Change shell and execute commands within a shell script - linux

I am facing a situation where I from within my script I have to execute a read-only-script which changes the shell and sets some environment variables. Now I need to access these environment variables from my script.
The situation is like script-A
#!/bin/csh -f
bash
#set some environment variables A,B,C
I do not have write access to script-A and it performs a lot of configurations which are necessary for my Script-B.
I have tried script-B with
#!/bin/csh -f
./script-A
echo $A
However since the shell has changed, I am unable to access $A. Is there some work around such that I can do this.
Ideally the commands in my script-B has to be run in the new environment of script-A. While interacting manually, this is fine as I can first execute script-A and then execute the required commands. However, I have to automate the whole process.

Rewrite your own script in the same shell language as the one you need to execute so that you can execute it with the shell's source command.

If script-A is a csh script, then
source script-A
This works even if script-A contains exit statements:
$ cat x.csh
#!/bin/csh
source y.csh
echo $A - $B
cat y.csh
#!/bin/csh
set A=10
set B=20
exit 1
set B=30
$ ./x.csh
10 - 20
If script-A is in another shell, you need to rewrite script-B to match that shell
Oh, and by the way, DITCH CSH if at all possible:

Related

How can I write a bash script that sets a variable that's available to the user in the terminal? [duplicate]

This question already has answers here:
Can I export a variable to the environment from a Bash script without sourcing it?
(13 answers)
Closed 3 years ago.
The community reviewed whether to reopen this question last year and left it closed:
Original close reason(s) were not resolved
I'm trying to write a shell script that, when run, will set some environment variables that will stay set in the caller's shell.
setenv FOO foo
in csh/tcsh, or
export FOO=foo
in sh/bash only set it during the script's execution.
I already know that
source myscript
will run the commands of the script rather than launching a new shell, and that can result in setting the "caller's" environment.
But here's the rub:
I want this script to be callable from either bash or csh. In other words, I want users of either shell to be able to run my script and have their shell's environment changed. So 'source' won't work for me, since a user running csh can't source a bash script, and a user running bash can't source a csh script.
Is there any reasonable solution that doesn't involve having to write and maintain TWO versions on the script?
Use the "dot space script" calling syntax. For example, here's how to do it using the full path to a script:
. /path/to/set_env_vars.sh
And here's how to do it if you're in the same directory as the script:
. set_env_vars.sh
These execute the script under the current shell instead of loading another one (which is what would happen if you did ./set_env_vars.sh). Because it runs in the same shell, the environmental variables you set will be available when it exits.
This is the same thing as calling source set_env_vars.sh, but it's shorter to type and might work in some places where source doesn't.
Your shell process has a copy of the parent's environment and no access to the parent process's environment whatsoever. When your shell process terminates any changes you've made to its environment are lost. Sourcing a script file is the most commonly used method for configuring a shell environment, you may just want to bite the bullet and maintain one for each of the two flavors of shell.
You're not going to be able to modify the caller's shell because it's in a different process context. When child processes inherit your shell's variables, they're
inheriting copies themselves.
One thing you can do is to write a script that emits the correct commands for tcsh
or sh based how it's invoked. If you're script is "setit" then do:
ln -s setit setit-sh
and
ln -s setit setit-csh
Now either directly or in an alias, you do this from sh
eval `setit-sh`
or this from csh
eval `setit-csh`
setit uses $0 to determine its output style.
