Bash Code Diary Entries

This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job.

• Bash profile vs bashrc vs profile
• Be careful not to clobber existing traps
• Clis do not use commas between entries
• Comments are invalid in multi line bash commands
• Consider the effect on your argument numbers when a variable may not be set
• Deploy scripts must be idempotent and deleting existing code folder is the simplest way to achieve this
• Do not forget semicolons when running sh c
• ENV variables are strings
• Exiting from a subshell does not end your shell script
• Here string in shell
• How to check if a program is available
• How to check if a shell script received any arguments
• How to control flow based on booleanish variables in bash scripts
• How to convert unix timestamp to human readable on command line
• How to do arithmetic in bash
• How to do math on the command line
• How to dry up repeated flags in bash scripts using wrapper functions
• How to get a remote REPL to read from STDIN pipe
• How to get past developer cannot be identified restrictions on command line
• How to iterate through numbers in bash
• How to keep retrying some code until it works
• How to parallelize a loop
• How to remove first n digits in bash with string substitution
• How to rename many files with string substitution
• How to turn many lines into one line
• How to use 100 percent CPU on all cores
• Leading 0s cause bash to interpret numbers in the wrong base
• List all available commands
• Numbers following interpolated variables need to be in separate strings
• One liner for setting exit code to numbers under your control
• Remove a single sensitive entry from history
• Scripting basics
• Shell commands in loops compete for STDIN in unpredictable ways
• Shorthand to get the last argument of the previous command
• Show errors codes on screen always
• Simple redirecting can include too much
• Some err traps are skipped with set e
• The outermost string must have double quotes for string substitution to work in nested single quote strings
• Trap ERR vs trap EXIT
• Understand redirection
• Understand why colors disappear with pipes
• Up your pipe game with the echo and command substitution trick
• Use a heredoc to execute many commands remotely
• Use arrays instead of strings for building up bash argument lists to pass to other commands
• Use non interactive flags in scripts
• Use redirection to stop programs printing out filenames in their output
• Ways of iterating in bash
• What does the set command do
• Wildcard ignores hidden files
• Worked example of a subshell
• Write out full flags in reused code
• You can append with redirection as well as overwrite a file
• You cannot connect STDIN to interactive processes