Bash Scripting; alias command inside a x.sh script - bash

I'm trying to write a simple script using bash which must take two variables: a name and a command; then apply these two variables inside a "alias" command like so: alias $1=$2.
It`s for an online school activity which teaches introduction to bash scripting.
What I have come up with is:
function doalias {
alias $1=$2
}
doalias $1 $2
Next thing I do is write inside the terminal ./doalias.sh inst "sudo apt-get install".
Now the message I get from the bash terminal is that "=" is not recognized as a command. Why is this and how can I solve it?

You need to put the passed parameter in quotes when actioning the alias command and so:
function doalias {
alias "$1=$2"
}
doalias "$1" "$2"
To have the alias set in the current shell, you will need to source the script and so:
source doalias.sh inst "sudo apt-get install"

Related

Is there a way to execute a bash script in Cygwin without explicitly typing bash my_script_name.sh?

I have a bash script that contains an AWK program:
#!/bin/bash
awk -v ARPT_IDENT=$1 '
BEGIN { FS=OFS="\t" }
$1 == ARPT_IDENT { print }' ANAV.TXT
I named the script file: select-NAV-for-ARPT_IDENT.sh
I can execute the script at a Cygwin command line like this:
bash select-ANAV-for-ARPT_IDENT.sh US01017
That works fine.
But, but, but, ...
I would really like to execute the script by just specifying the name of the script:
select-ANAV-for-ARPT_IDENT.sh US01017
Is there a way to execute a bash script in Cygwin without explicitly typing bash ...?
Note: I did try this: chmod +x select-ANAV-for-ARPT_IDENT.sh
And then executed it:
select-ANAV-for-ARPT_IDENT.sh US01017
But bash gave this error message:
-bash: select-ANAV-for-ARPT_IDENT.sh: command not found
Either specify the path to the script, or save it to a directory that's present in the $PATH variable.

Can I add a parameter in-between my command? [duplicate]

This question already has answers here:
Make a Bash alias that takes a parameter?
(24 answers)
Closed 3 years ago.
Coding is one of my weaker areas and this is my first question on Stack Overflow.
What I want to is add a parameter in-between my command, and I'm thinking it can be done with an alias or function.
The command I am using is telnet and it is used to log into our switches.
The full command:
$ telnet switchname.compname.com
What I want to type:
$ enter 'switchname'
In turn, making the telnet command a simple enter and not having to consistently type .compname.com every time.
A simple function does nicely:
enter() { telnet $1.compname.com; }
Create a function to open the telnet session to the switchname given by the first argument (or to your default switchname if no argument is provided), e.g. in .bashrc you could do:
mytelnet() {
local swname=${1:-defaultname} ## use local vars within function
telnet $swname.compname.com ## connect to your switch
}
Then create the alias you want for enter, e.g.
alias enter='mytelnet'
Now at the command line you can type:
$ enter ## to go to defaultname.compname.com
or
$ enter switchname ## to go to switchname.compname.com
For testing you can just enter the function and alias on the command line, e.g.
$ mytelnet() { local swname=${1:-defaultname}; telnet $swname.compname.com; }
$ alias enter='mytelnet'
Then telnet away...
(note: you can simply name your function enter() and do away with the alias. I just find it convenient to define my functions at the top of my .bashrc and then create aliases, as needed, in the various sections below, but using an alias is by no means a requirement)
Try to use an alias in your rcfile, like ~/.bashrc, for example.
alias mytelnet='telnet the.desired.site'
Then source your rcfile like
source ~/.bashrc
or the equivalent
. ~/.bashrc
and type mytelnet to execute the command.
Or just use a bash variable, like
VAR="the.desired.site"
and execute telnet this way:
telnet $VAR
Also you can add a function to your rc file, like David C. Rankin mentioned.
function mytelnet () {
telnet <<< "$#"
}
export -f mytelnet
<<< "$#" will feed telnet in the same way, as if you are using any other command on the commandline with their additional parameters, like in bash $1, $2 and so on.
export -f marks the function mytelnet to be passed to child processes in your environment.

