List l = new ArrayList{a@yahoo.com, b@gmail.com}
def gmail = ['sh','-c','grep "clientLogin="$l.get(0) file.txt' | grep gmail | wc -l ]
def yahoo = ['sh','-c','grep "clientLogin="$l.get(1) file.txt' | grep yahoo| wc -l ]

def gmail = ['sh','-c','grep "clientLogin=${l.get(0)}" file.txt' | grep gmail | wc -l ]

def gmail = ['sh','-c','grep "clientLogin=a@yahoo.com" file.txt' | grep gmail | wc -l ]

Into the domain clientLogin=a@yahoo.com exit on 12/01/2008 etc..

def ex = ['sh','-c','grep "domain clientLogin=$client" file.txt'| grep "something more" | wc -l]

def ex = ['grep', "$client", 'file.txt']

def file = new File("file.txt")
file.delete() // clear out old version for multiple runs
file <<  """
foobar clientLogin=a@yahoo.com baz quux   # should match a@yahoo.com
foobar email=a@yahoo.com baz quux
foobar email=b@gmail.com bal zoom
foobar clientLogin=a@yahoo.com baz quux   # should match a@yahoo.com
foobar clientLogin=b@gmail.com bal zoom   # should match b@gmail.com
foobar email=b@gmail.com bal zoom
"""

def emailList = ["a@yahoo.com", "b@gmail.com"]
def emailListGroup = emailList.join('|')
def pattern = /(?m)^.*clientLogin=($emailListGroup).*$/

def resultMap = [:]

(file.text =~ pattern).each { fullLine, email ->
    resultMap[email] = resultMap[email] ? resultMap[email] + 1 : 1
}

assert resultMap["a@yahoo.com"] == 2
assert resultMap["b@gmail.com"] == 1

def client = 'foo@bar.com'
def ex = ['grep', "$client", 'file.txt']

def proc = ex.execute()
proc.waitFor()

println "return: ${proc.exitValue()}"
println "stderr: ${proc.err.text}"
println "stdout: ${proc.in.text}"

"${l.get(0)}"

List l = new ArrayList{a@yahoo.com, b@gmail.com}
def gmail = ['sh','-c','grep "clientLogin="${l.get(0)} file.txt' | grep gmail | wc -l ]
def yahoo = ['sh','-c','grep "clientLogin="${l.get(1)} file.txt' | grep yahoo| wc -l ]