--trace and --trace-ascii

There are times when -v is not enough. In particular, when you want to store the complete stream including the actual transferred data.

For situations when curl does encrypted file transfers with protocols such as HTTPS, FTPS or SFTP, other network monitoring tools (like Wireshark or tcpdump) will not be able to do this job as easily for you.

For this, curl offers two other options that you use instead of -v.

--trace [filename] will save a full trace in the given file name. You can also use '-' (a single minus) instead of a file name to get it passed to stdout. You would use it like this:

$ curl --trace dump http://example.com

When completed, there's a 'dump' file that can turn out pretty sizable. In this case, the 15 first lines of the dump file looks like:

== Info: Rebuilt URL to: http://example.com/
== Info:   Trying 93.184.216.34...
== Info: Connected to example.com (93.184.216.34) port 80 (#0)
=> Send header, 75 bytes (0x4b)
0000: 47 45 54 20 2f 20 48 54 54 50 2f 31 2e 31 0d 0a GET / HTTP/1.1..
0010: 48 6f 73 74 3a 20 65 78 61 6d 70 6c 65 2e 63 6f Host: example.co
0020: 6d 0d 0a 55 73 65 72 2d 41 67 65 6e 74 3a 20 63 m..User-Agent: c
0030: 75 72 6c 2f 37 2e 34 35 2e 30 0d 0a 41 63 63 65 url/7.45.0..Acce
0040: 70 74 3a 20 2a 2f 2a 0d 0a 0d 0a                pt: */*....
<= Recv header, 17 bytes (0x11)
0000: 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b 0d HTTP/1.1 200 OK.
0010: 0a                                              .
<= Recv header, 22 bytes (0x16)
0000: 41 63 63 65 70 74 2d 52 61 6e 67 65 73 3a 20 62 Accept-Ranges: b
0010: 79 74 65 73 0d 0a                               ytes..

Every single sent and received byte get displayed individually in hexadecimal numbers.

If you think the hexadecimals are not helping, you can try --trace-ascii [filename] instead, also this accepting '-' for stdout and that makes the 15 first lines of tracing look like:

== Info: Rebuilt URL to: http://example.com/
== Info:   Trying 93.184.216.34...
== Info: Connected to example.com (93.184.216.34) port 80 (#0)
=> Send header, 75 bytes (0x4b)
0000: GET / HTTP/1.1
0010: Host: example.com
0023: User-Agent: curl/7.45.0
003c: Accept: */*
0049:
<= Recv header, 17 bytes (0x11)
0000: HTTP/1.1 200 OK
<= Recv header, 22 bytes (0x16)
0000: Accept-Ranges: bytes
<= Recv header, 31 bytes (0x1f)
0000: Cache-Control: max-age=604800

--trace-time

This options prefixes all verbose/trace outputs with a high resolution timer for when the line is printed. It works with the regular -v / --verbose option as well as with --trace and --trace-ascii.

An example could look like this:

$ curl -v --trace-time http://example.com
23:38:56.837164 * Rebuilt URL to: http://example.com/
23:38:56.841456 *   Trying 93.184.216.34...
23:38:56.935155 * Connected to example.com (93.184.216.34) port 80 (#0)
23:38:56.935296 > GET / HTTP/1.1
23:38:56.935296 > Host: example.com
23:38:56.935296 > User-Agent: curl/7.45.0
23:38:56.935296 > Accept: */*
23:38:56.935296 >
23:38:57.029570 < HTTP/1.1 200 OK
23:38:57.029699 < Accept-Ranges: bytes
23:38:57.029803 < Cache-Control: max-age=604800
23:38:57.029903 < Content-Type: text/html
---- snip ----

The lines are all the local time as hours:minutes:seconds and then number of microseconds in that second.

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