043 while loops kho tài liệu training

While Loops LinuxTrainingAcademy.com What You Will Learn ● ● ● While loops Infinite loops Loop control ○ ○ ○ ● ● Explicit number of times User input Command exit status Reading files, line-by-line break and continue LinuxTrainingAcademy.com While Loop Format while [ CONDITION_IS_TRUE ] command command command N done LinuxTrainingAcademy.com While Loop Format while [ CONDITION_IS_TRUE ] # Commands change the condition command command command N done LinuxTrainingAcademy.com Infinite Loops while [ CONDITION_IS_TRUE ] # Commands NOT change # the condition command N done LinuxTrainingAcademy.com Infinite Loops while [ true ] command N sleep done LinuxTrainingAcademy.com Example - Loop Times INDEX=1 while [ $INDEX -lt ] echo "Creating project-${INDEX}" mkdir /usr/local/project-${INDEX} ((INDEX++)) done LinuxTrainingAcademy.com Output - Loop Times Creating Creating Creating Creating Creating project-1 project-2 project-3 project-4 project-5 LinuxTrainingAcademy.com Example - Checking User Input while [ "$CORRECT" != "y" ] read -p "Enter your name: " NAME read -p "Is ${NAME} correct? " CORRECT done LinuxTrainingAcademy.com Output - Checking User Input Enter your name: Luke Skywalker Is Luke Skywalker correct? n Enter your name: Jason Is Jason correct? y LinuxTrainingAcademy.com Example - Return Code of Command while ping -c app1 >/dev/null echo "app1 still up " sleep done echo "app1 down, continuing." LinuxTrainingAcademy.com Output - Return Code of Command app1 app1 app1 app1 app1 app1 still still still still still down, up up up up up continuing LinuxTrainingAcademy.com Reading a file, line-by-line LINE_NUM=1 while read LINE echo "${LINE_NUM}: ${LINE}" ((LINE_NUM++)) done < /etc/fstab LinuxTrainingAcademy.com Output - Reading a file, line-by-line 1: 2: 3: 4: 5: # /etc/fstab # /dev/mapper/centos-root / xfs LABEL=boot /boot xfs /dev/mapper/centos-swap swap swap defaults defaults defaults 1 0 LinuxTrainingAcademy.com Reading a file, line-by-line grep xfs /etc/fstab | while read LINE echo "xfs: ${LINE}" done LinuxTrainingAcademy.com Output - Reading a file, line-by-line xfs: /dev/mapper/centos-root / xfs: LABEL=boot /boot xfs xfs defaults defaults 1 LinuxTrainingAcademy.com FS_NUM=1 grep xfs /etc/fstab | while read FS MP REST echo "${FS_NUM}: file system: ${FS}" echo "${FS_NUM}: mount point: ${MP}" ((FS_NUM++)) done LinuxTrainingAcademy.com 1: 1: 2: 2: file system: mount point: file system: mount point: /dev/mapper/centos-root / LABEL=boot /boot LinuxTrainingAcademy.com while [ true ] read -p "1: Show disk usage 2: Show uptime " CHOICE case "$CHOICE" in 1) df -h ;; 2) uptime ;; *) break ;; esac done LinuxTrainingAcademy.com mysql -BNe 'show databases' | while read DB db-backed-up-recently $DB if [ "$?" -eq "0" ] then continue fi backup $DB done LinuxTrainingAcademy.com Summary ● ● ● While loops Infinite loops Loop control ○ ○ ○ ● ● Explicit number of times User input Command exit status Reading files, line-by-line break and continue LinuxTrainingAcademy.com ... command N done LinuxTrainingAcademy.com Infinite Loops while [ CONDITION_IS_TRUE ] # Commands NOT change # the condition command N done LinuxTrainingAcademy.com Infinite Loops while [ true ] command... ● ● ● While loops Infinite loops Loop control ○ ○ ○ ● ● Explicit number of times User input Command exit status Reading files, line-by-line break and continue LinuxTrainingAcademy.com While Loop... 'show databases' | while read DB db-backed-up-recently $DB if [ "$?" -eq "0" ] then continue fi backup $DB done LinuxTrainingAcademy.com Summary ● ● ● While loops Infinite loops Loop control