UNIX related tutorial/FAQ

Bash check if string starts with character such as #

last updated December 14, 2018 in BASH Shell, Linux, UNIX

My bash shell script read a config file line-by-line using a bash while loop. I need to check if a string stored in $var starts with some value such as # character. If so I need to ignore that value and read the next line from my config file. How do I check if variable begins with # in bash shell scripting running on a Linux or Unix-like operating systems?

Bash get exit code of command on a Linux / Unix

last updated December 4, 2018 in BASH Shell, Linux, UNIX

I am a new Linux system user. How do I get the exit code of a command? How do I get the exit code of Linux or Unix shell command and store it into a shell variable?

Bash read file names from a text file and take action

last updated December 3, 2018 in BASH Shell, Linux, Programming, UNIX

I need to read a list of file names from a text file named input.txt and take action each file name. How do I read file names from a text file and say run /bin/foo command on each file? How do I read filenames from a text file and take certain action on those files?

Define ssh key per host using ansible_ssh_private_key_file

last updated November 30, 2018 in Linux, UNIX

I set up SSH keys on a Linux or Unix as per my project needs and cloud hosting providers. I also new to Ansible IT automation and DevOps tool. My management node has keys for Linode, AWS/EC2 and Google cloud. How do I set up and tell Ansible to use different ssh keys? How do I configure SSH credentials per cloud hosting service provider?

Bash foreach loop examples for Linux / Unix

last updated November 19, 2018 in BASH Shell, Linux, UNIX

I used foreach on a Unix operating system and csh shell loop. Now, I am a Linux operating system. How do I use foreach loop in bash shell running on Linux?

Bash check if process is running or not on Linux / Unix

last updated November 17, 2018 in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, UNIX

I am new to Linux shell scripting. I am using a CentOS 7 Linux and Ubuntu 18.04 LTS server in the cloud. How do I check if a process is running or not on Linux? How do I determine whether a process is running or not in a shell script running on an Ubuntu server?

Ansible reboot Linux machine or server with playbooks

last updated October 6, 2018 in CentOS, Debian / Ubuntu, FreeBSD, Linux, OpenBSD, RedHat and Friends, Suse, UNIX

I need to reboot the VM or bare metal Linux machine/server using Ansible and wait for it to come back, but it does not work with playbook as descried here. How to reboot Linux server with Ansible? How do I reboot and wait for reboot to complete in Ansible playbook for multiple Linux servers?

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