curl - Cliente HTTP e Transferência de Dados

Comandos abrangentes de curl para requisições HTTP, teste de API e transferência de dados em todas as plataformas.

Requisições HTTP Básicas

Requisições GET

Comando	Descrição
curl https://api.example.com	Solicitação GET básica
curl -v https://api.example.com	Saída detalhada com cabeçalhos
curl -i https://api.example.com	Incluir cabeçalhos de resposta
curl -I https://api.example.com	Solicitação HEAD apenas
curl -L https://example.com	Seguir redirecionamentos

Requisições POST

Comando	Descrição
curl -X POST https://api.example.com	Solicitação POST básica
curl -d "data" https://api.example.com	POST com dados
curl -d @file.json https://api.example.com	Dados POST de arquivo
curl -F "file=@upload.txt" https://api.example.com	Upload de arquivo

Outros Métodos HTTP

Comando	Descrição
curl -X PUT -d "data" https://api.example.com	Solicitação PUT
curl -X DELETE https://api.example.com/item/1	Solicitação DELETE
curl -X PATCH -d "data" https://api.example.com	Solicitação PATCH

Cabeçalhos e Autenticação

Cabeçalhos Personalizados

Comando	Descrição
curl -H "Content-Type: application/json" url	Definir tipo de conteúdo
curl -H "Authorization: Bearer token" url	Autenticação de token Bearer
curl -H "User-Agent: MyApp/1.0" url	User agent personalizado
curl -H "Accept: application/xml" url	Cabeçalho Accept

Métodos de Autenticação

Comando	Descrição
curl -u username:password url	Autenticação básica
curl -u username url	Solicitar senha
curl --oauth2-bearer token url	Token de portador OAuth2
curl --digest -u user:pass url	Autenticação Digest

Autenticação com Chave de API

# API key in header
curl -H "X-API-Key: your-api-key" https://api.example.com

# API key in query parameter
curl "https://api.example.com?api_key=your-api-key"

# Multiple headers
curl -H "Authorization: Bearer token" \
     -H "Content-Type: application/json" \
     https://api.example.com

Formatos de Dados

Dados JSON

# POST JSON data
curl -X POST \
     -H "Content-Type: application/json" \
     -d '\\\\{"name":"John","age":30\\\\}' \
     https://api.example.com/users

# JSON from file
curl -X POST \
     -H "Content-Type: application/json" \
     -d @data.json \
     https://api.example.com/users

Dados de Formulário

# URL-encoded form data
curl -d "name=John&age=30" https://api.example.com/users

# Multipart form data
curl -F "name=John" -F "age=30" https://api.example.com/users

# File upload with form data
curl -F "file=@document.pdf" \
     -F "description=Important document" \
     https://api.example.com/upload

Dados XML

# POST XML data
curl -X POST \
     -H "Content-Type: application/xml" \
     -d '<user><name>John</name><age>30</age></user>' \
     https://api.example.com/users

Operações de Arquivos

Baixar Arquivos

Comando	Descrição
curl -O https://example.com/file.zip	Baixar com nome original
curl -o myfile.zip https://example.com/file.zip	Baixar com nome personalizado
curl -C - -O https://example.com/file.zip	Retomar download interrompido
curl --limit-rate 100k -O url	Limitar velocidade de download

Enviar Arquivos

Comando	Descrição
curl -T file.txt ftp://server/path/	Carregar via FTP
curl -F "file=@upload.txt" url	Upload de arquivo HTTP
curl --upload-file file.txt url	Enviar upload de arquivo

Múltiplos Arquivos

# Download multiple files
curl -O https://example.com/file1.zip -O https://example.com/file2.zip

# Upload multiple files
curl -F "file1=@doc1.pdf" -F "file2=@doc2.pdf" https://api.example.com/upload

Opções Avançadas

Timeouts e Tentativas

Comando	Descrição
curl --connect-timeout 10 url	Tempo limite de conexão (segundos)
curl --max-time 30 url	Tempo total máximo
curl --retry 3 url	Tentar novamente em caso de falha
curl --retry-delay 5 url	Intervalo entre tentativas

Opções SSL/TLS

Comando	Descrição
curl -k url	Ignorar erros de certificado SSL
curl --cacert ca.pem url	Usar certificado de CA personalizado
curl --cert client.pem url	Usar certificado de cliente
curl --tlsv1.2 url	Forçar versão TLS

Proxy e Rede

Comando	Descrição
curl --proxy proxy.example.com:8080 url	Usar proxy HTTP
curl --socks5 proxy.example.com:1080 url	Use proxy SOCKS5
curl --interface eth0 url	Use interface de rede específica
curl --dns-servers 8.8.8.8 url	Usar servidores DNS personalizados

Saída e Formatação

Controle de Saída

Comando	Descrição
curl -s url	Modo silencioso (sem progresso)
curl -S url	Mostrar erros mesmo no modo silencioso
curl -o /dev/null url	Descartar saída
curl -w "%\\{http_code\\}" url	Mostrar apenas código de status HTTP

