makefile - One child process per for loop in make? -

let me first write quick makefile showcase:

#!/bin/make -f  folders := $(shell find -mindepth 1 -maxdepth 1 -type d -print)  make_dir:     @mkdir -p "test0"  pwd_test:     @cd "test0" && pwd     @pwd  pwd_all:     @for f in $(folders); \         cd "$${f}" && pwd; \         pwd; \         cd ..; \     done 

first make make_dir , see different results:

➜   make pwd_test /data/cache/tmp/so/test0 /data/cache/tmp/so ➜   make pwd_all  /data/cache/tmp/so/test0 /data/cache/tmp/so/test0 

you see in loop necessary cd ... apparently, there no child process spawn cd x && pwd command, while case. behaviour specific make or specific shell?

make spawns new process each command in rule. since loop 1 command 1 process.

take @ recipe execution

edit:

each line in makefile gets own subshell. commands have \ tells make next line should part of current line.

the reason loop own subshell because make see line

@for f in $(folders); cd "$${f}" && pwd; pwd; cd ..; done 

madscientist explains well. command can type in shell in 1 line executed make in 1 subshell or process.

if run in ksh, ksh passed for f in $(folders); cd "$${f}" && pwd; pwd; cd ..; done , run in 1 subshell. if ksh did not have loop implemented error , make command returned error code.

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explanation of pwd_test

pwd_test:     @cd "test0" && pwd     @pwd 

@cd "test0" && pwd seen 1 line subshell updates current working directory , prints out current working is.

@pwd @ line make spawns new subshell contains old working directory (or directory make called form) , pwd prints directory.