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Upgrading/Using bash on macOS

The word on the street is that macOS Catalina will switch to using zsh instead of bash as the default shell. If you use bash as your default shell and plan to upgrade to Catalina, this change will probably break some things for you in weird ways. Regardless of that, though, the version of bash that ships with macOS is very old and should probably be updated anyway.

One way to get a current version of bash on macOS is to install via Homebrew:

brew install bash

However you prefer to get bash is up to you. However, the next two steps are the same regardless -

Now, to use this version of bash (or any other shell, for that matter), you need to add the path of the shell to the list of "allowed" shells:

sudo bash -c 'echo /usr/local/bin/bash >> /etc/shells'

Next, you need to change your shell to use your version of bash:

chsh -s /usr/local/bin/bash

References:

Cheat Sheets

https://gist.github.com/JoshuaEstes/2627607#file-bash-cheat-sheet-md

Redirect stderr to stdout

Use the command as follows:

some-command 2>&1

Or:

some-command > myfile.txt 2>&1

Redirect stdout to stderr

Use the command as follows:

echo "Hello, World" 1>&2
echo "Hello, World" >&2

The second form is short-hand for the first.

See here for more details.

Loops

Use for combined with seq to implement a C-style for loop:

for i in `seq 0 9`; do echo $i; done

And you can do fun stuff like this:

for i in `seq -f "%02g" 99 -1 0`; do echo "$i bottles of beer on the wall"; done

Excluding Lines of Output

Use awk to omit the first N rows. For example:

ls -l | awk '{ if (NR > 1) print }'