_lines.sh

for f in *.php; do
    if [ -f "$f" ]; then
        echo "  $f ($(wc -l < "$f") lines)"
    fi
done

Run the following command:

bash count_lines.sh
  index.php (120 lines)
  ajax.php (85 lines)

Use continue to skip even numbers, and break to stop the loop when 7 is reached.

sample_skip_break.sh

for i in {1..10}; do
    if (( i % 2 == 0 )); then
        continue   # skip even numbers
    fi
    if (( i == 7 )); then
        break      # stop at 7
    fi
    echo "$i"
done

Run the following command:

bash skip_break.sh
1
3
5

Expand array elements with "${fighters[@]}" and iterate over them.

sample_fighters.sh

fighters=("Yagami Iori" "Kusanagi Kyo" "Terry Bogard" "Blue Mary")
for fighter in "${fighters[@]}"; do
    echo "Fighter: $fighter"
done

Run the following command:

bash fighters.sh
Fighter: Yagami Iori
Fighter: Kusanagi Kyo
Fighter: Terry Bogard
Fighter: Blue Mary

Common Mistake 1: for in $(ls) splits on spaces in filenames

for f in $(ls) uses command substitution, which is subject to word splitting. Filenames with spaces are broken into multiple items.

for f in $(ls *.txt); do echo "$f"; done
my
file.txt
（"my file.txt" was split）

Use a glob pattern directly to avoid word splitting.

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

Common Mistake 2: Not quoting array elements causes spaces to split them

Expanding ${array[@]} without quotes splits elements at every space character.

fighters=("Yagami Iori" "Terry Bogard")
for f in ${fighters[@]}; do echo "$f"; done
Yagami
Iori
Terry
Bogard

Always quote the expansion to preserve elements that contain spaces.

for f in "${fighters[@]}"; do echo "$f"; done
Yagami Iori
Terry Bogard

File globs ('*.php') can be used directly in a for loop, but using command substitution like 'for f in $(ls *.php)' can cause unexpected word splitting on filenames with spaces. Use globs directly for safety.

When processing a large number of files, piping find output to xargs is often more memory-efficient. For condition-based loops, use while / until.