Home Can a shell script set environment variables of the calling shell?

# Can a shell script set environment variables of the calling shell?

Larry Gritz
1#
Larry Gritz Published in 2009-01-30 18:50:22Z
 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?
converter42
2#
 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.
Thomas Kammeyer
3#
Thomas Kammeyer Reply to 2015-05-20 14:51:54Z
 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.
phresus
4#
 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.
Jonathan Leffler
5#
Jonathan Leffler Reply to 2012-06-07 16:18:34Z
 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'. Davide 6# Davide Reply to 2015-10-06 14:29:48Z  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 Oleg Chirukhin 7# Oleg Chirukhin Reply to 2010-10-29 06:15:02Z  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
David Lovering
8#
David Lovering Reply to 2011-05-18 13:23:39Z
 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.
Kjetil Joergensen
9#
Kjetil Joergensen Reply to 2011-07-08 22:03:34Z
 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 ${PPID} </dev/null call setenv("foo", "bar", 0) END$ echo $foo$ ./setfoo $echo$foo bar 
GKFX
10#
 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=$https_proxy export http_proxy https_proxy HTTP_PROXY HTTPS_PROXY }  So when I want to disable the proxy, the function(s) run in the login shell and sets the variables as expected and wanted. Andrew 11# Andrew Reply to 2013-02-28 06:41:39Z  The short answer is no, you cannot alter the environment of the parent process, but it seems like what you want is an environment with custom environment variables and the shell that the user has chosen. So why not simply something like #!/usr/bin/env bash FOO=foo$SHELL  Then when you are done with the environment, just exit.
dkinzer
12#
 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 $TESTCASE  Garrett Hyde 13# Garrett Hyde Reply to 2014-04-10 23:39:37Z  You could always use aliases alias your_env='source ~/scripts/your_env.sh'  cristobal 14# cristobal Reply to 2014-06-16 12:43:43Z  Add the -l flag in top of your bash script i.e. #!/usr/bin/env bash -l ... export NAME1="VALUE1" export NAME2="VALUE2"  The values with NAME1 and NAME2 will now have been exported to your current environment, however these changes are not permanent. If you want them to be permanent you need to add them to your .bashrc file or other init file. From the man pages: -l Make bash act as if it had been invoked as a login shell (see INVOCATION below).  Community 15# Community Reply to 2017-05-23 12:34:53Z  You can instruct the child process to print its environment variables (by calling "env"), then loop over the printed environment variables in the parent process and call "export" on those variables. The following code is based on Capturing output of find . -print0 into a bash array If the parent shell is the bash, you can use while IFS= read -r -d$'\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  Howard Hobbes 16# Howard Hobbes Reply to 2014-10-23 20:02:45Z  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. Alan W. Smith 17# Alan W. Smith Reply to 2017-10-17 12:41:29Z  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. sancho.s 18# sancho.s Reply to 2015-10-30 15:14:45Z  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. Luiz Angelo Daros de Luca 19# Luiz Angelo Daros de Luca Reply to 2016-09-21 21:43:53Z  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.
 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.
 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.