Fish Shell:
Deleting characters matching a pattern

How to:

# Remove digits from a string
set string "Fish123Shell"
echo $string | string replace -ra '[0-9]' ''
# Outputs: FishShell

# Strip out everything but lowercase letters
set noisy_string "F!i@s#h$%S^h&e*l(l)__+"
echo $noisy_string | string match -r '[a-z]+'
# Outputs: ishhell

Deep Dive

In Fish Shell, the magic happens with the string utility, a handy built-in tool for string operations - introduced in version 2.3.0. Prior to this, users would fall back on UNIX staples like sed or awk. Why the change? Simplicity and integration. Having an in-house solution streamlines string manipulation, making scripts more readable and maintainable.

Alternatives? Sure, the old guard sed can still do the job:

set old_school_string "Fish@Shell2023"
echo $old_school_string | sed 's/[0-9]//g'
# Outputs: Fish@Shell

But why not leverage Fish’s own tools? For implementation, string replace has a -r option enabling regex patterns. -a applies the command to all matches, and adding a ’’ at the end tells it to replace with nothing, i.e., delete. Use string match when searching for a pattern to keep, instead of what to ditch.

See Also

• Official Fish Shell Documentation on string: https://fishshell.com/docs/current/cmds/string.html
• Regex tutorial for deep diving into patterns: https://www.regular-expressions.info/
• Sed & Awk, age-old text powers: an intro: https://www.gnu.org/software/sed/manual/sed.html, http://www.grymoire.com/Unix/Awk.html