Apple includes a handy commmand-line tool called agvtool for updating Xcode project version numbers via Terminal. Run the tool with a build version or marketing version, and it modifies a couple fields:
$ agvtool new-version -all "1.2.3.4"
Setting version of project sample to:
1.2.3.4.
Also setting CFBundleVersion key (assuming it exists)
Updating CFBundleVersion in Info.plist(s)...
Updated CFBundleVersion in "sample.xcodeproj/../sample-Info.plist" to 1.2.3.4
$ agvtool new-marketing-version "1.2.3 (4)"
Setting CFBundleShortVersionString of project sample to:
1.2.3 (4).
Updating CFBundleShortVersionString in Info.plist(s)...
Updated CFBundleShortVersionString in "sample.xcodeproj/../sample-Info.plist" to 1.2.3 (4)
Google "agvtool" and you'll inevitably come across two great posts: Apple's Chris Hanson covering the tool's goal and Red Sweater's Daniel Jalkut discussing its automation. They go into much greater detail.
Keep two caveats in mind when using agvtool:
Key Existence: agvtool only modifies project.pbxproj and Info.plist where it sees specific keys. It doesn't add an entry, and CURRENT_PROJECT_VERSION only appears in the project file after you change the value in Versioning->Current Project Version.
Key Replacement: agvtool modifies the values for specific keys in these two files. It doesn't search through the files and replace the keys with the values. So, "${CURRENT_PROJECT_VERSION} Copyright 2010" doesn't become "1.2.3.4 Copyright 2010".
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