Handling signals from within Bash has a simple syntax and can be used to handle user interruption with Ctrl-C (SIGINT), as a cleanup hook at the end of processing (SIGEXIT), or even as a custom messaging mechanism (SIGUSR1). Trapping a signal is as easy as specifying a custom function name and the signal name as … Bash: trapping signals during script processing
One of the features of the ‘lineinfile‘ regexp parameter is the ability to use regular expression capture groups in the line output. That allows you to extract values on a found line when constructing the output line. Specifically, that can mean pulling information such as hostname/port, file path, or preserving the yaml indentation of an … Ansible: regex capture groups with lineinfile to preserve yaml indentation
sed is a powerful utility for transforming text. One of the nice tricks with sed is the ability to reuse capture groups from the source string in the replacement value you are constructing. For example, if you have have the following kernel parameters in “/etc/default/grub” $ grep GRUB_CMDLINE_LINUX_DEFAULT /etc/default/grub GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash” And wanted to append … Bash: Appending to existing values using sed capture group
The =~ binary operator provides the ability to compare a string to a POSIX extended regular expression in the shell. Take note, the right-hand side regex cannot be surrounded by quotes or it will be treated as a regular string, it cannot contain spaces, and must conform to POSIX regex rules and use character classes … Bash: Using BASH_REMATCH to pull capture groups from a regex
For troubleshooting deep rooted network issues, you may be accustomed to using tcpdump against a network interface on Linux. This same utility can be used on OpenWrt to troubleshoot network issues. The Opkg Package manager makes this easy to install.
The prevalence of the long chains of firewall and reverse proxy solutions present in production infrastructure (and made even more popular with the dynamic routing introduced with containers) has made analysis of the end-user side of the network exchange a critical tool in troubleshooting. Fiddler has long been a solid tool for both proxy capture … Ubuntu: Using Fiddler to analyze Chrome/Firefox network capture