Left side of pipe is the subshell?

by

From the bash man page: “Each command in a pipeline is executed as a separate process (i.e., in a subshell).” I suppose it would be possible to execute one component of a pipeline in the current shell (i.e. the first, or the last, or maybe one in the middle), it doesn’t play favorites like this: they all execute in subshells. If you modify your script like this:

#!/bin/bash
declare -i i=0
function f1()
{
    let i++
    echo "In f1, SUBSHELL: $BASH_SUBSHELL, i=$i" >&2
}

f1
f1 | f1 | f1

echo "at end, i=$i"

it prints:

In f1, SUBSHELL: 0, i=1
In f1, SUBSHELL: 1, i=2
In f1, SUBSHELL: 1, i=2
In f1, SUBSHELL: 1, i=2
at end, i=1

because all 3 invocations of f1 in the pipeline run in subshells.

More Related Contents:

  1. How to pipe multiple commands into a single command in the shell? (sh, bash, …)
  2. Get exit code from subshell through the pipes
  3. bash piping prevents global variable assignment
  4. Difference between sh and Bash
  5. Expansion of variables inside single quotes in a command in Bash
  6. Pass commands as input to another command (su, ssh, sh, etc)
  7. Why do you need ./ (dot-slash) before executable or script name to run it in bash?
  8. What is the cleanest way to ssh and run multiple commands in Bash?
  9. How to pipe input to a Bash while loop and preserve variables after loop ends
  10. Bash variable scope
  11. How to remove files starting with double hyphen?
  12. How to get the primary IP address of the local machine on Linux and OS X? [closed]
  13. How to suppress Terminated message after killing in bash?
  14. How to make the ‘cut’ command treat same sequental delimiters as one?
  15. How do I get bc(1) to print the leading zero?
  16. Set a parent shell’s variable from a subshell
  17. Copy folder recursively, excluding some folders
  18. Variable interpolation in the shell
  19. How to do a logical OR operation for integer comparison in shell scripting?
  20. Bash indirect variable referencing
  21. bash background process modify global variable
  22. How do I pause my shell script for a second before continuing?
  23. What does ” 2>&1 ” mean?
  24. Bash regex =~ operator
  25. How do I check if a directory exists or not in a Bash shell script?
  26. Bash script to receive and repass quoted parameters
  27. Validate date format in a shell script
  28. Multiplication on command line terminal
  29. Why doesn’t **sort** sort the same on every machine?
  30. Using a variable’s value as password for scp, ssh etc. instead of prompting for user input every time

Leave a Comment