I've got tcl script with two ways of execution bash script:
#exec bash ./run.sh
open "|bash ./run.sh r"
The bash script is shown below:
#!/bin/bash
ls
if [ "$?" != "0" ]; then
echo "ERROR: Status failed!" > status
else
echo "Everything is OK!" > status
fi
I'm using tclsh for Windows with bash from git bash. When I use:
exec bash ./run.sh
I've got in status file:
Everything is OK!
otherwise:
open "|bash ./run.sh r"
got:
ERROR: Status failed!
Is there any possibility to correctly detect exit code when opened the tcl pipe?
You don't describe whether you get different results out of the ls part of the script. That matters; the ls command is most certainly capable of changing its behaviour according to the environment in which it is invoked. This matters because Tcl executes subprocesses (on Windows) directly using the CreateProcess() system call, rather than the various wrapped versions that Cygwin and git bash use. Other possibilities are that you're launching the script in a different directory and so on.
However, in general we'd expect a script to behave very similarly when launched via exec or via open |… r as they share a common core of functionality. The only differences are to do with how output and termination are waited for.
If you create a subprocess pipeline, by default you won't get to find out about errors from it until you close the pipeline. exec generates any errors “immediately” because it doesn't return control to you until the subprocess has terminated and all output has been read.
Related
Let's say there's this script
#!/bin/zsh
python -c 'a'
which will fail since a isn't defined. Just before the shell script exits, I want to run a command, say echo bye. How can that be achieved?
Flow is to be:
Python command above fails.
bye appears in terminal.
The zsh script exits.
I'd prefer it to affect the python command as little as possible such as indent, putting it in an if block, checking its exit code etc. In real life, the command is in fact multiple commands.
In the script you posted, the fact that the shell exits is unrelated to any error. The shell would exit, because the last argument hast been executed. Take for instance the script
#!/bin/zsh
python -c 'a'
echo This is the End
The final echo will always be exeuted, independent of the python command. To cause the script to exit, when python returns a non-zero exit code, you would write something like
#!/bin/zsh
python -c 'a' || exit $?
echo Successful
If you want to exit a script, whenever the first one of the commands produces a non-zeror exit status, AND at the same time want to print a message, you can use the TRAPZERR callback:
#!/bin/zsh
TRAPZERR() {
echo You have an unhandled non-zero exit code in your otherwise fabulous script
exit $?
}
python -c 'a'
echo Only Exit Code 0 encountered
I have an issue that should not be too hard to solve, I just can't figure what I'm doing wrong.
I need to test if a command is successful or not, and the command needs to be executed from a script. The command is:
curl 127.0.0.1:5000 &> /dev/null
Right now there is no server running, so it should always fail. And it does fail when I execute it from a command line. However when I run it from inside a shell script, it fails but the exit code is 0. What could the cause of that be?
Here is the script:
if curl 127.0.0.1:5000 &> /dev/null
then
echo "sucess"
exit 0
else
echo "failure"
exit 1
fi
And here is the output:
success
curl: (7) Failed to connect to 127.0.0.1 port 5000: Connection refused
However, it does work as expected if I remove the redirection (I'm quite a beginner in shell code, but the redirection shouldn't also redirect the exit code right? So I really don't know what this means)
here is the code without redirections that works as expected (therefore that indicates a failure and has an exit code of 1):
if curl 127.0.0.1:5000
then
echo "sucess"
exit 0
else
echo "failure"
exit 1
fi
Anyone has an idea?
Edit:
I was launching the script with sh script_name.sh in zsh. When I use zsh script_name.sh it now works normally. I still don't fully understand why but at least it works!
"&> /dev/null" is interpreted differently in Bourne shell (sh), The "&" puts the command in background, you can test it with "sleep 100 &>/dev/null". Since it successfully put the command in background, it is a success, and the exit status of the backgrounded command is disregarded.
If you want it to work in Bourne shell (sh), use the traditional syntax ">/dev/null 2>&1", and it will work in newer shells as well, i.e. it is more compatible.
