Bash Command Chaining Mastery: The Ultimate Cheat Sheet

chaining.md

🔗 Bash Command Chaining Mastery: The Ultimate Cheat Sheet

🔗 Basic Command Chaining

Operator	Description	Example
;	📊 Run commands sequentially	echo "Hello"; echo "World"
&&	✅ Run next command only if previous succeeds	mkdir dir && cd dir
||	❌ Run next command only if previous fails	ping -c1 google.com || echo "Offline"
|	🚿 Pipe output of one command to another	ls -l | grep ".txt"

🔀 Command Grouping

Syntax	Description	Example
( ... )	🐣 Run commands in a subshell	(cd /tmp && ls) | grep log
{ ...; }	📦 Run commands in current shell	{ echo "Start"; ls; echo "End"; }

🔄 Loop Constructs

Syntax	Description	Example
for	🔁 Iterate over a list	for i in {1..5}; do echo $i; done
while	🔄 Run while condition is true	while true; do date; sleep 1; done
until	🔄 Run until condition is true	until ping -c1 google.com; do sleep 5; done

🔀 Conditional Execution

Syntax	Description	Example
if...then...fi	🔍 Conditional execution	if [ -f file.txt ]; then echo "Exists"; fi
case...esac	🔢 Multi-way decision	case $var in 1) echo "One";; 2) echo "Two";; esac

🔣 Input/Output Redirection

Operator	Description	Example
>	📤 Redirect stdout to file (overwrite)	echo "Hello" > file.txt
>>	📥 Redirect stdout to file (append)	echo "World" >> file.txt
<	📥 Redirect file to stdin	sort < unsorted.txt
2>	🚨 Redirect stderr to file	gcc program.c 2> errors.log
&>	📊 Redirect both stdout and stderr	command &> output.log

🔗 Advanced Chaining Techniques

Technique	Description	Example
xargs	🔨 Build command lines from standard input	find . -name "*.txt" | xargs grep "pattern"
tee	🔱 Send output to both file and stdout	echo "log" | tee -a logfile.txt
command substitution	🔄 Use output of a command as argument	echo "Today is $(date +%A)"
process substitution	🔄 Use output of command as file	diff <(sort file1) <(sort file2)

🎛️ Job Control

Command	Description	Example
&	🏃‍♂️ Run command in background	long_running_command &
jobs	📋 List background jobs	jobs
fg	▶️ Bring job to foreground	fg %1
bg	🏃‍♂️ Resume job in background	bg %2
wait	⏳ Wait for background jobs to finish	wait %1

🏆 Pro Tips

1. 📚 Use set -e at the start of your script to exit on any command failure
2. 🔍 Use set -x for debugging to print each command before execution
3. 🔢 Use $? to check the exit status of the last command
4. 🔀 Combine && and \|\| for if-else like behavior: command && success_command \|\| failure_command
5. 🔁 Use while read to process file contents line by line
6. 📥 Use <<EOF for here-documents to pass multi-line input to a command
7. 🔒 Use set -o noclobber to prevent accidental file overwrites with >
8. 🔣 Remember that 2>&1 redirects stderr to stdout
9. 🔨 Use trap to set up commands that run on script exit or on signals
10. 📊 Use time command to measure execution time of commands or scripts

📜 Example: Combining Multiple Techniques

#!/bin/bash
set -e

# Function to process files
process_file() {
    echo "Processing $1"
    # Simulating processing with sleep
    sleep 1
}

# Find all .txt files and process them in parallel
find . -name "*.txt" | xargs -I {} -P 4 bash -c 'process_file "$@"' _ {}

# Wait for all background jobs to finish
wait

# Check if any errors occurred
if [ $? -eq 0 ]; then
    echo "All files processed successfully" | tee success.log
else
    echo "Some errors occurred during processing" | tee error.log >&2
fi

# Cleanup temporary files
rm -f *.tmp && echo "Cleanup completed" || echo "Cleanup failed"

Remember, with great power comes great responsibility. Use these techniques wisely to create efficient and readable Bash scripts! 🚀💻