Bash Linux Patterns
Essential patterns for Bash on Linux/macOS.
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1. Operator Syntax
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"` |
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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 |
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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 |
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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 |
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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" |
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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 |
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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"
fiDefault variable value
NAME=${1:-"default_value"}Read file line by line
while IFS= read -r line; do
echo "$line"
done < file.txtLoop 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 |
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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 commandsTrap for cleanup
cleanup() {
echo "Cleaning up..."
rm -f /tmp/tempfile
}
trap cleanup EXIT---
Remember: Bash is text-based. Use
&&for success chains,set -efor safety, and quote your variables!
When to Use
This skill is applicable to execute the workflow or actions described in the overview.
Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.
