CODEWITHSUNDEEP
shellubuntu
CppLearner
CppLearner

Reputation: 17040

How do you export a variable through shell script?

a.sh

#! /bin/sh
export x=/usr/local

we can do source ./a in command-line. But I need to do the export through shell script.

b.sh

#! /bin/sh
. ~/a.sh

no error... but $x in command-line will show nothing. So it didn't get export.

Any idea how to make it work?

a.sh

#! /bin/sh
export x=/usr/local
-----------
admin@client: ./a.sh
admin@client: echo $x

admin@client:  <insert ....>

Upvotes: 27

Views: 94999

Answers (6)

Emmanuel
Emmanuel

Reputation: 17051

You can put export statements in a shell script and then use the 'source' command to execute it in the current process:

source a.sh

Upvotes: 122

Alexandru Ast
Alexandru Ast

Reputation: 31

script1.sh

shell_ppid=$PPID
shell_epoch=$(grep se.exec_start "/proc/${shell_ppid}/sched" | sed 's/[[:space:]]//g' | cut -f2 -d: | cut -f1 -d.)
now_epoch=$(($(date +%s%N)/1000000))
shell_start=$(( (now_epoch - shell_epoch)/1000 ))
env_md5=$(md5sum <<<"${shell_ppid}-${shell_start}"| sed 's/[[:space:]]//g' | cut -f1 -d-)
tmp_dir="/tmp/ToD-env-${env_md5}"
mkdir -p "${tmp_dir}"
ENV_PROPS="${tmp_dir}/.env"
echo "FOO=BAR" > "${ENV_PROPS}"

script2.sh

shell_ppid=$PPID
shell_epoch=$(grep se.exec_start "/proc/${shell_ppid}/sched" | sed 's/[[:space:]]//g' | cut -f2 -d: | cut -f1 -d.)
now_epoch=$(($(date +%s%N)/1000000))
shell_start=$(( (now_epoch - shell_epoch)/1000 ))
env_md5=$(md5sum <<<"${shell_ppid}-${shell_start}"| sed 's/[[:space:]]//g' | cut -f1 -d-)
tmp_dir="/tmp/ToD-env-${env_md5}"
mkdir -p "${tmp_dir}"
ENV_PROPS="${tmp_dir}/.env"
source "${ENV_PROPS}"
echo $FOO

./script1.sh
./script2.sh
BAR

It persists for the scripts run in the same parent shell, and it prevents collisions.

Upvotes: 0

WillC
WillC

Reputation: 977

Answering my own question here, using the answers above: if I have more than one related variable to export which use the same value as part of each export, I can do this:

#!/bin/bash
export TEST_EXPORT=$1
export TEST_EXPORT_2=$1_2
export TEST_EXPORT_TWICE=$1_$1

and save as e.g. ~/Desktop/TEST_EXPORTING

and finally $chmod +x ~/Desktop/TEST_EXPORTING

--

After that, running it with source ~/Desktop/TEST_EXPORTING bob

and then checking with export | grep bob should show what you expect.

Upvotes: 6

Chris Stratton
Chris Stratton

Reputation: 40357

You can't do an export through a shell script, because a shell script runs in a child shell process, and only children of the child shell would inherit the export.

The reason for using source is to have the current shell execute the commands

It's very common to place export commands in a file such as .bashrc which a bash will source on startup (or similar files for other shells)

Another idea is that you could create a shell script which generates an export command as it's output:

shell$ cat > script.sh
#!/bin/sh
echo export foo=bar
^D
chmod u+x script.sh

And then have the current shell execute that output

shell$ `./script.sh`

shell$ echo $foo
bar

shell$ /bin/sh
$ echo $foo
bar

(note above that the invocation of the script is surrounded by backticks, to cause the shell to execute the output of the script)

Upvotes: 31

Casey Comendant
Casey Comendant

Reputation: 11

Another way you can do it (to steal/expound upon the idea above), is to put the script in ~/bin and make sure ~/bin is in your PATH. Then you can access your variable globally. This is just an example I use to compile my Go source code which needs the GOPATH variable to point to the current directory (assuming you're in the directory you need to compile your source code from):

From ~/bin/GOPATH:

#!/bin/bash

echo declare -x GOPATH=$(pwd)

Then you just do:

#> $(GOPATH)

So you can now use $(GOPATH) from within your other scripts too, such as custom build scripts which can automatically invoke this variable and declare it on the fly thanks to $(pwd).

Upvotes: 1

Mark Reed
Mark Reed

Reputation: 95252

Exporting a variable into the environment only makes that variable visible to child processes. There is no way for a child to modify the environment of its parent.

Upvotes: 3

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