Loops in Bash

Table of Contents

• for Loops
  • Create 200 files named file<number> skipping every even number 001-199
    • Using seq,
    • Using Brace Expansion (Parameter Expansion)
    • Using and C-style For-Loops
• while Loops
  • Loop with a Counter
  • Loop over lines from a file in bash
  • Loop over lines from a command
  • Forever (Infinite Loop)

for Loops

Create 200 files named file<number> skipping every even number 001-199

Using seq,

# Using `seq`
for i in $(seq 1 2 200); do  
    touch file${i}
done  

Using Brace Expansion (Parameter Expansion)

# Bash 4+ Exclusive: Brace expansion  
for i in {1..200..2}; do  
    touch file${i}
done  

Using and C-style For-Loops

# C-style loop  
for (( i=0; i<200; i+2 )); do  
    touch file${i}
done  

while Loops

Loop with a Counter

counter=0
while [[ $counter < 10 ]]; do
    printf "Counter: %d\n" "$counter"
    counter++
done

Loop over lines from a file in bash

while read -r line; do  
    echo "$line"  
done < file.txt  # Reading from `file.txt`

Loop over lines from a command (process substitution)

while read -r line; do  
    echo "$line"  
done < <(find . -maxdepth 1 -name '*.txt')  # All .txt files in current dir  

Forever (Infinite Loop)

while true; do  
    echo "This will run forever."  
done  

while :; do
    echo "This will also run forever."
done