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I am need of shell script which have multiple commands like
Command -1 mv
command 2- cp
command -3 - sed
command -4 echo ,append etc
rc=$?
if =0 success
else
exist30
but even though move command failed script retuning return code as 0 and script showing success message.
Do i need to main RC for all the command or can i better handle return code for each command to make sure every command run successfully
If you have to deal with commands which may fail you can do the following:
if mv ...; then
echo mv success
else
echo mv failure
rc=1
fi
exit 1
For having your script to crash with the first failed command make sure to add the line set -e below your shebang (#!/bin/sh).
Keep in mind that the error handling above is compatible with set -e, the script will not stop.
set -eu is considered best practice for shell scripts, -u will result in a crash of your script if a variable used is unset.
I'm studying the content of this preinst file that the script executes before that package is unpacked from its Debian archive (.deb) file.
The script has the following code:
#!/bin/bash
set -e
# Automatically added by dh_installinit
if [ "$1" = install ]; then
if [ -d /usr/share/MyApplicationName ]; then
echo "MyApplicationName is just installed"
return 1
fi
rm -Rf $HOME/.config/nautilus-actions/nautilus-actions.conf
rm -Rf $HOME/.local/share/file-manager/actions/*
fi
# End automatically added section
My first query is about the line:
set -e
I think that the rest of the script is pretty simple: It checks whether the Debian/Ubuntu package manager is executing an install operation. If it is, it checks whether my application has just been installed on the system. If it has, the script prints the message "MyApplicationName is just installed" and ends (return 1 mean that ends with an “error”, doesn’t it?).
If the user is asking the Debian/Ubuntu package system to install my package, the script also deletes two directories.
Is this right or am I missing something?
From help set :
-e Exit immediately if a command exits with a non-zero status.
But it's considered bad practice by some (bash FAQ and irc freenode #bash FAQ authors). It's recommended to use:
trap 'do_something' ERR
to run do_something function when errors occur.
See http://mywiki.wooledge.org/BashFAQ/105
set -e stops the execution of a script if a command or pipeline has an error - which is the opposite of the default shell behaviour, which is to ignore errors in scripts. Type help set in a terminal to see the documentation for this built-in command.
I found this post while trying to figure out what the exit status was for a script that was aborted due to a set -e. The answer didn't appear obvious to me; hence this answer. Basically, set -e aborts the execution of a command (e.g. a shell script) and returns the exit status code of the command that failed (i.e. the inner script, not the outer script).
For example, suppose I have the shell script outer-test.sh:
#!/bin/sh
set -e
./inner-test.sh
exit 62;
The code for inner-test.sh is:
#!/bin/sh
exit 26;
When I run outer-script.sh from the command line, my outer script terminates with the exit code of the inner script:
$ ./outer-test.sh
$ echo $?
26
As per bash - The Set Builtin manual, if -e/errexit is set, the shell exits immediately if a pipeline consisting of a single simple command, a list or a compound command returns a non-zero status.
By default, the exit status of a pipeline is the exit status of the last command in the pipeline, unless the pipefail option is enabled (it's disabled by default).
If so, the pipeline's return status of the last (rightmost) command to exit with a non-zero status, or zero if all commands exit successfully.
If you'd like to execute something on exit, try defining trap, for example:
trap onexit EXIT
where onexit is your function to do something on exit, like below which is printing the simple stack trace:
onexit(){ while caller $((n++)); do :; done; }
There is similar option -E/errtrace which would trap on ERR instead, e.g.:
trap onerr ERR
Examples
Zero status example:
$ true; echo $?
0
Non-zero status example:
$ false; echo $?
1
Negating status examples:
$ ! false; echo $?
0
$ false || true; echo $?
0
Test with pipefail being disabled:
$ bash -c 'set +o pipefail -e; true | true | true; echo success'; echo $?
success
0
$ bash -c 'set +o pipefail -e; false | false | true; echo success'; echo $?
success
0
$ bash -c 'set +o pipefail -e; true | true | false; echo success'; echo $?
1
Test with pipefail being enabled:
$ bash -c 'set -o pipefail -e; true | false | true; echo success'; echo $?
