Sorry, here is the same output with the formatting fixed:

Script:

timestamp="$(date  %s)"
#nonce=
key="dj0yJmk9bkZWbFVOeklYYjZHJmQ9WVdrOVRIaGtaRkpNTTJNbWNHbzlNVE0wTXpjMU9EVTJNZy0tJnM9Y29uc3VtZXJzZWNyZXQmeD1lNQ--"
method=PLAINTEXT
sig="f1fd94c079d55a6cda5f2ad18bc0ac4cdcd8f2b8"
callback=oob
wget -S -d https://api.login.yahoo.com/oauth/v2/get_request_token --post-data="oauth_version=1.0&oauth_nonce=8c76a87ffd3e4f48b53ed4b669b0b35f&oauth_timestamp=$timestamp&oauth_consumer_key=$key&oauth_signature_method=$method&oauth_signature=$sig&oauth_callback=$callback" -v

output:

Setting --post-data (postdata) to oauth_version=1.0&oauth_nonce=8c76a87ffd3e4f48b53ed4b669b0b35f&oauth_timestamp=1359222974&oauth_consumer_key=dj0yJmk9bkZWbFVOeklYYjZHJmQ9WVdrOVRIaGtaRkpNTTJNbWNHbzlNVE0wTXpjMU9EVTJNZy0tJnM9Y29uc3VtZXJzZWNyZXQmeD1lNQ--&oauth_signature_method=PLAINTEXT&oauth_signature=f1fd94c079d55a6cda5f2ad18bc0ac4cdcd8f2b8&oauth_callback=oob
Setting --verbose (verbose) to 1
DEBUG output created by Wget 1.13.4 on linux-gnu.

URI encoding = `UTF-8'
--2013-01-26 12:56:14--  https://api.login.yahoo.com/oauth/v2/get_request_token
Resolving api.login.yahoo.com (api.login.yahoo.com)... 68.142.197.104
Caching api.login.yahoo.com => 68.142.197.104
Connecting to api.login.yahoo.com (api.login.yahoo.com)|68.142.197.104|:443... connected.
Created socket 3.
Releasing 0x0000000000c44850 (new refcount 1).
Initiating SSL handshake.
Handshake successful; connected socket 3 to SSL handle 0x0000000000c44b70
certificate:
  subject: /C=US/ST=California/L=Santa Clara/O=Yahoo! Inc./OU=Yahoo/CN=*.login.yahoo.com
  issuer:  /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
X509 certificate successfully verified and matches host api.login.yahoo.com

---request begin---
POST /oauth/v2/get_request_token HTTP/1.1
User-Agent: Wget/1.13.4 (linux-gnu)
Accept: */*
Host: api.login.yahoo.com
Connection: Keep-Alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 326

---request end---
[POST data: oauth_version=1.0&oauth_nonce=8c76a87ffd3e4f48b53ed4b669b0b35f&oauth_timestamp=1359222974&oauth_consumer_key=dj0yJmk9bkZWbFVOeklYYjZHJmQ9WVdrOVRIaGtaRkpNTTJNbWNHbzlNVE0wTXpjMU9EVTJNZy0tJnM9Y29uc3VtZXJzZWNyZXQmeD1lNQ--&oauth_signature_method=PLAINTEXT&oauth_signature=f1fd94c079d55a6cda5f2ad18bc0ac4cdcd8f2b8&oauth_callback=oob]
HTTP request sent, awaiting response... 
---response begin---
HTTP/1.1 401 Forbidden
Date: Sat, 26 Jan 2013 17:56:14 GMT
P3P: policyref="http://info.yahoo.com/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA POL HEA PRE LOC GOV"
WWW-Authenticate: OAuth oauth_problem=signature_invalid
Connection: close
Transfer-Encoding: chunked
Content-Type: application/x-www-form-urlencoded
Cache-Control: private

---response end---

  HTTP/1.1 401 Forbidden
  Date: Sat, 26 Jan 2013 17:56:14 GMT
  P3P: policyref="http://info.yahoo.com/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA POL HEA PRE LOC GOV"
  WWW-Authenticate: OAuth oauth_problem=signature_invalid
  Connection: close
  Transfer-Encoding: chunked
  Content-Type: application/x-www-form-urlencoded
  Cache-Control: private
Registered socket 3 for persistent reuse.
Skipping 31 bytes of body: [oauth_problem=signature_invalid] done.
Authorization failed.

shell returned 6

Hey,

I'm not sure if you've solved this or not. I work with .NET but from what I can see your signature isn't constructed right. If you're using PLAINTEXT then all you need for your signature would be.. ...oauth_signature=f1fd94c079d55a6cda5f2ad18bc0ac4cdcd8f2b8&

Looks like you're just missing the ampersand character on the end of your oauth signature.