Monthly Archives: June 2017

How to undo a Git commit that was not pushed 7

 in Programming  tagged commit / git / hard / mixed / reset / soft / undo by

To undo a Git commit that was not pushed, you are given a few major options:

  1. Undo the commit but keep all changes staged
  2. Undo the commit and unstage the changes
  3. Undo the commit and lose all changes

Method 1: Undo commit and keep all files staged

In case you just want to undo the commit and change nothing more, you can use


git reset --soft HEAD~;

This is most often used to make a few changes to your latest commit and/or fix your commit message. Leaves working tree as it was before reset.
soft does not touch the index file or the working tree at all (but resets the head to the previous commit). This leaves all your changed files Changes to be committed, as git status would put it.

Method 2: Undo commit and unstage all files

In case you want to undo the last commit and unstage all the files you can use the following


git reset HEAD~;

or


git reset --mixed HEAD~;

mixed will reset the index but not the working tree (i.e., the changed files are preserved but not marked for commit) and reports what has not been updated. This is the default action.

Method 3: Undo the commit and completely remove all changes

The following method will undo the commit and revert all changes so that your state is exactly as it was before you started making changes.


git reset --hard HEAD~;

hard resets the index and working tree. Any changes to tracked files in the working tree since the previous commit are discarded.

 

Note: In case you just want to rewrite the commit message, you could use git –amend instead.

How to get the pid of the last executed command that was sent to the background in a bash shell

 in Bash  tagged $! / background / pid / process by

Recently we came to the need of writing a bash script that needed periodically to check if a specific process, that was started by the script, had ended and restart it (something like watchdog but with not so many features).

To achieve this, we used the one of the shell special parameters, the $!. Like all other special parameters $! may only be referenced and the user cannot make an assignment to it.

($!) Expands to the process ID of the job most recently placed into the background, whether executed as an asynchronous command or using the bg builtin command.

From GNU.org: https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html#index-_0021-1

Example of Usage

In this example we wanted to get the PID of the application called server to be used later on in the script.


server &
echo $!; #This will print the process ID of the 'server' application

C: Implicit declaration of function ‘read’ and ‘write’ 6

 in C  tagged implicit declaration / read / unistd.h / write by

While working on an socket-based application, we received the following warnings from the compiler:

implicit declaration of function 'read'
implicit declaration of function 'write'

read and write functions are declared in unistd.h which we forgot to include in our code.

Adding the directive


#include <unistd.h>

to the source file that used read and/or write removed the warnings.