1
This is an old question, but none of the answers here discuss the use of set -e aka set -o errexit in Debian package handling scripts. The use of this option is mandatory in these scripts, per Debian policy; the intent is apparently to avoid any possibility of an unhandled error condition.
What this means in practice is that you have to understand under what conditions the commands you run could return an error, and handle each of those errors explicitly.
Common gotchas are e.g. diff (returns an error when there is a difference) and grep (returns an error when there is no match). You can avoid the errors with explicit handling:
diff this that ||
echo "$0: there was a difference" >&2
grep cat food ||
echo "$0: no cat in the food" >&2
(Notice also how we take care to include the current script's name in the message, and writing diagnostic messages to standard error instead of standard output.)
If no explicit handling is really necessary or useful, explicitly do nothing:
diff this that || true
grep cat food || :
(The use of the shell's : no-op command is slightly obscure, but fairly commonly seen.)
Just to reiterate,
something || other
is shorthand for
if something; then
: nothing
else
other
fi
i.e. we explicitly say other should be run if and only if something fails. The longhand if (and other shell flow control statements like while, until) is also a valid way to handle an error (indeed, if it weren't, shell scripts with set -e could never contain flow control statements!)
And also, just to be explicit, in the absence of a handler like this, set -e would cause the entire script to immediately fail with an error if diff found a difference, or if grep didn't find a match.
On the other hand, some commands don't produce an error exit status when you'd want them to. Commonly problematic commands are find (exit status does not reflect whether files were actually found) and sed (exit status won't reveal whether the script received any input or actually performed any commands successfully). A simple guard in some scenarios is to pipe to a command which does scream if there is no output:
find things | grep .
sed -e 's/o/me/' stuff | grep ^
It should be noted that the exit status of a pipeline is the exit status of the last command in that pipeline. So the above commands actually completely mask the status of find and sed, and only tell you whether grep finally succeeded.
(Bash, of course, has set -o pipefail; but Debian package scripts cannot use Bash features. The policy firmly dictates the use of POSIX sh for these scripts, though this was not always the case.)
In many situations, this is something to separately watch out for when coding defensively. Sometimes you have to e.g. go through a temporary file so you can see whether the command which produced that output finished successfully, even when idiom and convenience would otherwise direct you to use a shell pipeline.
I believe the intention is for the script in question to fail fast.
To test this yourself, simply type set -e at a bash prompt. Now, try running ls. You'll get a directory listing. Now, type lsd. That command is not recognized and will return an error code, and so your bash prompt will close (due to set -e).
Now, to understand this in the context of a 'script', use this simple script:
#!/bin/bash
# set -e
lsd
ls
If you run it as is, you'll get the directory listing from the ls on the last line. If you uncomment the set -e and run again, you won't see the directory listing as bash stops processing once it encounters the error from lsd.
set -e The set -e option instructs bash to immediately exit if any command [1] has a non-zero exit status. You wouldn't want to set this for your command-line shell, but in a script it's massively helpful. In all widely used general-purpose programming languages, an unhandled runtime error - whether that's a thrown exception in Java, or a segmentation fault in C, or a syntax error in Python - immediately halts execution of the program; subsequent lines are not executed.
By default, bash does not do this. This default behavior is exactly what you want if you are using bash on the command line
you don't want a typo to log you out! But in a script, you really want the opposite.
If one line in a script fails, but the last line succeeds, the whole script has a successful exit code. That makes it very easy to miss the error.
Again, what you want when using bash as your command-line shell and using it in scripts are at odds here. Being intolerant of errors is a lot better in scripts, and that's what set -e gives you.
copied from : https://gist.github.com/mohanpedala/1e2ff5661761d3abd0385e8223e16425
this may help you .
Script 1: without setting -e
#!/bin/bash
decho "hi"
echo "hello"
This will throw error in decho and program continuous to next line
Script 2: With setting -e
#!/bin/bash
set -e
decho "hi"
echo "hello"
# Up to decho "hi" shell will process and program exit, it will not proceed further
It stops execution of a script if a command fails.
