Bash functional: Difference between revisions
From wikinotes
(→Map) |
(→Filter) |
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= Filter = | = Filter = | ||
<blockquote> | <blockquote> | ||
< | <syntaxhighlight lang="bash"> | ||
# | # Call callable/params($*), passing each each STDIN line as the last parameter | ||
# | |||
# EXAMPLE: | |||
# divisible_by_2() { [ $(($1 % 2)) -eq 0 ] } | |||
# echo {1..10} | tr ' ' '\n' | map divisible_by_2 | |||
</ | # #> 2 | ||
# #> 4 | |||
# #> ... | |||
# | |||
filter() { | |||
local input | |||
while read -r input; do | |||
if "$@" "${input}" 2>&1 > /dev/null ; | |||
echo "${input}" | |||
fi | |||
done | |||
} | |||
</syntaxhighlight> | |||
</blockquote><!-- Filter --> | </blockquote><!-- Filter --> | ||
Revision as of 19:40, 11 December 2022
Fancy loops that let you process things incrementally in a pipeline.
You'll almost never use these directly, but it might be inspiration for a more useful function.
Filter
# Call callable/params($*), passing each each STDIN line as the last parameter # # EXAMPLE: # divisible_by_2() { [ $(($1 % 2)) -eq 0 ] } # echo {1..10} | tr ' ' '\n' | map divisible_by_2 # #> 2 # #> 4 # #> ... # filter() { local input while read -r input; do if "$@" "${input}" 2>&1 > /dev/null ; echo "${input}" fi done }
Map
NOTE:
If your callable accepts parameter as stdin, you don't need map (ex. grep/sed work just fine from stdin).
# Call callable/params($*), passing each each STDIN line as the last parameter # # EXAMPLE: # divisible_by_2() { # [ $(($1 % 2)) -eq 0 ] && echo "$1:yes" || echo "$1:no" # } # echo {1..10} | tr ' ' '\n' | map divisible_by_2 # #> 1:no # #> 2:yes # #> ... # map() { local input while read -r input; do "$@" "${input}" done }
Reduce
# callable/params must accept aggregate as 2nd-last param, and input as last param. # # EXAMPLE: # sum() { echo $(($1 + $2)) } # echo {1..10} | tr ' ' '\n' | reduce sum 0 # #> 55 # reduce() { local callable="${@:1:-1}" # all until last param local aggregate="${@[-1]}" # last param local input while read -r input; do aggregate="$("${callable[@]}" "${aggregate}" "${input}")" done echo "${aggregate}" }