在我的shell程序中获取C程序的返回码

Question

Suppose I have a C program named Foo.c which is printing few things and returning a value named rc which I am executing in my shell program as follows :

foobar=$(Foo | tail -1)

Now, the variable foobar has the last printed value of the program Foo . But without disturbing this, I want to get the return code rc of the program in my shell program.

Answer 1

If you are using bash shell, you can use PIPESTATUS array variable to get the status of the pipe process.

$ tail sat | wc -l
tail: cannot open ‘sat’ for reading: No such file or directory
0
$ echo "${PIPESTATUS[0]} ${PIPESTATUS[1]}"
1 0
$

From man bash :

PIPESTATUS

An array variable containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command).

Answer 2

You can use "set -o pipefail" option.

[root@myserver Test]# set -o pipefail
[root@myserver Test]# ./a.out | tail -l
[root@myserver Test]# echo $?
100

Here my program a.out returns 100.

Or another options is to use pipestatus environment variable. You can read about it here. http://www.linuxnix.com/2011/03/pipestatus-internal-variable.html

Answer 3

This assigns the last line of the output of Foo to foobar and Foo's exit code is assigned to code :

{ read -r foobar; read code; } < <( (Foo; echo $? ) | tail -2)

The <(...) construct is called process substitution . In the code above, the read commands receive their stdin from the process substitution. Because of the tail -2 , the process substitution produces a total of two lines. The first line is the last line produced by Foo and it is assigned to foobar . The second is assigned to code .

The space between the first and second < is essential.

Example

After creating a function Foo, the above can be tested:

$ Foo() { echo "Testing"; false; }
$ { read -r foobar; read code; } < <( (echo "Testing"; false; echo $? ) | tail -2)
$ echo "foobar=$foobar code=$code"
foobar=Testing code=1

And:

$ Foo() { echo "2nd Test"; true; }
$ { read -r foobar; read code; } < <( (Foo; echo $? ) | tail -2)
$ echo "foobar=$foobar code=$code"
foobar=2nd Test code=0

Answer 4

I'm afraid that you have to use a temporal file to store the output of the Foo program, get the return code and then perform the tail -1. Just like the following:

Foo > /tmp/temp_file
ret=$?
foobar=$(tail -1 /tmp/temp_file)

Answer 5

$? gives the return value of the last executed command.