bash-linux

Chaining Commands

| 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" |

---

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 |

---

| Task | Command |

|------|---------|

| List processes | ps aux |

| Find by name | ps aux \| grep node |

| Kill by PID | kill -9 |

| 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 |

---

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 |

---

| 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" |

---

| 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 |

---

```bash

#!/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 "$@"

```

---

Check if command exists

```bash

if command -v node &> /dev/null; then

echo "Node is installed"

fi

```

Default variable value

```bash

NAME=${1:-"default_value"}

```

Read file line by line

```bash

while IFS= read -r line; do

echo "$line"

done < file.txt

```

Loop over files

```bash

for file in *.js; do

echo "Processing $file"

done

```

---

| 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 |

---

Set options

```bash

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

```bash

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!