A notable exception is an if statement. eg:
set -e
false
echo never executed
set -e
if false; then
echo never executed
fi
echo executed
false
echo never executed
cat a.sh
#! /bin/bash
#going forward report subshell or command exit value if errors
#set -e
(cat b.txt)
echo "hi"
./a.sh; echo $?
cat: b.txt: No such file or directory
hi
0
with set -e commented out we see that echo "hi" exit status being reported and hi is printed.
cat a.sh
#! /bin/bash
#going forward report subshell or command exit value if errors
set -e
(cat b.txt)
echo "hi"
./a.sh; echo $?
cat: b.txt: No such file or directory
1
Now we see b.txt error being reported instead and no hi printed.
So default behaviour of shell script is to ignore command errors and continue processing and report exit status of last command. If you want to exit on error and report its status we can use -e option.
I have a grep command that works in a bash script:
if grep 'stackoverflow' outFile.txt; then
exit 1
fi
This works fine when run on my host. When I call this from a Jenkins build step however, it exits 0 everytime, not seeing 'stackoverflow'. What is going wrong?
Add the following line as the first line in your "Execute Shell" command
#!/bin/sh
grep command exits with a non zero code when it does not find match and that causes jenkins to mark the job as failed. See Below.
In the help section of "Execute Shell"
Runs a shell script (defaults to sh, but this is configurable) for building the project. The script will be run with the workspace as the current directory. Type in the contents of your shell script. If your shell script has no header line like #!/bin/sh —, then the shell configured system-wide will be used, but you can also use the header line to write script in another language (like #!/bin/perl) or control the options that shell uses.
By default, the shell will be invoked with the "-ex" option. So all of the commands are printed before being executed, and the build is considered a failure if any of the commands exits with a non-zero exit code. Again, add the #!/bin/... line to change this behavior.
As a best practice, try not to put a long shell script in here. Instead, consider adding the shell script in SCM and simply call that shell script from Jenkins (via bash -ex myscript.sh or something like that), so that you can track changes in your shell script.
I am a bit confused by the answers on this question! i.e. Sorry, but the answers here are incorrect for this question. The question is good/interesting as plain grep in scripts does cause scripts to exit with failure if the grep is not successful (which can be unexpected), whereas a grep inside an if will not cause exit with failure.
For the example shown in the question exit 1 will be done IF the grep command runs successfully(file exists) AND if the string is found in file. (grep command returns 0 exit code to if).
#Gonen's comment to add 'ls -l outFile.txt' should have been followed up on to see what the real reason for failure was.
TLDR; if catches the exit code of commands inside the if clause:
A grep command that 'fails'(no match or error) inside an if statement in jenkins will not cause jenkins script to stop. Whereas a grep command that fails not inside an if will cause jenkins to stop and exit with fail.
The exit/return code handling is different for commands inside an if statement in shell. if catches the return code and no matter if command was successful or failed the if will return success to $0(after if) (and do actions in if or else).
From man bash:
if list; then list; [ elif list; then list; ] ... [ else list; ] fi
The if list is executed. If its exit status is zero, the then list is executed. Otherwise, each elif list is executed in turn, and
if its exit status is zero, the corresponding then list is executed
and the command completes. Otherwise, the else list is executed, if
present. The exit status is the exit status of the last command
executed, or zero if no condition tested true.
To illustrate, try this (same result in bash or sh):
$ if grep foo bar ; then echo got it; fi; echo $?
grep: bar: No such file or directory
0
$ touch bar
$ if grep foo bar ; then echo got it; fi; echo $?
0
$ echo foo >bar
$ if grep foo bar ; then echo got it; fi; echo $?
foo
got it
0
$ if grep foo bar ; then echo gotit; grep gah mah; fi; echo $?
foo
gotit
grep: mah: No such file or directory
2
I think you have error in your script. You must add 'fi' at the end of 'if' block:
if grep 'stackoverflow' outFile.txt; then
exit 1
fi
If the two were exactly the same it should work. Is your current directory or user different in the two environments? You might not be able to read the file.
I have a bash script that is supposed to check for a running instance of a program and if its not running execute a command (echo for testing purposes). The problem is, that bash isn't executing the command even though it works when I copy/paste the command directly to the command line. I imagine my issue is simple and caused by my naivety with the script language.
