What are the differences between -v, -i, -I, and -s parameters in cURL?

cURL provides multiple output control parameters for controlling the verbosity and format of requests. Understanding the differences between these parameters is important for debugging and daily use.

Parameter Comparison

Parameter	Full Name	Purpose	Output Content
-v	--verbose	Verbose mode	Complete request/response info
-i	--include	Include headers	Headers + Body
-I	--head	Headers only	Headers only (HEAD request)
-s	--silent	Silent mode	Body only (no progress)
-S	--show-error	Show errors	Use with -s

Detailed Explanation and Examples

1. -v (verbose) Verbose Mode

bash
# Show complete request and response process
curl -v https://api.example.com

# Output example:
# *   Trying 192.168.1.1:443...
# * Connected to api.example.com (192.168.1.1) port 443 (#0)
# > GET / HTTP/1.1
# > Host: api.example.com
# > User-Agent: curl/7.68.0
# > Accept: */*
# > 
# * Mark bundle as not supporting multiuse
# < HTTP/1.1 200 OK
# < Content-Type: application/json
# < Content-Length: 123
# < 
# {"status":"ok","data":[]}
# * Connection #0 to host api.example.com left intact

Output symbols:

• * - Connection and protocol info
• > - Sent request data
• < - Received response data
• { or } - SSL/TLS handshake info

2. -i (include) Include Headers

bash
# Show response headers and body
curl -i https://api.example.com

# Output example:
# HTTP/1.1 200 OK
# Content-Type: application/json
# Content-Length: 123
# Date: Mon, 01 Mar 2026 10:00:00 GMT
# 
# {"status":"ok","data":[]}

3. -I (head) Headers Only

bash
# Send HEAD request, get headers only
curl -I https://api.example.com

# Output example:
# HTTP/1.1 200 OK
# Content-Type: application/json
# Content-Length: 123
# Date: Mon, 01 Mar 2026 10:00:00 GMT
# Last-Modified: Sun, 28 Feb 2026 08:00:00 GMT
# ETag: "abc123"
# Cache-Control: max-age=3600

Note: -I automatically sends HEAD request, no body is retrieved.

4. -s (silent) Silent Mode

bash
# Silent mode, no progress info
curl -s https://api.example.com

# Only output body content
# {"status":"ok","data":[]}

# Combine with -S to show errors
curl -s -S https://api.example.com

# Combine with -o to output to file
curl -s https://api.example.com -o output.json

Combined Usage

bash
# Silent + show errors
curl -s -S https://api.example.com

# Verbose + output to file
curl -v https://api.example.com -o output.json 2>debug.log

# Include headers + silent
curl -i -s https://api.example.com

# Headers only + format
curl -I -s https://api.example.com | grep -i content-type

Practical Scenarios

Scenario 1: API Debugging

bash
# View complete request/response process
curl -v -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"test"}'

Scenario 2: Check Response Headers

bash
# Check cache headers
curl -I -s https://cdn.example.com/image.jpg | grep -i cache

# Check Content-Type
curl -I -s https://api.example.com/data | grep -i content-type

Scenario 3: Use in Scripts

bash
# Silent data retrieval and parsing
response=$(curl -s https://api.example.com/users)
echo "$response" | jq '.[] | .name'

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

Scenario 4: Debug SSL Issues

bash
# View SSL handshake process
curl -v https://api.example.com 2>&1 | grep -E "(SSL|TLS|certificate)"

# Save verbose log for analysis
curl -v https://api.example.com 2>ssl-debug.log

Other Related Parameters

bash
# --trace-ascii save detailed trace info
curl --trace-ascii debug.txt https://api.example.com

# --trace-time add timestamps
curl -v --trace-time https://api.example.com

# -w custom output format
curl -s -o /dev/null -w "Status: %{http_code}\nTime: %{time_total}s\n" https://api.example.com

# --progress-bar show progress bar
curl --progress-bar -O https://example.com/large-file.zip

Summary Recommendations

Scenario	Recommended Parameters
Daily debugging	-v
View response headers	-I or -i
Use in scripts	-s or -s -S
Performance testing	-s -o /dev/null -w ...
Download files	-s -O or --progress-bar

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