I have a script, generate some output just as what the echo below does. How to export the two environment variables a and b?
I tried
echo -e "export a=3\nexport b=4"|bash
or
echo -e "export a=3\nexport b=4"|eval
or
echo -e "export a=3\nexport b=4"|exec
Neither works. Please help.
If you pipe the command to a program, the program runs in a child process, so none of its environment changes affect the original shell.
Use eval and give the string as an argument. Use ; to separate commands rather than newline.
eval 'export a=3; export b=4'
Related
I have a bash shell-script with a function which exports an environment variable.
For sake of argument lets use the following example:
#!/bin/bash
function my_function()
{
export my_env_var=$1
}
Since the whole purpose is to export the variable to the main shell I source it.
When the main shell is bash this works fine:
<bash-shell>
> source ~/tmp/my_test.sh
> my_function test
> echo $my_env_var
test
But other customers use csh and there things start to fail if I use the same command with the same script, since csh does not know functions :-(
<csh-shell>
% source ~/tmp/my_test.sh
Badly placed ()'s
I already tried to wrap it in a wrapper-script:
#!/bin/sh
bash -c 'source ~/tmp/my_test.sh; my_function test`
echo my_env_var = $my_env_var
But my_env_var is not exported in this way:
<csh-shell>
% source ~/tmp/my_test2.sh
my_env_var: Undefined variable.
Where it is known in the bash shell (as can be seen by changing the 2nd script to:
#!/bin/sh
bash -c 'source ~/tmp/my_test.sh; my_function test; echo my_env_var in bash = $my_env_var`
echo my_env_var = $my_env_var
<csh-shell>
% source ~/tmp/my_test2.sh
my_env_var in bash = test
my_env_var: Undefined variable.
What am I missing / doing wrong so the script exports the variable when it is called from bash and when it is called from csh?
The Bourne shell and csh are not compatible; many commands are different, and csh misses many features (it doesn't have functions at all). Plus, sooner or later you're going to have someone who uses fish, which is different yet still. The only way to make a non-trivial script work for both is to write it twice.
That said, if you want to set some environment variables then the general strategy is to create a script which outputs the required commands; this can be in any language (shell, Python, C); for example:
#!/bin/sh
# ... do work here ...
var="foo"
# Getting the shell in a cross-platform way isn't too easy. This was only tested
# on Linux. Can add a "-c" or "-f" flag if you need cross-platform support.
shell=$(ps -ho comm $(ps -ho ppid $$))
case "$shell" in
(csh|tcsh) echo "setenv VAR $var" ;;
(fish) echo "set -Ux VAR $var" ;;
(*) echo "export VAR=$var"
esac
And when you run it, it outputs the appropriate commands:
% ./work
export VAR=foo
% tcsh
> ./work
setenv VAR foo
> fish
martin#x270 ~> ./work
set -Ux VAR foo
And to actually set it, eval the output like so:
% eval $(./work)
% echo $VAR
foo
% tcsh
> eval `./work`
> echo $VAR
foo
> fish
martin#x270 ~> eval (./work)
martin#x270 ~> echo $VAR
foo
The downside of this is that informational messages, warnings, etc. will also get eval'd; to solve this make sure to always output these to stderr:
echo >&2 "warning: foo"
If you don't want to run eval you can also use something slightly more complicated which prints VAR=foo and then create a Bourne and csh wrapper script to parse those lines, but "output the variables you want to set, instead of directly setting them" is the general approach to take to make something work in multiple incompatible shells.
This is my script , even after using the export command not able to use variable outside of the block. Below is the code that i have tried. I also tried other option like declare -x var, but that is also not working.
Can someone please please comment on this , am i doing right ?
#!/bin/bash
{
var="123"
export var # exporting the variable so that i can access from anywhere
echo "var is "$var # able to get the value of this variable
} | tee log.txt
echo "var is "$var # not able to get the value of this variable
Because the pipe is causing the code between the braces to execute in a sub-shell you need to find a way to capture that data as opposed to storing it in a variable that is not accessible from the rest of the code. An example would be to store the output of a function in a variable, or to access it via command substitution. If you have script.sh as such:
#!/bin/bash
function get_pizza() {
echo "Pizza"
}
myvar=$(get_pizza)
printf "myvar is '%s'\n" $myvar
echo "Plain echo follows:"
echo $(get_pizza)
and then run bash script.sh you will get output as such:
[user#host]$ bash ./script.sh
myvar is 'Pizza'
Plain echo follows:
Pizza
Then if you still want to write to a file via tee, you can pipe your whole script to tee:
bash ./script.sh | tee foo.log
If you only want parts of the script to goto a file, you'll can also handle that with I/O redirection within the script: echo pizza > foo.log
I have variable difine as SCRPT_PATH="/home/dasitha" I need to add this path to .bashrc file using shell scirpt.
