Ben Biddington

Whatever it is, it's not about "coding"

Posts Tagged ‘shell

Grepping lines with multiple matches

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I want to filter log files by matching lines that contains all of  set of matches (I don’t want to alternate them).

For example lines like:

RawURL /1.2/user/authorize?ip=

I want to match lines that contain the terms “RawURL” and “/1.2/user/authorize?” without resorting to piping multiple greps:

$ grep RawURL | grep /1.2/user/authorize? *.txt

This means I want a regexp like:


Translating to grep extended regex, this becomes:

$ grep -E RawURL.+/1.2/user/authorize *.txt

Note: There is no need to enforce non-greedy matching.

Regular expressions, character classes and special characters

The expression:


Is not equivalent to:


Because in the second one, the special character ‘.’ is no longer special. Character classes have all special characters turned off.

Written by benbiddington

23 October, 2009 at 13:37

Posted in development

Tagged with , , ,

Rake — shell task failure

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For my current project, we’re running cucumber as one of our tasks. Our report generation runs afterwards — which we need to happen regardless of cucumber’s exit code (cucumber exits with code 1 when any tests fail).

Handling shell task failure

We noticed that if cucumber fails, rake exits immediately — without running our subsequent report tasks.

We’re running cucumber with rake’s ruby function — which runs the ruby interpreter in its own process by invoking a shell command.

Pseudo-stacktrace (irrelevant source lines omitted):

Shell::CommandProcessor.system(command, *opts)
Rake::Win32.rake_system(*cmd)*args, &block)
FileUtils.ruby(*args, &block)

The key to this is the behaviour of rake’s Examining the source shows:

If it is not supplied a block, and the shell command fails, and rake exits with error status.

Aside: For some reason, Kernel.system echoes errors.


This task will cause rake to exit immediately with status 1:

task 'this-one-fails' do

while the following task does not cause rake to terminate  normally, any subsequent task will still run:

path = File.expand_path(File.dirname(__FILE__) + ‘/output/cucumber-manual.txt’)
cuke_path = ‘C:/ruby/lib/ruby/gems/1.8/gems/cucumber-0.3.3/bin/cucumber’
ruby(“#{cuke_path} -h > ‘#{path}'”) do |success, exit_code|
puts “Exited with code: #{exit_code}” if !success
task 'this-one-succeeds' do
    ruby("xxx") do |success, exit_code|
        puts "Exited with code: #{exit_code.exitstatus}" unless success

Getting the last exit status

The $? variable contains the status of the last child process to terminate. This may be useful if steps subsequent to the failed one require this information.

Written by benbiddington

16 May, 2009 at 16:45