In a system where sh is linked to bash, it will work as is.
bash scripting noob here. I've found this article: https://www.shellhacks.com/print-usage-exit-if-arguments-not-provided/ that suggests putting
[ $# -eq 0 ] && { echo "Usage: $0 argument"; exit 1; }
at the top of a script to ensure arguments are passed. Seems sensible.
However, when I do that and test that that line does indeed work (by running the script without supplying any arguments: . myscript.sh) then the script does indeed exit but so does the bash session that I was calling the script from. This is very irritating.
Clearly I'm doing something wrong but I don't know what. Can anyone put me straight?
. myscript.sh is a synonym for source myscript.sh, which runs the script in the current shell (rather than as a separate process). So exit terminates your current shell. (return, on the other hand, wouldn't; it has special behaviour for sourced scripts.)
Use ./myscript.sh to run it "the normal way" instead. If that gives you a permission error, make it executable first, using chmod a+x myscript.sh. To inform the kernel that your script should be run with bash (rather than /bin/sh), add the following as the very first line in the script:
#!/usr/bin/env bash
You can also use bash myscript.sh if you can't make it executable, but this is slightly more error-prone (somebody might do sh myscript.sh instead).
Question seems not clear if you're sourcing script source script_name or . script_name it's interpreted in current bash process, if you're running a function it's the same it's running in same process, otherwise, calling a script, caller bash forks a new bash process and waits until it terminates (so running exit doesn't exit caller process), but when running exit builtin in in current bash it exits current process.
basically I have written a shell script for a homework assignment that works fine however I am having issues with exiting. Essentially the script reads numbers from the user until it reads a negative number and then does some output. I have the script set to exit and output an error code when it receives anything but a number and that's where the issue is.
The code is as follows:
if test $number -eq $number >dev/null 2>&1
then
"do stuff"
else
echo "There was an error"
exit
The problem is that we have to turn in our programs as text files using script and whenever I try to script my program and test the error cases it exits out of script as well. Is there a better way to do this?
The script is being run with the following command in the terminal
script "insert name of program here"
Thanks
If the program you're testing is invoked as a subprocess, then any exit command will only exit the command itself. The fact that you're seeing contrary behavior means you must be invoking it differently.
When invoking your script from the parent testing program, use:
# this runs "yourscript" as its own, external process.
./yourscript
...to invoke it as a subprocess, not
# this is POSIX-compliant syntax to run the commands in "yourscript" in the current shell.
. yourscript
...or...
# this is bash-extended syntax to run the commands in "yourscript" in the current shell.
source yourscript
...as either of the latter will run all the commands -- including exit -- inside your current shell, modifying its state or, in the case of exit, exec or similar, telling it to cease execution.
I want to run a executable from my shell script. The executable is located at /usr/bin/to_run.
My shell script(which is calling the above executable) is in the /usr/bin folder.
The shell script is :
#!/bin/bash
#kill all existing instances of synergy
killall synergys
sh "/usr/bin/synergys"
if [ $? -eq 1 ]; then
echo "synergy server started"
else
echo "error in starting"
fi
I am getting an error saying : "synergys : no process found".
When I run the same thing - /usr/bin/synergys directly from the terminal it runs fine, but from within a script there are problems. I don't understand why.
Thank you in advance.
That error is from the killall command, it's saying there are no candidate processes matching your argument.
If you don't want to be notified where no processes match, just use the quiet option:
killall -q synergys
From the killall man page:
-q, --quiet
Do not complain if no processes were killed.
If /usr/bin/synergys is an executable and not a shell script, you will run it directly, not via the shell:
/usr/bin/synergys
Or, since /usr/bin is on the $PATH of most people, you could simply write:
synergys
If /usr/bin/synergys is actually a shell script, it should be executable (for example, 555 or -r-xr-xr-x permissions), and you can still write just synergys to execute it. You only need to use an explicit sh if the file /usr/bin/synergys is not executable and is a shell script.