The line in question:
ps -ef | grep -v grep | grep $SCRIPT > /dev/null || echo "`date` - $0 : $SCRIPT stopped. Restarting..."
If I paste it to the command line it works perfect, but when I run my script nothing happens. Suggestions?
EDIT: I believe I've resolved the issue. The script that is run to check the queue_reader.sh script I foolishly named check_queue_reader.sh" so the ps -ef command was finding itself preventing the || from executing.
See edit on original post.
The script I was running was called "check_queue_reader.sh" and was using grep to search ps -ef for "queue_reader.sh". This caused the script to locate itself thus failing the check when it got to ||
Is it possible for a shell script to test whether it was executed through source? That is, for example,
$ source myscript.sh
$ ./myscript.sh
Can myscript.sh distinguish from these different shell environments?
I think, what Sam wants to do may be not possible.
To what degree a half-baken workaround is possible, depends on...
...the default shell of users, and
...which alternative shells they are allowed to use.
If I understand Sam's requirement correctly, he wants to have a 'script',
myscript, that is...
...not directly executable via invoking it by its name myscript
(i.e. that has chmod a-x);
...not indirectly executable for users by invoking sh myscript or
invoking bash myscript
...only running its contained functions and commands if invoked by
sourcing it: . myscript
The first things to consider are these
Invoking a script directly by its name (myscript) requires a first line in
the script like #!/bin/bash or similar. This will directly determine which
installed instance of the bash executable (or symlink) will be invoked to run
the script's content. This will be a new shell process. It requires the
scriptfile itself to have the executable flag set.
Running a script by invoking a shell binary with the script's (path+)name as
an argument (sh myscript), is the same as '1.' -- except that the
executable flag does not need to be set, and said first line with the
hashbang isn't required either. The only thing needed is that the invoking
user needs read access to the scriptfile.
Invoking a script by sourcing its filename (. myscript) is very much the
same as '1.' -- exept that it isn't a new shell that is invoked. All the
script's commands are executed in the current shell, using its environment
(and also "polluting" its environment with any (new) variables it may set or
change. (Usually this is a very dangerous thing to do: but here it could be
used to execute exit $RETURNVALUE under certain conditions....)
For '1.':
Easy to achieve: chmod a-x myscript will prevent myscript from being
directly executable. But this will not fullfill requirements '2.' and '3.'.
For '2.' and '3.':
Much harder to achieve. Invokations by sh myscript require reading
privileges for the file. So an obvious way out would seem to chmod a-r
myscript. However, this will also dis-allow '3.': you will not be able to
source the script either.
So what about writting the script in a way that uses a Bashism? A Bashism is a
specific way to do something which other shells do not understand: using
specific variables, commands etc. This could be used inside the script to
discover this condition and "do something" about it (like "display warning.txt",
"mailto admin" etc.). But there is no way in hell that this will prevent sh or
bash or any other shell from reading and trying to execute all the following
commands/lines written into the script unless you kill the shell by invoking
exit.
Examples: in Bash, the environment seen by the script knows of $BASH,
$BASH_ARGV, $BASH_COMMAND, $BASH_SUBSHELL, BASH_EXECUTION_STRING... . If
invoked by sh (also if sourced inside a sh), the executing shell will see
all these $BASH_* as empty environment variables. Again, this could be used
inside the script to discover this condition and "do something"... but not
prevent the following commands from being invoked!
I'm now assuming that...
...the script is using #!/bin/bash as its first line,
...users have set Bash as their shell and are invoking commands in the
following table from Bash and it is their login shell,
...sh is available and it is a symlink to bash or dash.
