Bash – Execute two commands and get exit status 1 if first fails

bashexit-status

In the case below, the report command must always be executed but I need to get an exit status 1 if the test command fails:

test;report
echo $?
0

How can I do it in a single bash line without creating a shell script?

Best Answer

Save and reuse $?.

test; ret=$?; report; exit $ret

If you have multiple test commands and you want to run them all, but keep track of whether one has failed, you can use bash's ERR trap.

failures=0
trap 'failures=$((failures+1))' ERR
test1
test2
if ((failures == 0)); then
  echo "Success"
else
  echo "$failures failures"
  exit 1
fi

Related Solutions

Bash – Simultaneously check for empty output and successful exit status

First of all, while they are functionally equivalent, $(…) is widely considered to be clearer than `…` — see this, this, and this. Secondly, you don’t need to use $? to check whether a command succeeded or failed. My attention was recently drawn to Section 2.9.1, Simple Commands of The Open Group Base Specifications for Shell & Utilities (Issue 7):

A "simple command" is a sequence of optional variable assignments and redirections, in any sequence, optionally followed by words and redirections, terminated by a control operator.

When a given simple command is required to be executed …
⋮ (blah, blah, blah …)

If there is a command name, execution shall continue as described in Command Search and Execution. If there is no command name, but the command contained a command substitution, the command shall complete with the exit status of the last command substitution performed. …

For example,

the exit status of the command
```
ls -ld "module_$(uname).c"
```
is the exit status from the ls, but
the exit status of the command
```
myfile="module_$(uname).c"
```
is the exit status from the uname.

So ferada’s answer can be streamlined a bit:

if output=$(/etc/grub.d/30_os-prober)  &&  [ -z "$output" ]
    # i.e., if 30_os-prober successfully produced no output
then
    install_linux_only
else
    install_dual_boot
fi

Note that it is good practice to use all-upper-case names only for environment variables (or variables to be visible throughout the script). Variables of limited scope are usually named in lower case (or, if you prefer, camelCase).

Bash – Is the exit status of a command implemented by the command or a shell process which executes the command

The command itself can provide the exit status, via the argument to an exit() system call. The shell (or other program, how about system() in Perl or PHP?) can pick up a child process' exit status via wait() or waitpid() system calls. The Unix/Linux/*BSD kernels all arrange to deliver SIGCHLD to the parent process when a child process changes status.

But there are other circumstances. A process terminated via SIGKILL doesn't have a chance to exit. A process that dereferences an invalid address won't have a chance to call exit() unless it has a SIGSEGV signal handler installed. In those cases, the kernel calculates an exit status that includes a bit that means "killed by a signal", and what signal caused the process to get killed. That kernel-calculated exit status is delivered to the killed process' parent process.

Best Answer

Related Solutions

Bash – Simultaneously check for empty output and successful exit status

Bash – Is the exit status of a command implemented by the command or a shell process which executes the command

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