Script not working as Command line

i've created simple bash script that do the following
:
#!/usr/bin/env bash
cf ssh "$1"
When I run the command line from the CLI like cf ssh myapp its running as expected, but when I run the script like
. myscript.sh myapp
I got error: App not found
I dont understand what is the difference, I've provided the app name after I invoke the script , what could be missing here ?
update
when I run the script with the following its working, any idea why the "$1" is not working ...
#!/usr/bin/env bash
cf ssh myapp
When you do this:
. myscript.sh myapp
You don't run the script, but you source the file named in the first argument. Sourcing means reading the file, so it's as if the lines in the file were typed on the command line. In your case what happens is this:
myscript.sh is treates as the file to source and the myapp argument is ignored.
This line is treated as a comment and skipped.
#!/usr/bin/env bash
This line:
cf ssh "$1"
is read as it stands. "$1" takes the value of $1 in the calling shell. Possibly - most likely in your case - it's blank.
Now you should know why it works as expected when you source this version of your script:
#!/usr/bin/env bash
cf ssh myapp
There's no $1 to resolve, so everything goes smoothly.
To run the script and be able to pass arguments to it, you need to make the file executable and then execute it (as opposed to sourcing). You can execute the script for example this way:
./script.bash arg1 arg2

Shell: How to call one shell script from another shell script?

I have two shell scripts, a.sh and b.sh.
How can I call b.sh from within the shell script a.sh?
There are a couple of different ways you can do this:
Make the other script executable with chmod a+x /path/to/file(Nathan Lilienthal's comment), add the #!/bin/bash line (called shebang) at the top, and the path where the file is to the $PATH environment variable. Then you can call it as a normal command;
Or call it with the source command (which is an alias for .), like this:
source /path/to/script
Or use the bash command to execute it, like:
/bin/bash /path/to/script
The first and third approaches execute the script as another process, so variables and functions in the other script will not be accessible.
The second approach executes the script in the first script's process, and pulls in variables and functions from the other script (so they are usable from the calling script).
In the second method, if you are using exit in second script, it will exit the first script as well. Which will not happen in first and third methods.
Check this out.
#!/bin/bash
echo "This script is about to run another script."
sh ./script.sh
echo "This script has just run another script."
There are a couple of ways you can do this. Terminal to execute the script:
#!/bin/bash
SCRIPT_PATH="/path/to/script.sh"
# Here you execute your script
"$SCRIPT_PATH"
# or
. "$SCRIPT_PATH"
# or
source "$SCRIPT_PATH"
# or
bash "$SCRIPT_PATH"
# or
eval '"$SCRIPT_PATH"'
# or
OUTPUT=$("$SCRIPT_PATH")
echo $OUTPUT
# or
OUTPUT=`"$SCRIPT_PATH"`
echo $OUTPUT
# or
("$SCRIPT_PATH")
# or
(exec "$SCRIPT_PATH")
All this is correct for the path with spaces!!!
The answer which I was looking for:
( exec "path/to/script" )
As mentioned, exec replaces the shell without creating a new process. However, we can put it in a subshell, which is done using the parantheses.
EDIT:
Actually ( "path/to/script" ) is enough.
If you have another file in same directory, you can either do:
bash another_script.sh
or
source another_script.sh
or
. another_script.sh
When you use bash instead of source, the script cannot alter environment of the parent script. The . command is POSIX standard while source command is a more readable bash synonym for . (I prefer source over .). If your script resides elsewhere just provide path to that script. Both relative as well as full path should work.
Depends on.
Briefly...
If you want load variables on current console and execute you may use source myshellfile.sh on your code. Example:
#!/bin/bash
set -x
echo "This is an example of run another INTO this session."
source my_lib_of_variables_and_functions.sh
echo "The function internal_function() is defined into my lib."
returned_value=internal_function()
echo $this_is_an_internal_variable
set +x
If you just want to execute a file and the only thing intersting for you is the result, you can do:
#!/bin/bash
set -x
./executing_only.sh
bash i_can_execute_this_way_too.sh
bash or_this_way.sh
set +x
You can use /bin/sh to call or execute another script (via your actual script):
# cat showdate.sh
#!/bin/bash
echo "Date is: `date`"
# cat mainscript.sh
#!/bin/bash
echo "You are login as: `whoami`"
echo "`/bin/sh ./showdate.sh`" # exact path for the script file
The output would be:
# ./mainscript.sh
You are login as: root
Date is: Thu Oct 17 02:56:36 EDT 2013
First you have to include the file you call:
#!/bin/bash
. includes/included_file.sh
then you call your function like this:
#!/bin/bash
my_called_function
Simple source will help you.
For Ex.
#!/bin/bash
echo "My shell_1"
source my_script1.sh
echo "Back in shell_1"
Just add in a line whatever you would have typed in a terminal to execute the script!
e.g.:
#!bin/bash
./myscript.sh &
if the script to be executed is not in same directory, just use the complete path of the script.
e.g.:`/home/user/script-directory/./myscript.sh &
This was what worked for me, this is the content of the main sh script that executes the other one.
#!/bin/bash
source /path/to/other.sh
The top answer suggests adding #!/bin/bash line to the first line of the sub-script being called. But even if you add the shebang, it is much faster* to run a script in a sub-shell and capture the output:
$(source SCRIPT_NAME)
This works when you want to keep running the same interpreter (e.g. from bash to another bash script) and ensures that the shebang line of the sub-script is not executed.
For example:
#!/bin/bash
SUB_SCRIPT=$(mktemp)
echo "#!/bin/bash" > $SUB_SCRIPT
echo 'echo $1' >> $SUB_SCRIPT
chmod +x $SUB_SCRIPT
if [[ $1 == "--source" ]]; then
for X in $(seq 100); do
MODE=$(source $SUB_SCRIPT "source on")
done
else
for X in $(seq 100); do
MODE=$($SUB_SCRIPT "source off")
done
fi
echo $MODE
rm $SUB_SCRIPT
Output:
~ ❯❯❯ time ./test.sh
source off
./test.sh 0.15s user 0.16s system 87% cpu 0.360 total
~ ❯❯❯ time ./test.sh --source
source on
./test.sh --source 0.05s user 0.06s system 95% cpu 0.114 total
* For example when virus or security tools are running on a device it might take an extra 100ms to exec a new process.
pathToShell="/home/praveen/"
chmod a+x $pathToShell"myShell.sh"
sh $pathToShell"myShell.sh"
#!/bin/bash
# Here you define the absolute path of your script
scriptPath="/home/user/pathScript/"
# Name of your script
scriptName="myscript.sh"
# Here you execute your script
$scriptPath/$scriptName
# Result of script execution
result=$?
chmod a+x /path/to/file-to-be-executed
That was the only thing I needed. Once the script to be executed is made executable like this, you (at least in my case) don't need any other extra operation like sh or ./ while you are calling the script.
Thanks to the comment of #Nathan Lilienthal
Assume the new file is "/home/satya/app/app_specific_env" and the file contents are as follows
#!bin/bash
export FAV_NUMBER="2211"
Append this file reference to ~/.bashrc file
source /home/satya/app/app_specific_env
When ever you restart the machine or relogin, try echo $FAV_NUMBER in the terminal. It will output the value.
Just in case if you want to see the effect right away, source ~/.bashrc in the command line.
There are some problems to import functions from other file.
First: You needn't to do this file executable. Better not to do so!
just add
. file
to import all functions. And all of them will be as if they are defined in your file.
Second: You may be define the function with the same name. It will be overwritten. It's bad. You may declare like that
declare -f new_function_name=old_function_name
and only after that do import.
So you may call old function by new name.
Third: You may import only full list of functions defined in file.
If some not needed you may unset them. But if you rewrite your functions after unset they will be lost. But if you set reference to it as described above you may restore after unset with the same name.
Finally In common procedure of import is dangerous and not so simple. Be careful! You may write script to do this more easier and safe.
If you use only part of functions(not all) better split them in different files. Unfortunately this technique not made well in bash. In python for example and some other script languages it's easy and safe. Possible to make partial import only needed functions with its own names. We all want that in next bush versions will be done the same functionality. But now We must write many additional cod so as to do what you want.
Use backticks.
$ ./script-that-consumes-argument.sh `sh script-that-produces-argument.sh`
Then fetch the output of the producer script as an argument on the consumer script.

