The following AppleScript will take the contents of the clipboard and replace it with the URL prepended:
set the clipboard to "http://bugzilla_server/bugzilla/show_bug.cgi?id=" & (the clipboard)
You can compile that to an AppleScript scpt and make it available in a Scripts folder or compile it to a launchable app:
osacompile -e 'set the clipboard to "http://bugzilla_server/bugzilla/show_bug.cgi?id=" & (the clipboard)' -o replacebug.scpt # or -o replacebug.app
If your primary use case for this is in composing mail in Mail.app, this may not be the most user-friendly approach, though. If you are using Snow Leopard (10.6), a simpler solution is to take advantage of the new Text Substitution feature. Open the System Preferences -> Language & Text preference panel, select the Text tab, and click + to add a new substitution, perhaps:
Replace With
(b) http://bugzilla_server/bugzilla/show_bug.cgi?id=
Then, in Mail.app, start a New Message and, with the cursor clicked within the text body, do a Control click of the mouse to bring up the contextual menu. From it, select Substitutions -> Text Replacement. From now on, as you are typing in the text body of the email when you type:
(b)777
the (b) will automatically change to the URL text you saved:
http://bugzilla_server/bugzilla/show_bug.cgi?id=777
This will also work in other Cocoa text-enabled applications like Safari.
EDIT:
When talking about composing URL links in email, there are at least three different formats of email, each with a different solution. Since you don't say which kind you are using, I'll cover all three:
Plain text format - There's no way to "hide" the URL in the composed email although some email readers might present a clickable link for a plain-text URL.
HTML-formatted email - Apple's Mail.app does not support composing email in this format although it will display it. Using some other mail writer client or your own program, it's easy enough to compose a link using a standard HTML anchor <a href=...> tag.
Rich Text Format email - AFAIK, this is the only way to compose a URL link with Mail.app. Unfortunately, there does not appear to be an easy way to directly create an RTF hyperlink using AppleScript commands. Based on a suggestion here, this is a way to do it by creating a modifiable RTF template via the clipboard.
- In
TextEdit.app, create a new Document window.
- Insert the text you want to appear in the email, i.e.
777.
- Select the text (⌘A) then add a link (⌘K). Enter the full URL also with
777 into the "Link destination" field; click OK.
- Modify the text format as desired with Format menu commands.
- Save the file (⇧⌘S) as
temp.rtf with File Format -> Rich Text Format.
- Close the document window.
- Open a document window (⌘O) selecting file
temp.rtf and selecting Ignore rich text commands.
Insert the following before the first line in the file:
#!/bin/sh
sed -e "s/777/$(pbpaste -Prefer txt)/g" <<EOF | pbcopy -Prefer rtf
Append EOF as a separate line at the end of the file.
It should now look something like this:
#!/bin/sh
sed -e "s/777/$(pbpaste -Prefer txt)/g" <<EOF | pbcopy -Prefer rtf
{\rtf1\ansi\ansicpg1252\cocoartf1038\cocoasubrtf250
{\fonttbl\f0\fswiss\fcharset0 Helvetica;}
{\colortbl;\red255\green255\blue255;}
\margl1440\margr1440\vieww9000\viewh8400\viewkind0
\pard\tx720\tx1440\tx2160\tx2880\tx3600\tx4320\tx5040\tx5760\tx6480\tx7200\tx7920\tx8640\ql\qnatural\pardirnatural
{\field{\*\fldinst{HYPERLINK "http://bugzilla_server/bugzilla/show_bug.cgi?id=777"}}{\fldrslt
\f0\fs24 \cf0 777}}}
EOF
Save this as a Plain Text file and execute directly as a shell script or call it via the AppleScript do shell script command.
This kind of solution will work with most other applications that support Rich Text format.