cpufreq-info | grep -oe '[0-9].*GHz'

[0-9].*GHz

qDebug()<<infoStr.remove(QRegExp(".*frequency is ")).remove(QRegExp(" \\..*")).remove(QRegExp("\\.\\s+.*"));

QString str("cpufrequtils 008: cpufreq-info © Dominik Brodowski 2004-2009\nReport errors and bugs to cpufreq@vger.kernel.org, please.\nanalyzing CPU 0:\n driver: powernow-k8\n CPUs which run at the same hardware frequency: 0 1\n CPUs which need to have their frequency coordinated by software: 0 1\n maximum transition latency: 109 us.\n hardware limits: 800 MHz - 1.90 GHz\n available frequency steps: 1.90 GHz, 1.80 GHz, 1.60 GHz, 800 MHz\n available cpufreq governors: conservative, performance\n current policy: frequency should be within 800 MHz and 1.90 GHz.\n The governor performance may decide which speed to use\n within this range.\n current CPU frequency is 1.90 GHz.\nanalyzing CPU 1:\n driver: powernow-k8\n CPUs which run at the same hardware frequency: 0 1\n CPUs which need to have their frequency coordinated by software: 0 1\n maximum transition latency: 109 us.\n hardware limits: 800 MHz - 1.90 GHz\n available frequency steps: 1.90 GHz, 1.80 GHz, 1.60 GHz, 800 MHz\n available cpufreq governors: conservative, performance\n current policy: frequency should be within 800 MHz and 1.90 GHz.\n The governor performance may decide which speed to use\n within this range.\n current CPU frequency is 1.90 GHz.");

QRegExp rx("[current CPU frequency is ]\\d+\\.\\d+[ GHz]{1}");
rx.indexIn(str);
qDebug()<<rx.cap(0);