Variable

Single Value ​

Basic variable usage ​

Creating variables:

set var_name value
read my_name

Using variables:

echo $HOME
echo {$WORD}s
echo "$foo $bar"

Compare datetime ​

To easily compare date and time in fish, we remove / and : to make them become numbers, and then use test to compare.

function check_time --argument-names now # now is in format HH:MM
    set now (echo "$now" | tr -d :)
    if test "$now" -lt 0600
        echo 'You should be sleeping now!'
    else if test "$now" -lt 1200
        echo 'Good morning!'
    else if test "$now" -lt 1800
        echo 'Good day!'
    else
        echo 'Good night!'
    end
end

Save command output ​

Save the output of a command in a variable and use it later (possibly several times to avoid running the command every time):

ps -ef | read --null ps_output
printf '%s' $ps_output | sed -nE 's#pattern#\1#p'

Array ​

Basic array usage ​

Creating an array:

set fruits banana orange melon

Fish uses base 1 for accessing values in a list.

echo $fruits[1]  # => banana

Use negative index to access from the end.

echo $fruits[-1]  # => melon

Get a slice with the .. syntax (left/right defaults: 1..-1)

echo $fruits[..-2]  # => banana orange

Escape and expand arrays ​

Print an array with every element quoted with ' (useful if we need to expand it inside " for another command):

echo "'$(string join "' '" $fruits)'" # => 'banana' 'orange' 'melon'

If outside double quotes, the same can achieved with:

echo \'$fruits\' # => 'banana' 'orange' 'melon'

The same syntax can be used to expand multiple arguments:

set options --arg=$fruits # => --arg=banana --arg=orange --arg=melon

Integrate arrays with commands ​

Output of commands can be splitted on newlines if using command substitution:

set lines (cmd)

To pipe an array to a command, make each element be in one line:

string join \n $fruits | cmd
printf '%s\n' $fruits | cmd

With this we can, for example, sort the elements of an array:

set fruits (string join \n $fruits | sort)

Avoid cat ​

To avoid running cat and creating a new process just to print the contents of a file, use fish's builtin read instead.

# Instead of
set lines (cat input_file)
# Do
set lines (read --null <input_file)

Special variables ​

Load environment file ​

Considering .env an environment file (with KEY=VALUE tuples), one can export those variables in fish using:

export (xargs -L 1 <.env)

Or a more complex solution like:

export (grep -E '^[^#;].+=.*' .env | xargs -L 1)