makefile hangs when calling shell command head

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I want to print the first line of some text file from within my makefile.
Here's what I have, and it doesn't seem to work:

$ cat makefile

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

all:

    var=${MYDIR}/m.txt

    @echo $(shell head -n 1 ${var})

#   @echo $(shell head -n 1 ${MYDIR}/m.txt)

When I try to use make it simply hangs and I have to kill it.
When I remove the comment and use the head command directly on ${MYDIR}/m.txt everything works fine. What am I doing wrong here? Thanks!

asked Jan 3 at 12:00

OrenIshShalom

1,158924

Tangentially, don't use @ to silence make, especially while debugging. Once you know exactly what's going on, you probably want to use make -s if you don't want to see what's happening.

– tripleee
Jan 3 at 12:55

I prefer this method of dealing with recipe echoing: make.mad-scientist.net/managing-recipe-echoing

– MadScientist
Jan 3 at 14:53

add a comment |

I want to print the first line of some text file from within my makefile.
Here's what I have, and it doesn't seem to work:

$ cat makefile

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

all:

    var=${MYDIR}/m.txt

    @echo $(shell head -n 1 ${var})

#   @echo $(shell head -n 1 ${MYDIR}/m.txt)

asked Jan 3 at 12:00

OrenIshShalom

1,158924

Tangentially, don't use @ to silence make, especially while debugging. Once you know exactly what's going on, you probably want to use make -s if you don't want to see what's happening.

– tripleee
Jan 3 at 12:55

I prefer this method of dealing with recipe echoing: make.mad-scientist.net/managing-recipe-echoing

– MadScientist
Jan 3 at 14:53

add a comment |

I want to print the first line of some text file from within my makefile.
Here's what I have, and it doesn't seem to work:

$ cat makefile

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

all:

    var=${MYDIR}/m.txt

    @echo $(shell head -n 1 ${var})

#   @echo $(shell head -n 1 ${MYDIR}/m.txt)

asked Jan 3 at 12:00

OrenIshShalom

1,158924

I want to print the first line of some text file from within my makefile.
Here's what I have, and it doesn't seem to work:

$ cat makefile

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

all:

    var=${MYDIR}/m.txt

    @echo $(shell head -n 1 ${var})

#   @echo $(shell head -n 1 ${MYDIR}/m.txt)

bash makefile

asked Jan 3 at 12:00

OrenIshShalom

1,158924

asked Jan 3 at 12:00

OrenIshShalom

1,158924

asked Jan 3 at 12:00

OrenIshShalom

1,158924

asked Jan 3 at 12:00

OrenIshShalom

1,158924

asked Jan 3 at 12:00

OrenIshShalom

1,158924

Tangentially, don't use @ to silence make, especially while debugging. Once you know exactly what's going on, you probably want to use make -s if you don't want to see what's happening.

– tripleee
Jan 3 at 12:55

I prefer this method of dealing with recipe echoing: make.mad-scientist.net/managing-recipe-echoing

– MadScientist
Jan 3 at 14:53

add a comment |

Tangentially, don't use @ to silence make, especially while debugging. Once you know exactly what's going on, you probably want to use make -s if you don't want to see what's happening.

– tripleee
Jan 3 at 12:55

I prefer this method of dealing with recipe echoing: make.mad-scientist.net/managing-recipe-echoing

– MadScientist
Jan 3 at 14:53

Tangentially, don't use @ to silence make, especially while debugging. Once you know exactly what's going on, you probably want to use make -s if you don't want to see what's happening.

– tripleee
Jan 3 at 12:55

I prefer this method of dealing with recipe echoing: make.mad-scientist.net/managing-recipe-echoing

– MadScientist
Jan 3 at 14:53

add a comment |

2 Answers
2

active

oldest

votes

Do not use the shell make function in recipes. Recipes are already shell scripts:

BASEDIR := $(HOME)/Downloads

MYDIR   := $(BASEDIR)/ddd



all:

    @var="$(MYDIR)/m.txt"; head -n 1 "$$var"

Notes:

Recipes are expanded by make before they are passed to the shell. This is where $(MYDIR) will be replaced by something like /home/doe/Downloads/ddd/m.txt. And this is why $var would not work. It would expand as ar, unless there is a make variable named v with a non-empty value FOO, in which case $var would expand as FOOar. $$var is expanded by make as $var, the shell syntax you want.