Informações de Resposta

# Get detailed timing information
curl -w "@curl-format.txt" https://example.com

# curl-format.txt content:
#     time_namelookup:  %\\\\{time_namelookup\\\\}\n
#        time_connect:  %\\\\{time_connect\\\\}\n
#     time_appconnect:  %\\\\{time_appconnect\\\\}\n
#    time_pretransfer:  %\\\\{time_pretransfer\\\\}\n
#       time_redirect:  %\\\\{time_redirect\\\\}\n
#  time_starttransfer:  %\\\\{time_starttransfer\\\\}\n
#                     ----------\n
#          time_total:  %\\\\{time_total\\\\}\n

Processamento de JSON

# Pretty print JSON with jq
curl -s https://api.example.com/users|jq '.'

# Extract specific fields
curl -s https://api.example.com/users|jq '.[]|.name'

# Filter results
curl -s https://api.example.com/users|jq '.[]|select(.age > 25)'

Teste e Depuração

Teste de API

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Test REST API endpoints

curl -X GET https://api.example.com/users curl -X POST -d ’\\{“name”:“John”\\}’ https://api.example.com/users curl -X PUT -d ’\\{“name”:“Jane”\\}’ https://api.example.com/users/1 curl -X DELETE https://api.example.com/users/1

Test with different content types

curl -H “Accept: application/json” https://api.example.com/users curl -H “Accept: application/xml” https://api.example.com/users

### Performance Testing
```bash
# Measure response time
curl -w "Total time: %\\\\{time_total\\\\}s\n" -o /dev/null -s https://example.com

# Test multiple requests
for i in \\\\{1..10\\\\}; do
  curl -w "%\\\\{time_total\\\\}\n" -o /dev/null -s https://example.com
done

Error Handling

# Check HTTP status codes
http_code=$(curl -s -o /dev/null -w "%\\\\{http_code\\\\}" https://example.com)
if [ $http_code -eq 200 ]; then
    echo "Success"
else
    echo "Error: HTTP $http_code"
fi

Configuration and Scripts

Configuration File

# ~/.curlrc configuration file
user-agent = "MyApp/1.0"
connect-timeout = 10
max-time = 30
show-error
silent

Bash Scripting

#!/bin/bash
# API testing script

BASE_URL="https://api.example.com"
API_KEY="your-api-key"

# Function to make authenticated requests
api_request() \\\\{
    local method=$1
    local endpoint=$2
    local data=$3

    curl -X "$method" \
         -H "Authorization: Bearer $API_KEY" \
         -H "Content-Type: application/json" \
         $\\\\{data:+-d "$data"\\\\} \
         "$BASE_URL$endpoint"
\\\\}

# Usage examples
api_request GET "/users"
api_request POST "/users" '\\\\{"name":"John","email":"john@example.com"\\\\}'

Security Best Practices

Secure Authentication

# Use environment variables for sensitive data
export API_TOKEN="your-secret-token"
curl -H "Authorization: Bearer $API_TOKEN" https://api.example.com

# Read credentials from file
curl -K credentials.txt https://api.example.com

# credentials.txt:
# header = "Authorization: Bearer your-token"

Certificate Verification

# Always verify SSL certificates in production
curl --cacert /path/to/ca-bundle.crt https://api.example.com

# For development only (not recommended for production)
curl -k https://self-signed.example.com

Common Use Cases

Web Scraping

# Download webpage
curl -L https://example.com > page.html

# Follow redirects and save cookies
curl -L -c cookies.txt -b cookies.txt https://example.com

# Set user agent to avoid blocking
curl -H "User-Agent: Mozilla/5.0 (compatible; bot)" https://example.com

API Integration

# GitHub API example
curl -H "Authorization: token your-github-token" \
     https://api.github.com/user/repos

# Weather API example
curl "https://api.openweathermap.org/data/2.5/weather?q=London&appid=your-api-key"

# Slack webhook example
curl -X POST \
     -H "Content-Type: application/json" \
     -d '\\\\{"text":"Hello from curl!"\\\\}' \
     https://hooks.slack.com/services/YOUR/SLACK/WEBHOOK

File Transfer

# Upload to cloud storage
curl -X PUT \
     -H "Authorization: Bearer token" \
     --upload-file document.pdf \
     https://api.storage.com/files/document.pdf

# Download with progress bar
curl --progress-bar -O https://example.com/largefile.zip

Troubleshooting

Common Issues

Problema	Solução
SSL certificate errors	Use -k for testing, fix certificates for production
Connection timeout	Increase --connect-timeout value
Slow downloads	Use --limit-rate to control bandwidth
Authentication failures	Verificar credenciais e método de autenticação

Debugging Commands

# Verbose output for debugging
curl -v https://example.com

# Trace all network activity
curl --trace trace.txt https://example.com

# Show only headers
curl -I https://example.com

# Test connectivity
curl -I --connect-timeout 5 https://example.com