This is reminescent of how people use to get the TERM environment variable set.
The advantage here is that setit is just written in whichever shell you like as in:
#!/bin/bash
arg0=$0
arg0=${arg0##*/}
for nv in \
NAME1=VALUE1 \
NAME2=VALUE2
do
if [ x$arg0 = xsetit-sh ]; then
echo 'export '$nv' ;'
elif [ x$arg0 = xsetit-csh ]; then
echo 'setenv '${nv%%=*}' '${nv##*=}' ;'
fi
done
with the symbolic links given above, and the eval of the backquoted expression, this has the desired result.
To simplify invocation for csh, tcsh, or similar shells:
alias dosetit 'eval `setit-csh`'
or for sh, bash, and the like:
alias dosetit='eval `setit-sh`'
One nice thing about this is that you only have to maintain the list in one place.
In theory you could even stick the list in a file and put cat nvpairfilename between "in" and "do".
This is pretty much how login shell terminal settings used to be done: a script would output statments to be executed in the login shell. An alias would generally be used to make invocation simple, as in "tset vt100". As mentioned in another answer, there is also similar functionality in the INN UseNet news server.
In my .bash_profile I have :
# No Proxy
function noproxy
{
/usr/local/sbin/noproxy #turn off proxy server
unset http_proxy HTTP_PROXY https_proxy HTTPs_PROXY
}
# Proxy
function setproxy
{
sh /usr/local/sbin/proxyon #turn on proxy server
http_proxy=http://127.0.0.1:8118/
HTTP_PROXY=$http_proxy
https_proxy=$http_proxy
HTTPS_PROXY=$https_proxy
export http_proxy https_proxy HTTP_PROXY HTTPS_PROXY
}
So when I want to disable the proxy,
the function(s) run in the login shell and sets the variables
as expected and wanted.
It's "kind of" possible through using gdb and setenv(3), although I have a hard time recommending actually doing this. (Additionally, i.e. the most recent ubuntu won't actually let you do this without telling the kernel to be more permissive about ptrace, and the same may go for other distros as well).
$ cat setfoo
#! /bin/bash
gdb /proc/${PPID}/exe ${PPID} <<END >/dev/null
call setenv("foo", "bar", 0)
END
$ echo $foo
$ ./setfoo
$ echo $foo
bar
This works — it isn't what I'd use, but it 'works'. Let's create a script teredo to set the environment variable TEREDO_WORMS:
#!/bin/ksh
export TEREDO_WORMS=ukelele
exec $SHELL -i
It will be interpreted by the Korn shell, exports the environment variable, and then replaces itself with a new interactive shell.
Before running this script, we have SHELL set in the environment to the C shell, and the environment variable TEREDO_WORMS is not set:
% env | grep SHELL
SHELL=/bin/csh
% env | grep TEREDO
%
When the script is run, you are in a new shell, another interactive C shell, but the environment variable is set:
% teredo
% env | grep TEREDO
TEREDO_WORMS=ukelele
%
When you exit from this shell, the original shell takes over:
% exit
% env | grep TEREDO
%
The environment variable is not set in the original shell's environment. If you use exec teredo to run the command, then the original interactive shell is replaced by the Korn shell that sets the environment, and then that in turn is replaced by a new interactive C shell:
% exec teredo
% env | grep TEREDO
TEREDO_WORMS=ukelele
%
If you type exit (or Control-D), then your shell exits, probably logging you out of that window, or taking you back to the previous level of shell from where the experiments started.
The same mechanism works for Bash or Korn shell. You may find that the prompt after the exit commands appears in funny places.
Note the discussion in the comments. This is not a solution I would recommend, but it does achieve the stated purpose of a single script to set the environment that works with all shells (that accept the -i option to make an interactive shell). You could also add "$#" after the option to relay any other arguments, which might then make the shell usable as a general 'set environment and execute command' tool. You might want to omit the -i if there are other arguments, leading to:
#!/bin/ksh
export TEREDO_WORMS=ukelele
exec $SHELL "${#-'-i'}"
The "${#-'-i'}" bit means 'if the argument list contains at least one argument, use the original argument list; otherwise, substitute -i for the non-existent arguments'.