Running bash function in command of su

In my bash script, I execute some commands as another user. I want to call a bash function using su.
my_function()
{
do_something
}
su username -c "my_function"
The above script doesn't work. Of course, my_function is not defined inside su. One idea I have is to put the function into a separate file. Do you have a better idea that avoids making another file?
You can export the function to make it available to the subshell:
export -f my_function
su username -c "my_function"
You could enable 'sudo' in your system, and use that instead.
You must have the function in the same scope where you use it. So either place the function inside the quotes, or put the function to a separate script, which you then run with su -c.
Another way could be making cases and passing a parameter to the executed script.
Example could be:
First make a file called "script.sh".
Then insert this code in it:
#!/bin/sh
my_function() {
echo "this is my function."
}
my_second_function() {
echo "this is my second function."
}
case "$1" in
'do_my_function')
my_function
;;
'do_my_second_function')
my_second_function
;;
*) #default execute
my_function
esac
After adding the above code run these commands to see it in action:
root#shell:/# chmod +x script.sh #This will make the file executable
root#shell:/# ./script.sh #This will run the script without any parameters, triggering the default action.
this is my function.
root#shell:/# ./script.sh do_my_second_function #Executing the script with parameter
this function is my second one.
root#shell:/#
To make this work as you required you'll just need to run
su username -c '/path/to/script.sh do_my_second_function'
and everything should be working fine.
Hope this helps :)

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