How to get caller function call method in bash

Question

Based on the following code below, is it possible to obtain the value of $caller_method from the pseudocode function below whether a function's caller has made a function call normally eg: mytest 1 or using subshell style eg: echo "(mytest 1)".

#!/bin/bash
function mytest() {

      # THIS IS PSEUDOCODE
      if $caller_method=directly; then
         echo "THIS WAS CALLED DIRECTLY"
         # Do other stuff
      elif $caller_method=inside_a_subshell; then
         echo "THIS WAS CALLED INSIDE A SUBSHELL"
         # Do other stuff
      fi
     # END OF PSEUDOCODE
}
    
    # CALLER 
    # Calling mytest directly
    mytest 1
    # Calling mytest inside a subshell
    echo "$(mytest 1)"

expected output:

THIS WAS CALLED DIRECTLY
THIS WAS CALLED INSIDE A SUBSHELL

So, does the mytest() function able to understand or store an information whether it has been called using this method mytest 1 or $(mytest 1) ?

Also, I don't want to have any extra arguments passed from the caller function such as $(mytest 1 call_inside_a_subshell) or mytest 1 call_directly

Vlastimil Burián · Accepted Answer · 2021-06-30 08:21:55Z

2

I just found out this issue is related how to detect if we are in a subshell using a built-in variable $BASHPID How can I detect if I'm in a subshell?

So the code can be written:

#!/bin/bash

function mytest()
{
    if [ "$$" -eq "$BASHPID" ]; then
        echo "THIS WAS CALLED DIRECTLY"
    else
        echo "THIS WAS CALLED INSIDE A SUBSHELL"
    fi
}

# Calling mytest directly
mytest 1
# Calling mytest inside a subshell
echo "$(mytest 1)"

edited Jun 30, 2021 at 8:21

Vlastimil Burián

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answered Jun 30, 2021 at 6:00

MaXi32

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nobody · Accepted Answer · 2021-06-30 06:00:57Z

1

I think it can be done. Try this:

#!/bin/bash

function mytest() {
    # THIS IS PSEUDOCODE
    if [ $ORIGINALBASHPID -eq $BASHPID ]; then
        echo "THIS WAS CALLED DIRECTLY"
        # Do other stuff
    else
        echo "THIS WAS CALLED INSIDE A SUBSHELL"
        # Do other stuff
    fi
    # END OF PSEUDOCODE
}

# CALLER
ORIGINALBASHPID=$BASHPID
# Calling mytest directly
mytest 1
# Calling mytest inside a subshell
echo "$(mytest 1)"

It outputs:

THIS WAS CALLED DIRECTLY
THIS WAS CALLED INSIDE A SUBSHELL

answered Jun 30, 2021 at 6:00

nobody

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