You should use modules, see http://modules.sourceforge.net/
EDIT: The modules package has not been updated since 2012 but still works ok for the basics. All the new features, bells and whistles happen in lmod this day (which I like it more): https://www.tacc.utexas.edu/research-development/tacc-projects/lmod
Another workaround that I don't see mentioned is to write the variable value to a file.
I ran into a very similar issue where I wanted to be able to run the last set test (instead of all my tests). My first plan was to write one command for setting the env variable TESTCASE, and then have another command that would use this to run the test. Needless to say that I had the same exact issue as you did.
But then I came up with this simple hack:
First command ( testset ):
#!/bin/bash
if [ $# -eq 1 ]
then
echo $1 > ~/.TESTCASE
echo "TESTCASE has been set to: $1"
else
echo "Come again?"
fi
Second command (testrun ):
#!/bin/bash
TESTCASE=$(cat ~/.TESTCASE)
drush test-run $TESTCASE
You can instruct the child process to print its environment variables (by calling "env"), then loop over the printed environment variables in the parent process and call "export" on those variables.
The following code is based on Capturing output of find . -print0 into a bash array
If the parent shell is the bash, you can use
while IFS= read -r -d $'\0' line; do
export "$line"
done < <(bash -s <<< 'export VARNAME=something; env -0')
echo $VARNAME
If the parent shell is the dash, then read does not provide the -d flag and the code gets more complicated
TMPDIR=$(mktemp -d)
mkfifo $TMPDIR/fifo
(bash -s << "EOF"
export VARNAME=something
while IFS= read -r -d $'\0' line; do
echo $(printf '%q' "$line")
done < <(env -0)
EOF
) > $TMPDIR/fifo &
while read -r line; do export "$(eval echo $line)"; done < $TMPDIR/fifo
rm -r $TMPDIR
echo $VARNAME
Under OS X bash you can do the following:
Create the bash script file to unset the variable
#!/bin/bash
unset http_proxy
Make the file executable
sudo chmod 744 unsetvar
Create alias
alias unsetvar='source /your/path/to/the/script/unsetvar'
It should be ready to use so long you have the folder containing your script file appended to the path.
It's not what I would call outstanding, but this also works if you need to call the script from the shell anyway. It's not a good solution, but for a single static environment variable, it works well enough.
1.) Create a script with a condition that exits either 0 (Successful) or 1 (Not successful)
if [[ $foo == "True" ]]; then
exit 0
else
exit 1
2.) Create an alias that is dependent on the exit code.
alias='myscript.sh && export MyVariable'
You call the alias, which calls the script, which evaluates the condition, which is required to exit zero via the '&&' in order to set the environment variable in the parent shell.
This is flotsam, but it can be useful in a pinch.
You can invoke another one Bash with the different bash_profile.
Also, you can create special bash_profile for using in multi-bashprofile environment.
Remember that you can use functions inside of bashprofile, and that functions will be avialable globally.
for example, "function user { export USER_NAME $1 }" can set variable in runtime, for example: user olegchir && env | grep olegchir
Another option is to use "Environment Modules" (http://modules.sourceforge.net/). This unfortunately introduces a third language into the mix. You define the environment with the language of Tcl, but there are a few handy commands for typical modifications (prepend vs. append vs set). You will also need to have environment modules installed. You can then use module load *XXX* to name the environment you want. The module command is basically a fancy alias for the eval mechanism described above by Thomas Kammeyer. The main advantage here is that you can maintain the environment in one language and rely on "Environment Modules" to translate it to sh, ksh, bash, csh, tcsh, zsh, python (?!?!!), etc.
I created a solution using pipes, eval and signal.
parent() {
if [ -z "$G_EVAL_FD" ]; then
die 1 "Rode primeiro parent_setup no processo pai"
fi
if [ $(ppid) = "$$" ]; then
"$#"
else
kill -SIGUSR1 $$
echo "$#">&$G_EVAL_FD
fi
}
parent_setup() {
G_EVAL_FD=99
