Git Cheat Sheet

Most commonly used git commands

git init
    # initializes an empty git in the current directory

git config -l
git config --global user.name "<your name>"
git config --global user.email "<your email>"
git config --global color.status auto
git config --global color.diff auto
git config --global color.branch auto

git clone <git host>:/repo/<projectName>
    # copy a git repository so you can add to it

git add <file1 file2>
    # adds files to the staging area
git add .
    # recursively add all files under current directory
git add *
    # add all files in current directory only

git checkout -- <file>
    # reverts back the modified file to the one in the repository

git status
    # view the status of your files in the working directory and staging area
git status -s
    # short form. Left column for staging area. Right column for working dir

git diff
    # show diff of unstaged changes
git diff --cached
    # show diff of staged changes
git diff HEAD
    # show diff of all staged or unstaged changes

git commit
    # records a snapshot of the staging area
git commit -a
    # stage modified files before commit. Does not add new files, but removes deleted files from staging area
git commit -m 'commit message goes here'
git commit --amend
    # Update the last commit message
git commit --amend --reset-author
    # Use this if you have changed your user name or email with git config and want to fix this identity for previous commit

git reset --hard HEAD
    # This will throw away any changes you may have added to the git index and as well as any outstanding changes you have in your working tree.
git reset HEAD
    # unstage all changes that were staged. Reset staging area to HEAD
git reset HEAD -- <file1 file2>
    # unstage files. Reset the file to its snapshot in HEAD

git revert HEAD
    # This will create a new commit which undoes the change in HEAD (i.e. the last commit). You will need to enter the message for the new commit.
git revert HEAD^
    # Git will attempt to undo the old change while leaving intact any changes made since then.

git rm <file1 file2>
    # remove files from staging area and working dir
git rm --cached <files>
    # remove files from staging area only
git rm -r subdir/
    # path = * to recursively remove subdirectories from staging area and working dir

git pull

git branch -a
git branch <branchName>
    # create new local branch at your last commit. So all commits of current branch will be copied over to the new branch.
git push origin <branchName>
    # push a new local branch to the server. If you do not explicitly push your new local branches, they stay in your repo and are invisible to others
git pull origin <branchName>
    # pull a remote branch
git branch -d <branchName>
    # delete branch. This command ensures that the changes in the branch (to be deleted) are already in the current branch.
git branch -D <branchName>
    # delete branch. This command will NOT check if the changes in the branch (to be deleted) are already in the current branch.
git push origin :<branchName>
    # will delete the branch on the origin remote
git branch --track <master> <origin/master>
    #Add release branch??
git checkout <branchName>
    # Switch the branch you are currently on
git remote
git remote show <origin>
    # Lists the URL for the remote repository as well as the tracking branch information

git log <release>
git log --name-status
git log -p
git log --pretty=full
git log --no-merges
    # Ignore merges
git tag -l
    # list tag names
git tag -a v1.4 -m 'version 1.4'
    # Create tag with annotation
git tag v1.4
    # Create tag without annotation
git push --tags
    # Push tags to remote
git show <tagname>
    # Show tag and tagger details

#To rename a tag:
git tag NEW OLD
    # First create NEW as an alias of OLD
git tag -d OLD
    # Delete OLD
git push origin :OLD
    # Delete OLD in remote branch

git stash
git stash apply
git stash list
git log stash@{2}
git show stash@{32}
git reflog
git reflog expire --expire=30.days refs/stash

Looking for anything else? Please refer to Git Documentation page.

Simple Chat Program in C (Part 1)

A multi-threaded chat client in C using socket and pthread library

I wrote this code years ago, putting it here because some people may want to get some help in writing server client programs in C using socket programming.

The server and client programs have a few features that you might want to take a look at. I am not going to explain the functionalities here, you can get that fairly easily by just going through the codes, they are bit long, but quite self explanatory. Ask in the comment area if you have any confusion.

