shell

bash IFS

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Updated: 07 March 2024

Explode a string about a comma character, using the Internal Field Separator variable

mystr=foo,bar,spam

IFS=',' read -ra frags <<< $mystr
for frag in "${frags[@]}"; do
  echo "$frag"
done

# output
foo
bar
spam

zsh

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Updated: 17 June 2023

Files added by new install

.zshenv
.zprofile
.zshrc
.zlogin
.histfile

bash history

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Updated: 15 April 2023

History doesn’t get written to .bash_history until log off.

Show history

history

Clear session history

history -c

Delete item 234 from history

history -d 234

Writes all current session command history to the HISTFILE

history -w

Search history

Ctrl+R and start typing the previous command. Once a result appears, repeat Ctrl+R to see other matches. Enter to run command.

To re-run a command from history

!<item number>

bash process substitution

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Updated: 11 January 2023 

>(command_list)
<(command_list)

Process substitution feeds the output of a process (or processes) into the stdin of another process. It uses /dev/fd/<n> files to send the results of the process(es) within parentheses to another process. Effectively, process substitution turns a command into a temporary file, which is removed when the command completes.

cat <(echo hello world) # hello world
echo <(echo hello world) # /dev/fd/63

The first command converts the output of echo hello world into a file with contents hello world. The second command shows us the temp file in use.

The diff command requires files as arguments. So, comparing the contents of two directories can be achieved with diff and process substitution

diff <(ls /bin) <(ls /usr/bin)

Argbash

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Updated: 10 January 2023

https://argbash.dev/

Create an argbash template file

argbash-init --pos positional-arg --opt optional-arg minimal.m4

Use the template file to create a script

argbash minimal.m4 -o my-script.sh

Re-generate script after editing Argbash section

argbash my-script.sh -o my-script.sh

bash sort

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Updated: 04 March 2024

Sort by second column of tabulated data

$ printf "101\tc\n102\tb\n103\ta\n"
101	c
102	b
103	a

$ printf "101\tc\n102\tb\n103\ta\n" | sort -k2
103	a
102	b
101	c