Check if a program exists from a Makefile

问题:

How can I check if a program is callable from a Makefile?

(That is, the program should exist in the path or otherwise be callable.)

It could be used to check for which compiler is installed, for instance.

E.g. something like this question, but without assuming the underlying shell is POSIX compatible.

回答1:

Sometimes you need a Makefile to be able to run on different target OS's and you want the build to fail early if a required executable is not in PATH rather than to run for a possibly long time before failing.

The excellent solution provided by engineerchuan requires making a target. However, if you have many executables to test and your Makefile has many independent targets, each of which requires the tests, then each target requires the test target as a dependency. That makes for a lot of extra typing as well as processing time when you make more than one target at a time.

The solution provided by 0xf can test for an executable without making a target. That saves a lot of typing and execution time when there are multiple targets that can be built either separately or together.

My improvement to the latter solution is to use the which executable (where in Windows), rather than to rely on there being a --version option in each executable, directly in the GNU Make ifeq directive, rather than to define a new variable, and to use the GNU Make error function to stop the build if a required executable is not in ${PATH}. For example, to test for the lzop executable:

 ifeq (, $(shell which lzop))
 $(error "No lzop in $(PATH), consider doing apt-get install lzop")
 endif

If you have several executables to check, then you might want to use a foreach function with the which executable:

EXECUTABLES = ls dd dudu lxop
K := $(foreach exec,$(EXECUTABLES),\
        $(if $(shell which $(exec)),some string,$(error "No $(exec) in PATH")))

Note the use of the := assignment operator that is required in order to force immediate evaluation of the RHS expression. If your Makefile changes the PATH, then instead of the last line above you will need:

        $(if $(shell PATH=$(PATH) which $(exec)),some string,$(error "No $(exec) in PATH")))

This should give you output similar to:

ads$ make
Makefile:5: *** "No dudu in PATH.  Stop.

回答2:

I mixed the solutions from @kenorb and @0xF and got this:

DOT := $(shell command -v dot 2> /dev/null)

all:
ifndef DOT
    $(error "dot is not available please install graphviz")
endif
    dot -Tpdf -o pres.pdf pres.dot 

It works beautifully because "command -v" doesn't print anything if the executable is not available, so the variable DOT never gets defined and you can just check it whenever you want in your code. In this example I'm throwing an error, but you could do something more useful if you wanted.

If the variable is available, "command -v" performs the inexpensive operation of printing the command path, defining the DOT variable.

回答3:

is this what you did?

check: PYTHON-exists
PYTHON-exists: ; @which python > /dev/null
mytarget: check
.PHONY: check PYTHON-exists

credit to my coworker.

回答4:

Use the shell function to call your program in a way that it prints something to standard output. For example, pass --version.

GNU Make ignores the exit status of the command passed to shell. To avoid the potential "command not found" message, redirect standard error to /dev/null.

Then you may check the result using ifdef, ifndef, $(if) etc.

YOUR_PROGRAM_VERSION := $(shell your_program --version 2>/dev/null)

all:
ifdef YOUR_PROGRAM_VERSION
    @echo "Found version $(YOUR_PROGRAM_VERSION)"
else
    @echo Not found
endif

As a bonus, the output (such as program version) might be useful in other parts of your Makefile.

回答5:

My solution involves a little helper script¹ that places a flag file if all required commands exist. This comes with the advantage that the check for the required commands is only done once and not on every make invocation.

check_cmds.sh

#!/bin/bash

NEEDED_COMMANDS="jlex byaccj ant javac"

for cmd in ${NEEDED_COMMANDS} ; do
    if ! command -v ${cmd} &> /dev/null ; then
        echo Please install ${cmd}!
        exit 1
    fi
done

touch .cmd_ok

Makefile

.cmd_ok:
    ./check_cmds.sh

build: .cmd_ok target1 target2

¹ More about the command -v technique can be found here.

回答6:

Cleaned up some of the existing solutions here...

REQUIRED_BINS := composer npm node php npm-shrinkwrap
$(foreach bin,$(REQUIRED_BINS),\
    $(if $(shell command -v $(bin) 2> /dev/null),$(info Found `$(bin)`),$(error Please install `$(bin)`)))

The $(info ...) you can exclude if you want this to be quieter.

This will fail fast. No target required.

回答7:

For me all above answers are based on linux and are not working with windows. I'm new to make so my approach may not be ideal. But complete example that works for me on both linux and windows is this:

# detect what shell is used
ifeq ($(findstring cmd.exe,$(SHELL)),cmd.exe)
$(info "shell Windows cmd.exe")
DEVNUL := NUL
WHICH := where
else
$(info "shell Bash")
DEVNUL := /dev/null
WHICH := which
endif

# detect platform independently if gcc is installed
ifeq ($(shell ${WHICH} gcc 2>${DEVNUL}),)
$(error "gcc is not in your system PATH")
else
$(info "gcc found")
endif

optionally when I need to detect more tools I can use:

EXECUTABLES = ls dd 
K := $(foreach myTestCommand,$(EXECUTABLES),\
        $(if $(shell ${WHICH} $(myTestCommand) 2>${DEVNUL} ),\
            $(myTestCommand) found,\
            $(error "No $(myTestCommand) in PATH)))
$(info ${K})        

回答8:

You can use bash built commands such as type foo or command -v foo, as below:

SHELL := /bin/bash
all: check

check:
        @type foo

Where foo is your program/command. Redirect to > /dev/null if you want it silent.

回答9:

Solved by compiling a special little program in another makefile target, whose sole purpose is to check for whatever runtime stuff I was looking for.

Then, I called this program in yet another makefile target.

It was something like this if I recall correctly:

real: checker real.c
    cc -o real real.c `./checker`

checker: checker.c
    cc -o checker checker.c

回答10:

Assume you have different targets and builders, each requires another set of tools. Set a list of such tools and consider them as target to force checking their availability

For example:

make_tools := gcc md5sum gzip

$(make_tools):  
    @which $@ > /dev/null

file.txt.gz: file.txt gzip
    gzip -c file.txt > file.txt.gz