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The `trap` Command in Bash


The trap command in Bash allows you to specify commands that will be executed when the shell receives a specific signal. This can be useful for performing tasks like cleaning up temporary files.

The trap command has the following syntax:

trap [COMMANDS] [SIGNALS]

Here, COMMANDS is a list of one or more commands that should be executed when the shell receives the specified SIGNALS. SIGNALS is a list of signals for which the COMMANDS should be executed.

The trap command can be used the same ways as the defer keyword in Go and the cleanup pattern in Rust. They are all used to specify code that should be executed at a later time, typically for the purpose of cleaning up resources.

For example, we want to set the core.quotepath option in Git to false and then reset it to its original value when the script finishes executing:

#!/bin/bash

# Save the current value of the core.quotepath option
original_quotepath=$(git config --get --null --local core.quotepath)

# Set the core.quotepath option to true
git config --local core.quotepath false

# Register a cleanup function to reset the core.quotepath option
cleanup() {
  if [ -n "$original_quotepath" ]
  then
    git config --local core.quotepath "$original_quotepath"
  else
    # Unset the core.quotepath option if it was originally unset
    git config --unset --local core.quotepath
  fi
}
trap cleanup EXIT

# ...

In this way, the trap command allows us to specify cleanup tasks that should be performed when the shell exits, regardless of whether the script exits successfully or not. This can be useful for ensuring that our scripts do not leave behind any temporary files or other resources that could potentially cause problems.