Each line of a recipe is executed by an independent shell. The following would thus not work:
```
all:

    @var="$(MYDIR)/m.txt"

    @head -n 1 "$$var"
```
because the shell variable assignment (var="/home/doe/Downloads/ddd/m.txt") and the shell variable expansion (head -n 1 "$var") would be executed by two different shells. If you want one single shell statement per line, use the line continuation:
```
all:

    @var="$(MYDIR)/m.txt"; 

    head -n 1 "$$var"
```
or:
```
all:

    @var="$(MYDIR)/m.txt" && 

    head -n 1 "$$var"
```

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

1

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

1

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

add a comment |

Don't use variable assignments in recipes. In your command head -n 1 ${var} the expression ${var} expands to nothing and hence head waits on standard input. The following makefile should work:

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

var=${MYDIR}/m.txt

all:

    @echo $(shell head -n 1 ${var})

answered Jan 3 at 12:20

Leon

21.8k23372

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

Do not use the shell make function in recipes. Recipes are already shell scripts:

BASEDIR := $(HOME)/Downloads

MYDIR   := $(BASEDIR)/ddd



all:

    @var="$(MYDIR)/m.txt"; head -n 1 "$$var"

Notes:

Recipes are expanded by make before they are passed to the shell. This is where $(MYDIR) will be replaced by something like /home/doe/Downloads/ddd/m.txt. And this is why $var would not work. It would expand as ar, unless there is a make variable named v with a non-empty value FOO, in which case $var would expand as FOOar. $$var is expanded by make as $var, the shell syntax you want.

Each line of a recipe is executed by an independent shell. The following would thus not work:
```
all:

    @var="$(MYDIR)/m.txt"

    @head -n 1 "$$var"
```
because the shell variable assignment (var="/home/doe/Downloads/ddd/m.txt") and the shell variable expansion (head -n 1 "$var") would be executed by two different shells. If you want one single shell statement per line, use the line continuation:
```
all:

    @var="$(MYDIR)/m.txt"; 

    head -n 1 "$$var"
```
or:
```
all:

    @var="$(MYDIR)/m.txt" && 

    head -n 1 "$$var"
```

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

1

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

1

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

add a comment |

Do not use the shell make function in recipes. Recipes are already shell scripts:

BASEDIR := $(HOME)/Downloads

MYDIR   := $(BASEDIR)/ddd



all:

    @var="$(MYDIR)/m.txt"; head -n 1 "$$var"

Notes:

Recipes are expanded by make before they are passed to the shell. This is where $(MYDIR) will be replaced by something like /home/doe/Downloads/ddd/m.txt. And this is why $var would not work. It would expand as ar, unless there is a make variable named v with a non-empty value FOO, in which case $var would expand as FOOar. $$var is expanded by make as $var, the shell syntax you want.

Each line of a recipe is executed by an independent shell. The following would thus not work:
```
all:

    @var="$(MYDIR)/m.txt"

    @head -n 1 "$$var"
```
because the shell variable assignment (var="/home/doe/Downloads/ddd/m.txt") and the shell variable expansion (head -n 1 "$var") would be executed by two different shells. If you want one single shell statement per line, use the line continuation:
```
all:

    @var="$(MYDIR)/m.txt"; 

    head -n 1 "$$var"
```
or:
```
all:

    @var="$(MYDIR)/m.txt" && 

    head -n 1 "$$var"
```

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

1

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

1

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

add a comment |

Do not use the shell make function in recipes. Recipes are already shell scripts:

BASEDIR := $(HOME)/Downloads

MYDIR   := $(BASEDIR)/ddd



all:

    @var="$(MYDIR)/m.txt"; head -n 1 "$$var"

Notes:

Recipes are expanded by make before they are passed to the shell. This is where $(MYDIR) will be replaced by something like /home/doe/Downloads/ddd/m.txt. And this is why $var would not work. It would expand as ar, unless there is a make variable named v with a non-empty value FOO, in which case $var would expand as FOOar. $$var is expanded by make as $var, the shell syntax you want.