tempfile=$(mktemp -u)
mkfifo "$tempfile"
eval "exec $G_EVAL_FD<>'$tempfile'"
rm -f "$tempfile"
trap "read CMD <&$G_EVAL_FD; eval \"\$CMD\"" USR1
}
parent_setup #on parent shell context
( A=1 ); echo $A # prints nothing
( parent A=1 ); echo $A # prints 1
It might work with any command.
I don't see any answer documenting how to work around this problem with cooperating processes. A common pattern with things like ssh-agent is to have the child process print an expression which the parent can eval.
bash$ eval $(shh-agent)
For example, ssh-agent has options to select Csh or Bourne-compatible output syntax.
bash$ ssh-agent
SSH2_AUTH_SOCK=/tmp/ssh-era/ssh2-10690-agent; export SSH2_AUTH_SOCK;
SSH2_AGENT_PID=10691; export SSH2_AGENT_PID;
echo Agent pid 10691;
(This causes the agent to start running, but doesn't allow you to actually use it, unless you now copy-paste this output to your shell prompt.) Compare:
bash$ ssh-agent -c
setenv SSH2_AUTH_SOCK /tmp/ssh-era/ssh2-10751-agent;
setenv SSH2_AGENT_PID 10752;
echo Agent pid 10752;
(As you can see, csh and tcsh uses setenv to set varibles.)
Your own program can do this, too.
bash$ foo=$(makefoo)
Your makefoo script would simply calculate and print the value, and let the caller do whatever they want with it -- assigning it to a variable is a common use case, but probably not something you want to hard-code into the tool which produces the value.
Technically, that is correct -- only 'eval' doesn't fork another shell. However, from the point of view of the application you're trying to run in the modified environment, the difference is nil: the child inherits the environment of its parent, so the (modified) environment is conveyed to all descending processes.
Ipso facto, the changed environment variable 'sticks' -- as long as you are running under the parent program/shell.
If it is absolutely necessary for the environment variable to remain after the parent (Perl or shell) has exited, it is necessary for the parent shell to do the heavy lifting. One method I've seen in the documentation is for the current script to spawn an executable file with the necessary 'export' language, and then trick the parent shell into executing it -- always being cognizant of the fact that you need to preface the command with 'source' if you're trying to leave a non-volatile version of the modified environment behind. A Kluge at best.
The second method is to modify the script that initiates the shell environment (.bashrc or whatever) to contain the modified parameter. This can be dangerous -- if you hose up the initialization script it may make your shell unavailable the next time it tries to launch. There are plenty of tools for modifying the current shell; by affixing the necessary tweaks to the 'launcher' you effectively push those changes forward as well.
Generally not a good idea; if you only need the environment changes for a particular application suite, you'll have to go back and return the shell launch script to its pristine state (using vi or whatever) afterwards.
In short, there are no good (and easy) methods. Presumably this was made difficult to ensure the security of the system was not irrevocably compromised.
The short answer is no, you cannot alter the environment of the parent process, but it seems like what you want is an environment with custom environment variables and the shell that the user has chosen.
So why not simply something like
#!/usr/bin/env bash
FOO=foo $SHELL
Then when you are done with the environment, just exit.
You could always use aliases
alias your_env='source ~/scripts/your_env.sh'
I did this many years ago. If I rememeber correctly, I included an alias in each of .bashrc and .cshrc, with parameters, aliasing the respective forms of setting the environment to a common form.
Then the script that you will source in any of the two shells has a command with that last form, that is suitable aliased in each shell.
If I find the concrete aliases, I will post them.
Other than writings conditionals depending on what $SHELL/$TERM is set to, no. What's wrong with using Perl? It's pretty ubiquitous (I can't think of a single UNIX variant that doesn't have it), and it'll spare you the trouble.

