result would be

exa = exp( cos(arg) , sin(arg) ) * fabs(arg2)+ sqrt(carg(arg3)) + sqrt(carg(arg4)*carg(arg5)+carg(arg5)*carg(arg5));

Really? Why do you go from cabsl to fabs instead of replacing it with abs? Also, your bracket counts seem to differ between the before and after examples.

Assuming that you didn't mean that and really wanted abs and the same number of brackets and correcting the arbitrary whitespace:

#!/usr/bin/env perl 
use strict;
use warnings;
use Test::More tests => 1;

my $have = 'exa=cexpl ( ccosl (arg), csinl ( arg) ) * cabsl (arg2) + c
+sqrtl ( cargl(arg3)) + csqrtl(cargl(arg4) * cargl(arg5) + cargl (arg5
+) * cargl(arg5));';
my $want = 'exa = exp( cos(arg) , sin(arg) ) * abs(arg2)+ sqrt(carg(ar
+g3)) + sqrt(carg(arg4)*carg(arg5)+carg(arg5)*carg(arg5));';

# Remove apparently arbitrary spaces for the purposes of validation
$have =~ s/ +//g;
$want =~ s/ +//g;

for my $term (qw/exp cos sin abs sqrt carg/) {
    $have =~ s/\b[cf]? ${term} [fl]?/$term/xg;
}
is ($have, $want, 'Match');
[download]