When any person convicted of an offense is sentenced to imprisonment in the county jail, the court or magistrate shall order the defendant into the custody of the sheriff or other proper officer and shall issue to such officer a warrant of commitment. The officer shall deliver the convict, together with a copy of the warrant, to the jailer, in whose custody he or she shall remain in the jail of the proper county until the term of his or her confinement shall have expired or he or she shall have been pardoned or otherwise legally discharged.