What I tired was something like this.
echo 'export PATH=$PATH:$SCRPT_PATH")' >> /root/.bashrc
After opening my .bashrc file it looks like this
export PATH=$PATH:$SCRPT_PATH")
What I actually need is export PATH=$PATH:/home/dasitha. How should I do this by changing the shell script?
You've got the wrong quotes (in addition to a spurious looking parenthesis and quote mark). You're looking for something more like
echo "export PATH=$PATH:$SCRPT_PATH" >> /root/.bashrc
Here's a quick example that demonstrates quoting:
krismatth#earth ~$ echo $HOME
/Users/krismatth
krismatth#earth ~$ echo '$HOME'
$HOME
krismatth#earth ~$ echo "$HOME"
/Users/krismatth
In the shell script, I want to grep a value from the log file and set as the value of one environment. In the log file, there is one line like this:
SOME_PATH=/some/specific/path
In my shell script, I grep the SOME_PATH keyword, and I got the above line and split it with =, but I'm now able to set the environment variable:
line=`grep "SOME_PATH" /path/to/the/log.log`
path=${line##*=}
export SOME_PATH="$path" #I cannot change the environment variable with this line.
And if I just have the script like below, the environment variable changes.
export SOME_PATH=/some/specific/path
Exported variables available either in processes spawned from shell (script) which exported a var or in another script with sourced script with export statement.
1st way:
$ cat exp.sh
#!/bin/bash
export MYVAR="hi there"
bash
# or bash -c "echo here: $MYVAR"
2nd way:
$ cat exp.sh
#!/bin/bash
export MYVAR="hi there"
$ cat imp.sh
#!/bin/bash
. exp.sh
echo $MYVAR
Here's another explanation: advanced bash scripting guide.
Let's say I have following command
$> MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR
I mean that MYENVVAR=myfolder repeats
Is it possible to set it once for both "&&" separated commands while keeping the command on one line?
Assuming you actually need it as an environment variable (even though the example code does not really need an environment variable; some shell variables are not environment variables):
(export MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)
If you don't need it as an environment variable, then:
(MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)
The parentheses create a sub-shell; environment variables (and plain variables) set in the sub-shell do not affect the parent shell. In both commands shown, the variable is set once and then used twice, once by each of the two commands.
Parentheses spawn a new process, where you can set its own variables:
( MYENVVAR=myfolder; echo 1: $MYENVVAR; ); echo 2: $MYENVVAR;
1: myfolder
2:
Wrapping the commands into a string and using eval on them is one way not yet mentioned:
a=abc eval 'echo $a; echo $a'
a=abc eval 'echo $a && echo $a'
Or, if you want to use a general-purpose many-to-many mapping between environment variables and commands, without the need to quote your commands, you can use my trap-based function below:
envMulti()
{
shopt -s extdebug;
PROMPT_COMMAND="$(trap -p DEBUG | tee >(read -n 1 || echo "trap - DEBUG")); $(shopt -p extdebug); PROMPT_COMMAND=$PROMPT_COMMAND";
eval "trap \"\
[[ \\\"\\\$BASH_COMMAND\\\" =~ ^trap ]] \
|| { eval \\\"$# \\\$BASH_COMMAND\\\"; false; }\" DEBUG";
}
Usage:
envMulti a=aaa b=bbb; eval 'echo $a'; eval 'echo $b'
Note: the eval 'echo...'s above have nothing to do with my script; you can never do a=aaa echo $a directly, because the $a gets expanded too early.
Or use it with env if you prefer (it actually prefixes any commands with anything):
echo -e '#!/bin/bash\n\necho $a' > echoScript.sh
chmod +x echoScript.sh
envMulti env a=aaa; ./echoScript.sh; ./echoScript.sh
Note: created a test script just to demonstrate usage with env, which can't accept built-ins like eval as used in the earlier demo.
Oh, and the above were all intended for running your own shell commands by-hand. If you do anything other than that, make sure you know all the cautions about using eval -- i.e. make sure you trust the source of the commands, etc.
Did you consider using export like
export MYENVVAR=myfolder
then type your commands like echo $MYENVVAR (that would work even in sub-shells) etc