This will mean the following invokations are possible, with the listed values
for environment variables
vars+invok's | ./scriptname | sh scriptname | bash scriptname | . scriptname
---------------+--------------+---------------+-----------------+-------------
$0 | ./scriptname | ./scriptname | ./scriptname | -bash
$SHLVL | 2 | 1 | 2 | 1
$SHELLOPTS | braceexpand: | (empty) | braceexpand:.. | braceexpand:
$BASH | /bin/bash | (empty) | /bin/bash | /bin/bash
$BASH_ARGV | (empty) | (empty) | (empty) | scriptname
$BASH_SUBSHELL | 0 | (empty) | 0 | 0
$SHELL | /bin/bash | /bin/bash | /bin/bash | /bin/bash
$OPTARG | (empty) | (empty) | (emtpy) | (emtpy)
Now you could put a logic into your text script:
If $0 is not equal to -bash, then do an exit $SOMERETURNVALUE.
In case the script was called via sh myscript or bash myscript, then it will
exit the calling shell. In case it was run in the current shell, it will
continue to run. (Warning: in case the script has any other exit statements,
your current shell will be 'killed'...)
So put into your non-executable myscript.txt near its beginning something like
this may do something close to your goal:
echo BASH=$BASH
test x${BASH} = x/bin/bash && echo "$? : FINE.... You're using 'bash ...'"
test x${BASH} = x/bin/bash || echo "$? : RATS !!! -- You're not using BASH and I will kick you out!"
test x${BASH} = x/bin/bash || exit 42
test x"${0}" = x"-bash" && echo "$? : FINE.... You've sourced me, and I'm your login shell."
test x"${0}" = x"-bash" || echo "$? : RATS !!! -- You've not sourced me (or I'm not your bash login shell) and I will kick you out!"
test x"${0}" = x"-bash" || exit 33
This may or may not be what the asker wanted but, on a similar situation, I wanted a script to indicate that it is meant to be sourced and not directly run.
To achieve this effect my script reads:
#!/bin/echo Should be run as: source
export SOMEPATH="/some/path/on/my/system"
echo "Your environment has been set up"
So when I run it either as a command or sourced I get:
$ ./myscript.sh
Should be run as: source ./myscript.sh
$ source ./myscript.sh
Your environment has been set up
You can of course fool the script by running it as sh ./myscript.sh, but at least it gives the correct expected behaviour on 2 out of 3 cases.
This is what I was looking for:
[[ ${BASH_SOURCE[0]} = $0 ]] && main "$#"
I cannot add comment yet (stackexchange policies) so I add my own answer:
This one may works regardless if we do:
bash scriptname
scriptname
./scriptname.
on both bash and mksh.
if [ "${0##/*}" == scriptname ] # if the current name is our script
then
echo run
else
echo sourced
fi
If you have a non-altering file path for regular users, then:
if [ "$(/bin/readlink -f "$0")" = "$KNOWN_PATH_OF_THIS_FILE" ]; then
# the file was executed
else
# the file was sourced
fi
(it can also easily be loosened to only check for the filename or whatever).
But your users need to have read permission to be able to source the file, so absolutely nothing can stop them from doing what they want with the file. But it might help them out to not use it in the wrong way.
This solution is not dependent on Bashisms.
Yes it is possible. In general you can do the following:
#! /bin/bash
sourced () {
echo Sourced
}
executed () {
echo Executed
}
if [[ ${0##*/} == -* ]]; then
sourced
else
executed $#
fi
Giving the following output:
$ ./myscript
Executed
$ . ./myscript
Sourced
Based on Kurt Pfeifle’s answer, this works for me
if [ $SHLVL = 1 ]
then
echo 'script was sourced'
fi
Example
Since all of our machines have history, I did this:
check_script_call=$(history |tail -1|grep myscript.sh )
if [ -z "$check_script_call" ];then
echo "This file should be called as a source."
echo "Please, try again this way:"
echo "$ source /path/to/myscript.sh"
exit 1
fi
Everytime you run a script (without source), your shell creates a new env without history.
If you want to care about performance you can try this:
if ! history |tail -1|grep set_vars ;then
echo -e "This file should be called as a source.\n"
echo "Please, try again this way:"
echo -e "$ source /path/to/set_vars\n"
exit 1
fi
PS: I think Kurt's answer is much more complete but I think this could help.
In the first case, $0 will be "myscript.sh". In the second case, it will be "./myscript". But, in general, there's no way to tell source was used.
If you tell us what you're trying to do, instead of how you want to do it, a better answer might be forthcoming.