The server program

The server basically waits for clients to connect and start passing message among them. Whenever a client connects to this server, it creates a thread to handle the new client, this way, it does not block other clients from connecting. Also the server can take a few commands such as whether you want to exit or not. Here is the source code of the server:

/*
** Author: Zobayer Hasan
** Date: 26th February, 2010
** Copyright: NO COPYRIGHT ISSUES. However, do not copy it.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <netdb.h>
#include <unistd.h>
#include <pthread.h>

#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>

#define IP "127.0.0.1"
#define PORT 8080
#define BACKLOG 10
#define CLIENTS 10

#define BUFFSIZE 1024
#define ALIASLEN 32
#define OPTLEN 16

struct PACKET {
    char option[OPTLEN]; // instruction
    char alias[ALIASLEN]; // client's alias
    char buff[BUFFSIZE]; // payload
};

struct THREADINFO {
    pthread_t thread_ID; // thread's pointer
    int sockfd; // socket file descriptor
    char alias[ALIASLEN]; // client's alias
};

struct LLNODE {
    struct THREADINFO threadinfo;
    struct LLNODE *next;
};

struct LLIST {
    struct LLNODE *head, *tail;
    int size;
};

int compare(struct THREADINFO *a, struct THREADINFO *b) {
    return a->sockfd - b->sockfd;
}

void list_init(struct LLIST *ll) {
    ll->head = ll->tail = NULL;
    ll->size = 0;
}

int list_insert(struct LLIST *ll, struct THREADINFO *thr_info) {
    if(ll->size == CLIENTS) return -1;
    if(ll->head == NULL) {
        ll->head = (struct LLNODE *)malloc(sizeof(struct LLNODE));
        ll->head->threadinfo = *thr_info;
        ll->head->next = NULL;
        ll->tail = ll->head;
    }
    else {
        ll->tail->next = (struct LLNODE *)malloc(sizeof(struct LLNODE));
        ll->tail->next->threadinfo = *thr_info;
        ll->tail->next->next = NULL;
        ll->tail = ll->tail->next;
    }
    ll->size++;
    return 0;
}

int list_delete(struct LLIST *ll, struct THREADINFO *thr_info) {
    struct LLNODE *curr, *temp;
    if(ll->head == NULL) return -1;
    if(compare(thr_info, &ll->head->threadinfo) == 0) {
        temp = ll->head;
        ll->head = ll->head->next;
        if(ll->head == NULL) ll->tail = ll->head;
        free(temp);
        ll->size--;
        return 0;
    }
    for(curr = ll->head; curr->next != NULL; curr = curr->next) {
        if(compare(thr_info, &curr->next->threadinfo) == 0) {
            temp = curr->next;
            if(temp == ll->tail) ll->tail = curr;
            curr->next = curr->next->next;
            free(temp);
            ll->size--;
            return 0;
        }
    }
    return -1;
}

void list_dump(struct LLIST *ll) {
    struct LLNODE *curr;
    struct THREADINFO *thr_info;
    printf("Connection count: %d\n", ll->size);
    for(curr = ll->head; curr != NULL; curr = curr->next) {
        thr_info = &curr->threadinfo;
        printf("[%d] %s\n", thr_info->sockfd, thr_info->alias);
    }
}

int sockfd, newfd;
struct THREADINFO thread_info[CLIENTS];
struct LLIST client_list;
pthread_mutex_t clientlist_mutex;

void *io_handler(void *param);
void *client_handler(void *fd);

int main(int argc, char **argv) {
    int err_ret, sin_size;
    struct sockaddr_in serv_addr, client_addr;
    pthread_t interrupt;

    /* initialize linked list */
    list_init(&client_list);

    /* initiate mutex */
    pthread_mutex_init(&clientlist_mutex, NULL);

    /* open a socket */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        err_ret = errno;
        fprintf(stderr, "socket() failed...\n");
        return err_ret;
    }

    /* set initial values */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    serv_addr.sin_addr.s_addr = inet_addr(IP);
    memset(&(serv_addr.sin_zero), 0, 8);

    /* bind address with socket */
    if(bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(struct sockaddr)) == -1) {
        err_ret = errno;
        fprintf(stderr, "bind() failed...\n");
        return err_ret;
    }

    /* start listening for connection */
    if(listen(sockfd, BACKLOG) == -1) {
        err_ret = errno;
        fprintf(stderr, "listen() failed...\n");
        return err_ret;
    }

    /* initiate interrupt handler for IO controlling */
    printf("Starting admin interface...\n");
    if(pthread_create(&interrupt, NULL, io_handler, NULL) != 0) {
        err_ret = errno;
        fprintf(stderr, "pthread_create() failed...\n");
        return err_ret;
    }

