Misc

• There’s a great little primer on how to run scripts here.
• There are lots of scripts in my infra-scripts repo (only available to Clare).
  • Note that this also contains a file called useful-aliases.txt - if I want the most up to date versions of these functions (eg wp), I need to copy its contents into ~/.bashrc.
  • But they were all written for Windows, so you’ll need to do a search and replace on file paths for both Clare home and the development directory.
  • Also sometiumes you might get weird errors caused by WIndows line endings (eg “command not found” for an empty line), in which case you need to run dos2unix on your scripts (search elsewhere in this wiki for info on dos2unix)
• Sample bash script: Dropbox\IT Training\Misc\sample.bashrc
• if statement - the spaces matter! if [[ $NumDifferences != 0 ]]; then … fi
• Bash scripts:
  • set -x - also works on the command line - outputs every command that’s run to the command shell - include nested commands - useful for debugging (output all)
    • set -e - stops running on any error (also works on the command line)
  • If you include this line at the top of your script, it means you don’t have to use the “sh” command when you run the script on the command line:
    • This: #!/usr/bin/env bash
      • People normally use this - #!/bin/bash - but the above is better. Explanation here.
    • You also have to do this: chmod +x /path/to/script
  • You don’t have to give your script an extension
    • So for instance if you just call it winpath instead of winpath.sh, and you have it in your path, then you can run it as a winpath command from anywhere.
    • This is preferable to adding functions to your bashrc file.
    • If you want to run your script from anywhere on your system, see Installing scripts
• There are more useful Bash links in my Chrome bookmarks: Useful - Coding Languages and Tech - Bash Scripts

Troubleshooting Git Bash

Where is the root of the git Bash terminal?

• When you run Git Bash your command prompt is always at /, which is the root for Git Bash but is not the root of your machine (in windows 10)
• The way to find out where it is is to run explorer . in the terminal
• That will open a File Explorer at the location
• It is generally at C:\Program Files\Git\
• So for instance, what’s shown as /usr/bin in Git Bash is actually at C:\Program Files\Git\usr\bin

Fails to run

• If you get an error “Failed to run ‘/usr/bin/bash’: No such file or directory”
  • Avast sometimes quarantines bash.exe
  • In Avast, go to Protection (on the left), then select Quarantine
  • Find bash.exe
  • Select the file
  • click the dots at the bottom
  • select “restore and add exception”
  • More here
• You can report a false positive here
• More here

Bash variables

• Lack of spaces is important when assigning to variables!

  • Like this: File=$1
  • You get a “command not found” error when you have spaces between the variable declaration and the = sign. More on that here.
  • Using variables

• From find-changed-chef-nagios-nodes.sh (in observability-toolbox):

  • Take a command line result and put it into a Bash variable (gives you an int): OldNodes=`wc -l < old-chef-results.txt`

    • You need the -l because otherwise you get text, not a number

    • Another way of doing the same - gives you a string but I don’t know if that’s the difference (from find-changed-single-chef-node.sh):

      • new_data=$(echo $chef_search_result | grep -o -P ‘.datacenter.{0,78}’)

  • Assign vars and do maths in Bash: let NodeDiff=$NewNodes-$OldNodes

  • Building a file name with timestamp: Lines 38 onwards in find-changed-chef-nagios-nodes.sh (in observability-toolbox)

• From find-changed-single-chef-node.sh:

  • Turn parameter into a file name: file=”$1”

  • Echo a variable to the command line: echo -n $(date) | tee -a changed-single-node.txt

    • I think -n is important but I can’t remember why

variable expansion syntax

• If you type

  • clare/{big,small}/thing

  • it will be converted to

  • clare/big/thing clare/small/thing

• Useful use case:

  • git mv clare/{big,small}/thing

  • will translate to

  • git mv clare/big/thing clare/small/thing

• Also you can do this:

  • git mv clare/thing.txt{,.erb}

  • will be converted to

  • git mv clare/thing.txt clare/thing.txt.erb