Each line of a recipe is executed by an independent shell. The following would thus not work:
```
all:

    @var="$(MYDIR)/m.txt"

    @head -n 1 "$$var"
```
because the shell variable assignment (var="/home/doe/Downloads/ddd/m.txt") and the shell variable expansion (head -n 1 "$var") would be executed by two different shells. If you want one single shell statement per line, use the line continuation:
```
all:

    @var="$(MYDIR)/m.txt"; 

    head -n 1 "$$var"
```
or:
```
all:

    @var="$(MYDIR)/m.txt" && 

    head -n 1 "$$var"
```

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

Do not use the shell make function in recipes. Recipes are already shell scripts:

BASEDIR := $(HOME)/Downloads

MYDIR   := $(BASEDIR)/ddd



all:

    @var="$(MYDIR)/m.txt"; head -n 1 "$$var"

Notes:

Recipes are expanded by make before they are passed to the shell. This is where $(MYDIR) will be replaced by something like /home/doe/Downloads/ddd/m.txt. And this is why $var would not work. It would expand as ar, unless there is a make variable named v with a non-empty value FOO, in which case $var would expand as FOOar. $$var is expanded by make as $var, the shell syntax you want.

Each line of a recipe is executed by an independent shell. The following would thus not work:
```
all:

    @var="$(MYDIR)/m.txt"

    @head -n 1 "$$var"
```
because the shell variable assignment (var="/home/doe/Downloads/ddd/m.txt") and the shell variable expansion (head -n 1 "$var") would be executed by two different shells. If you want one single shell statement per line, use the line continuation:
```
all:

    @var="$(MYDIR)/m.txt"; 

    head -n 1 "$$var"
```
or:
```
all:

    @var="$(MYDIR)/m.txt" && 

    head -n 1 "$$var"
```

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

edited Jan 3 at 13:03

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

answered Jan 3 at 12:48

Renaud Pacalet

9,69821732

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

1

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

1

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

add a comment |

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

1

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

1

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

It is of course dubious whether putting the string in a variable and only using it once is any use at all, but I'll just leave this comment here. (^8

– tripleee
Jan 3 at 13:01

@tripleee: agreed. But I suspect the real Makefile will be different, at the end. So, let's show how to properly use shell variables in make recipes, it is always good to know.

– Renaud Pacalet
Jan 3 at 13:02

how come I can't extend the solution to: `x=$(head -n 1 "$$var"); echo $$x'

– OrenIshShalom
Jan 3 at 19:45

@OrenIshShalom: you can... if you properly escape all $ signs: x=$$(head -n 1 "$$var"); echo "$$x".

– Renaud Pacalet
Jan 4 at 0:48

add a comment |

Don't use variable assignments in recipes. In your command head -n 1 ${var} the expression ${var} expands to nothing and hence head waits on standard input. The following makefile should work:

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

var=${MYDIR}/m.txt

all:

    @echo $(shell head -n 1 ${var})

answered Jan 3 at 12:20

Leon

21.8k23372

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

add a comment |

Don't use variable assignments in recipes. In your command head -n 1 ${var} the expression ${var} expands to nothing and hence head waits on standard input. The following makefile should work:

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

var=${MYDIR}/m.txt

all:

    @echo $(shell head -n 1 ${var})

answered Jan 3 at 12:20

Leon

21.8k23372

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

add a comment |

Don't use variable assignments in recipes. In your command head -n 1 ${var} the expression ${var} expands to nothing and hence head waits on standard input. The following makefile should work:

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

var=${MYDIR}/m.txt

all:

    @echo $(shell head -n 1 ${var})

answered Jan 3 at 12:20

Leon

21.8k23372

Don't use variable assignments in recipes. In your command head -n 1 ${var} the expression ${var} expands to nothing and hence head waits on standard input. The following makefile should work:

BASEDIR = ${HOME}/Downloads

MYDIR = ${BASEDIR}/ddd

var=${MYDIR}/m.txt

all:

    @echo $(shell head -n 1 ${var})

answered Jan 3 at 12:20

Leon

21.8k23372

answered Jan 3 at 12:20

Leon

21.8k23372

answered Jan 3 at 12:20

Leon

21.8k23372

answered Jan 3 at 12:20

Leon

21.8k23372

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

add a comment |

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

You still want to avoid using $(shell) in the recipe. The echo is also useless.

– tripleee
Jan 3 at 12:56

add a comment |

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