Difference with running a script using source and ./ [duplicate]

csh:
set a=0
echo "a is $a"
when i do ./my_script.csh output is:
a is
when i do source my_script.csh output is:
a is 0
Why is it so . As i know that ./ execution uses new shell.
That's right, ./my_script.csh starts a new shell, and uses the #! that you should have at the top of the file to select which shell to run (which should be csh in this case).
source my_script.csh runs the script in the current shell.
If the script is incorrectly run in, for example, the bash shell, set a=0 is not the syntax for setting an environment variable in bash, so the code won't work as you expected, because you're using the wrong shell.
Take a look at the #! at the top of the file. Is it correct?
check if variable "a" is set in your current shell:
set | grep '^a='
Remember that once you source script to your current shell,
all it's global variables are there until unset or you exit the current shell.
You may want to start a new shell, source the script, end exit shell to perform valid tests.
I don't know the context of your problem, but you may want to export some key variables to have their copies in every subprocess.

Change shell within a script between shell and tcsh

I have a situation where my default shell is set to sh or bash in the script. I have to change my shell in order to execute certain commands in tcsh. When I am doing this, I am not able to set the variables.
#!/bin/sh
Variables=/path/set
tcsh
vendor_command.sh
ret=$?
if (ret!= 0)
exit "$ret"
else
echo "success"
fi
Is there a way to do this?
Answering the literal question: No, you cannot seamlessly switch between scripting languages, passing shell-local variables bidirectionally between them, without implementing that data-passing protocol yourself.
You can embed a tcsh script in your POSIX sh script, as so:
#!/bin/sh
# this is run with POSIX sh
export var1="tcsh can see this"
var2="tcsh cannot see this"
tcsh <<'EOF'
# this is run with tcsh
# exported variables (not shell-local variables!) from above are present
var3="calling shell cannot see this, even if exported"
EOF
# this is run in the original POSIX sh shell after tcsh has exited
# only variables set in the POSIX shell, not variables set by tcsh, are available
...however, when the tcsh interpreter exits, all its variables disappear with it. To pass state around otherwise, you'd need to either emit content on stdout and read or evaluate it; write contents to a file; or otherwise explicitly implement some interface to pass data between the two scripts.
All that said, your example is trivially rewritten with no need for tcsh at all:
#!/bin/sh -a
# the -a above makes your variables automatically exported
# ...so that they can be seen by the vendor's script.
Variables=/path/set
# If vendor_command exits with a nonzero exit status, this
# ...makes the script exit with that same status.
vendor_command.sh || exit
echo "success"

incrementing an environmental variable

I need to increment an environmental variable by these steps:
envar=1
export envar
sh script_incrementation
echo $envar
where script_incrementation contains something like this:
#! /bin/sh
envar=$[envar+1] #I've tried also other methods of incrementation
export envar
Whatever I do, after exiting the script the variable remains with its initial value 1.
THanks for your time.
A shell script executes in its own shell, so you cannot affect the outer shell unless you source it. See this question for details of that discussion.
Consider the following script, which I will call Foo.sh.
#!/bin/bash
export HELLO=$(($HELLO+1))
Suppose in the outer shell, I define an environmental variable:
export HELLO=1
If I run the script like this, it run inside its own shell and will not affect the parent.
./Foo.sh
However, if I source it, it will just execute the commands in the current shell, and will achieve the desired affect.
. Foo.sh
echo $HELLO # prints 2
Your script can not change the environment of the calling process (shell), it merely inherits it.
So, if you export foo=bar, and then invoke sh (a new process) with your script, the script will see the value of $foo (which is "bar"), and it will be able to change its own copy of it – but that is not going to affect the environment of the parent process (where you exported the variable).
You can simply source your script in the original shell, i.e. run
source increment_script.sh
or
. increment_script.sh
and that will then change the value of the variable.
This is because sourceing a script avoids spawning a new shell (process).
Another trick is to have your script output the changed environment, and then eval that output, for example:
counter=$[counter+1]
echo "counter=$counter"
and then run that as
eval `increment_script.sh`