    /* keep accepting connections */
    printf("Starting socket listener...\n");
    while(1) {
        sin_size = sizeof(struct sockaddr_in);
        if((newfd = accept(sockfd, (struct sockaddr *)&client_addr, (socklen_t*)&sin_size)) == -1) {
            err_ret = errno;
            fprintf(stderr, "accept() failed...\n");
            return err_ret;
        }
        else {
            if(client_list.size == CLIENTS) {
                fprintf(stderr, "Connection full, request rejected...\n");
                continue;
            }
            printf("Connection requested received...\n");
            struct THREADINFO threadinfo;
            threadinfo.sockfd = newfd;
            strcpy(threadinfo.alias, "Anonymous");
            pthread_mutex_lock(&clientlist_mutex);
            list_insert(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            pthread_create(&threadinfo.thread_ID, NULL, client_handler, (void *)&threadinfo);
        }
    }

    return 0;
}

void *io_handler(void *param) {
    char option[OPTLEN];
    while(scanf("%s", option)==1) {
        if(!strcmp(option, "exit")) {
            /* clean up */
            printf("Terminating server...\n");
            pthread_mutex_destroy(&clientlist_mutex);
            close(sockfd);
            exit(0);
        }
        else if(!strcmp(option, "list")) {
            pthread_mutex_lock(&clientlist_mutex);
            list_dump(&client_list);
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else {
            fprintf(stderr, "Unknown command: %s...\n", option);
        }
    }
    return NULL;
}

void *client_handler(void *fd) {
    struct THREADINFO threadinfo = *(struct THREADINFO *)fd;
    struct PACKET packet;
    struct LLNODE *curr;
    int bytes, sent;
    while(1) {
        bytes = recv(threadinfo.sockfd, (void *)&packet, sizeof(struct PACKET), 0);
        if(!bytes) {
            fprintf(stderr, "Connection lost from [%d] %s...\n", threadinfo.sockfd, threadinfo.alias);
            pthread_mutex_lock(&clientlist_mutex);
            list_delete(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            break;
        }
        printf("[%d] %s %s %s\n", threadinfo.sockfd, packet.option, packet.alias, packet.buff);
        if(!strcmp(packet.option, "alias")) {
            printf("Set alias to %s\n", packet.alias);
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                if(compare(&curr->threadinfo, &threadinfo) == 0) {
                    strcpy(curr->threadinfo.alias, packet.alias);
                    strcpy(threadinfo.alias, packet.alias);
                    break;
                }
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "whisp")) {
            int i;
            char target[ALIASLEN];
            for(i = 0; packet.buff[i] != ' '; i++); packet.buff[i++] = 0;
            strcpy(target, packet.buff);
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                if(strcmp(target, curr->threadinfo.alias) == 0) {
                    struct PACKET spacket;
                    memset(&spacket, 0, sizeof(struct PACKET));
                    if(!compare(&curr->threadinfo, &threadinfo)) continue;
                    strcpy(spacket.option, "msg");
                    strcpy(spacket.alias, packet.alias);
                    strcpy(spacket.buff, &packet.buff[i]);
                    sent = send(curr->threadinfo.sockfd, (void *)&spacket, sizeof(struct PACKET), 0);
                }
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "send")) {
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                struct PACKET spacket;
                memset(&spacket, 0, sizeof(struct PACKET));
                if(!compare(&curr->threadinfo, &threadinfo)) continue;
                strcpy(spacket.option, "msg");
                strcpy(spacket.alias, packet.alias);
                strcpy(spacket.buff, packet.buff);
                sent = send(curr->threadinfo.sockfd, (void *)&spacket, sizeof(struct PACKET), 0);
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "exit")) {
            printf("[%d] %s has disconnected...\n", threadinfo.sockfd, threadinfo.alias);
            pthread_mutex_lock(&clientlist_mutex);
            list_delete(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            break;
        }
        else {
            fprintf(stderr, "Garbage data from [%d] %s...\n", threadinfo.sockfd, threadinfo.alias);
        }
    }

    /* clean up */
    close(threadinfo.sockfd);

    return NULL;
}

Compile it like this:

gcc server.c -o server -lpthread

Continue to Part 2 : The Client