2. File Operations

Essential Commands

Task	Command
List all	`ls -la`
Find files	`find . -name "*.js" -type f`
File content	`cat file.txt`
First N lines	`head -n 20 file.txt`
Last N lines	`tail -n 20 file.txt`
Follow log	`tail -f log.txt`
Search in files	`grep -r "pattern" --include="*.js"`
File size	`du -sh *`
Disk usage	`df -h`

3. Process Management

Task	Command
List processes	`ps aux`
Find by name	`ps aux \| grep node`
Kill by PID	`kill -9 <PID>`
Find port user	`lsof -i :3000`
Kill port	`kill -9 $(lsof -t -i :3000)`
Background	`npm run dev &`
Jobs	`jobs -l`
Bring to front	`fg %1`

4. Text Processing

Core Tools

Tool	Purpose	Example
`grep`	Search	`grep -rn "TODO" src/`
`sed`	Replace	`sed -i 's/old/new/g' file.txt`
`awk`	Extract columns	`awk '{print $1}' file.txt`
`cut`	Cut fields	`cut -d',' -f1 data.csv`
`sort`	Sort lines	`sort -u file.txt`
`uniq`	Unique lines	`sort file.txt \| uniq -c`
`wc`	Count	`wc -l file.txt`

5. Environment Variables

Task	Command
View all	`env` or `printenv`
View one	`echo $PATH`
Set temporary	`export VAR="value"`
Set in script	`VAR="value" command`
Add to PATH	`export PATH="$PATH:/new/path"`

6. Network

Task	Command
Download	`curl -O https://example.com/file`
API request	`curl -X GET https://api.example.com`
POST JSON	`curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' URL`
Check port	`nc -zv localhost 3000`
Network info	`ifconfig` or `ip addr`

7. Script Template

#!/bin/bash
set -euo pipefail  # Exit on error, undefined var, pipe fail

# Colors (optional)
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m'

# Script directory
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# Functions
log_info() { echo -e "${GREEN}[INFO]${NC} $1"; }
log_error() { echo -e "${RED}[ERROR]${NC} $1" >&2; }

# Main
main() {
    log_info "Starting..."
    # Your logic here
    log_info "Done!"
}

main "$@"

8. Common Patterns

Check if command exists

if command -v node &> /dev/null; then
    echo "Node is installed"
fi

Default variable value

NAME=${1:-"default_value"}

Read file line by line

while IFS= read -r line; do
    echo "$line"
done < file.txt

Loop over files

for file in *.js; do
    echo "Processing $file"
done

9. Differences from PowerShell

Task	PowerShell	Bash
List files	`Get-ChildItem`	`ls -la`
Find files	`Get-ChildItem -Recurse`	`find . -type f`
Environment	`$env:VAR`	`$VAR`
String concat	`"$a$b"`	`"$a$b"` (same)
Null check	`if ($x)`	`if [ -n "$x" ]`
Pipeline	Object-based	Text-based

10. Error Handling

Set options

set -e          # Exit on error
set -u          # Exit on undefined variable
set -o pipefail # Exit on pipe failure
set -x          # Debug: print commands

Trap for cleanup

cleanup() {
    echo "Cleaning up..."
    rm -f /tmp/tempfile
}
trap cleanup EXIT

Remember: Bash is text-based. Use && for success chains, set -e for safety, and quote your variables!

Operator	Meaning	Example
`;`	Run sequentially	`cmd1; cmd2`
`&&`	Run if previous succeeded	`npm install && npm run dev`
`\|\|`	Run if previous failed	`npm test \|\| echo "Tests failed"`
`\|`	Pipe output	`ls \| grep ".js"`

bash-linux

Bash Linux Patterns

1. Operator Syntax

Chaining Commands