How to run a csh script from a sh script

I was wondering if there is a way to source a csh script from a sh script. Below is an example of what is trying to be implemented:
script1.sh:
#!/bin/sh
source script2
script2:
#!/bin/csh -f
setenv TEST 1234
set path = /home/user/sandbox
When I run sh script1.sh, I get syntax errors generated from script2 (expected since we are using a different Shebang). Is there a way I can run script2 through script1?
Instead of source script2 run it as:
csh -f script2
Since your use case depends on retaining environment variables set by the csh script, try adding this to the beginning of script1:
#!/bin/sh
if [ "$csh_executed" -ne 1 ]; then
csh_executed=1 exec csh -c "source script2;
exec /bin/sh \"$0\" \"\$argv\"" "$#"
fi
# rest of script1
If the csh_executed variable is not set to 1 in the environment, run a csh script that sources script2 then executes an instance of sh, which will retain the changes to the environment made in script2. exec is used to avoid creating new processes for each shell instance, instead just "switching" from one shell to the next. Setting csh_executed in the environment of the csh command ensures that we don't get stuck in a loop when script1 is re-executed by the csh instance.
Unfortunately, there is one drawback that I don't think can be fixed, at least not with my limited knowledge of csh: the second invocation of script1 receives all the original arguments as a single string, rather than a sequence of distinct arguments.
You don't want source there; it runs the given script inside your existing shell, without spawning a subprocess. Obviously, your sh process can't run something like that which isn't a sh script.
Just call the script directly, assuming it is executable:
script2
The closest you can come to sourcing a script with a different executor than your original script is to use exec. exec will replace the running process space with the new process. Unlike source, however, when your exec-ed program ends, the entire process ends. So you can do this:
#!/bin/sh
exec /path/to/csh/script
but you can't do this:
#!/bin/sh
exec /path/to/csh/script
some-other-command
However, are you sure you really want to source the script? Maybe you just want to run it in a subprocess:
#!/bin/sh
csh -f /path/to/csh/script
some-other-command
You want the settings in your csh script to apply to the sh script that invokes it.
Basically, you can't do that, though there are some (rather ugly) ways you could make it work. If you execute your csh script, it will set those variables in the context of the process running the script; they'll vanish as soon as it returns to the caller.
Your best bet is simply to write a new version of your csh script as an sh script, and source or . it from the calling sh script.
You could translate your csh script:
#!/bin/csh -f
setenv TEST 1234
set path = /home/user/sandbox
to this:
export TEST=1234
export PATH=/home/user/sandbox
(csh treats the shell array variable $path specially, tying it to the environment variable $PATH. sh and its derivatives don't do that, they deal with $PATH itself directly.)
Note that a script intended to be sourced should not have a #! line at the top, since it doesn't make sense to execute it in its own process; you need to execute its contents in the context of the caller.
If maintaining two copies of the script, one to be sourced from csh or tcsh scripts and another to be sourced or .ed from sh/ksh/bash/zsh script, is not practical, there are other solutions. For example, your script can print a series of sh commands to be executed; you can then do something like
eval `./foo.csh`
(line endings will pose some issues here).
Or you can modify the csh script so it sets the required environment variables and then invokes some specified command, which could be a new interactive shell; this is inconvenient, since it doesn't set those variables in the interactive shell you're running.
If a software package requires some special environment variables to be set, it's common practice to provide scripts called, for example, setup.sh and setup.csh, so that sh/ksh/bash/zsh users can do:
. /path/to/package/setup.sh
and csh/tcsh users can do:
source /path/to/package/setup.csh
Incidentally, this command:
set path = /home/user/sandbox
in your sample script is probably not a good idea. It replaces your entire $PATH with just a single directory, which means you won't be able to execute simple commands like ls unless you specify their full paths. You'd usually want something like:
set path = ( $path /home/user/sandbox )
or, in sh:
PATH=$PATH:/home/user/sandbox

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