Bash functional: Difference between revisions
From wikinotes
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Revision as of 19:32, 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
# filters out results not matching 'grep foo' find . \ | while read line; do \ echo $line | grep foo && echo "$line"; \ 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 "$2:no" # } # # echo {1..4} | tr ' ' '\n' | map divisible_by_2 # # #> 1:no # #> 2:yes # #> 3:no # #> 4:yes # map() { local input while read -r input; do "$@" "${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}" }