Initial version.

.github/workflows/mclip.yml

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+---
+name: mclip
+on: push
+permissions:
+  contents: write
+jobs:
+  build:
+    runs-on: ubuntu-latest 
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build
+        run: make build
+
+      - name: Upload 
+        uses: actions/upload-artifact@v3
+        with:
+          name: mclip
+          path: build/mclip
+
+      - name: Release
+        uses: cycjimmy/semantic-release-action@v4
+        env:
+          GH_TOKEN: ${{ secrets.GH_TOKEN }}

.gitignore

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+# Prerequisites
+*.d
+
+# Object files
+*.o
+*.ko
+*.obj
+*.elf
+
+# Linker output
+*.ilk
+*.map
+*.exp
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Libraries
+*.lib
+*.a
+*.la
+*.lo
+
+# Shared objects (inc. Windows DLLs)
+*.dll
+*.so
+*.so.*
+*.dylib
+
+# Executables
+*.exe
+*.out
+*.app
+*.i*86
+*.x86_64
+*.hex
+
+# Debug files
+*.dSYM/
+*.su
+*.idb
+*.pdb
+
+# Kernel Module Compile Results
+*.mod*
+*.cmd
+.tmp_versions/
+modules.order
+Module.symvers
+Mkfile.old
+dkms.conf
+
+# Build dirs
+build/*

.releaserc.yaml

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+---
+branches: 
+  - main
+plugins:
+  - "@semantic-release/commit-analyzer"
+  - "@semantic-release/release-notes-generator"
+  - "@semantic-release/github"
+  - "@semantic-release/changelog"
+tagFormat: ${version}
+dryRun: true
+ci: true

Makefile

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+CC=gcc
+
+all: mclip
+
+clean:
+	rm -rf build
+
+build: main.c
+	mkdir -p build
+	$(CC) -o build/mclip main.c
+
+install: build
+	cp build/mclip /usr/bin

README.md

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+# :clipboard: mclip
+
+mclip (for "**M**emory **Clip**board") is a very simple Linux clipboard manager which stores its data inside a POSIX shared memory object.
+
+Today several clipboad tools exist but almost all of them require a specific dependency (X11, Wayland, Tmux, SSH, etc.). See for example the [Clipboard integration](https://neovim.io/doc/user/provider.html#provider-clipboard) page in the Neovim documentation.
+
+mclip is a tiny binary which only depends on low level Linux system functions like [`shm_open`](https://man7.org/linux/man-pages/man3/shm_open.3.html) and [`mmap`](https://man7.org/linux/man-pages/man2/mmap.2.html). So it should be usable in very basic environments.
+
+## Install
+
+## Usage
+
+This section explains how to use mclip in several tools.
+
+- [CLI](#cli)
+- [Neovim](#neovim)
+- [Zellij](#zellij)
+
+### CLI
+
+Display the help.
+
+```bash
+clip --help
+Usage: mclip [OPTION]
+
+Clipboard which stores its data inside shared memory.
+
+         h-, --help      read text from standard input and write it into the clipboard shared memory (default).
+         i-, --in        read text from standard input and write it into the clipboard shared memory (default).
+         o-, --out       print the content of the clipboard shared memory.
+```
+
+To save text into the clipboard just enter it through stdin.
+
+```bash
+# Using a pipe
+$ echo "Hello world!" | mclip
+
+# Entering characters with the keyboard (press Ctrl+D to finish your input)
+$ mclip
+I can
+enter 
+text 
+on 
+several 
+lines
+<Ctrl+D>
+```
+
+You can finally output the content of the clipboard.
+
+```bash
+$ mclip -o
+Hello world!
+```
+
+### Neovim
+
+[Neovim](https://neovim.io) provides a [Clipboard integration](https://neovim.io/doc/user/provider.html#provider-clipboard) which allows to provide any clipboard tool. 
+
+You can configure mclip as the Neovim clipboard tool using the following Lua configuration object.
+
+```lua
+vim.g.clipboard = {
+    name = "mclip",
+    copy = {
+        ["+"] = "mclip",
+        ["*"] = "mclip",
+    },
+    paste = {
+        ["+"] = "mclip -o",
+        ["*"] = "mclip -o",
+    },
+    cache_enabled = 1,
+}
+```
+
+## Zellij
+
+TODO

main.c

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+#define _GNU_SOURCE
+
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <getopt.h>
+
+static const char SHARED_MEMORY_NAME[] = "/mclip";
+
+/**
+ * Read text from stdin and write into the shared memory.
+ */
+void in() {
+  void *addr = NULL;
+  int fd = 0;
+
+  fd = shm_open(SHARED_MEMORY_NAME, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
+
+  if (fd == -1) {
+    fprintf(stderr, "shm_open() failed\n");
+    exit(1);
+  }
+
+  char characters[2]  = {0};
+
+  int offset = 0;
+  int nb_read = 0;
+  int total_nb_read = 0;
+
+  while(fgets(characters, sizeof(characters), stdin) != NULL) {
+    nb_read = strlen(characters);
+    total_nb_read = total_nb_read + nb_read;
+
+    // Truncate the file to reserve space in it
+    if(ftruncate(fd, total_nb_read) == -1) {
+      fprintf(stderr, "ftruncate() failed\n");
+      exit(1);
+    }
+
+    if (addr != NULL)
+      addr = mremap(addr, offset, total_nb_read, MREMAP_MAYMOVE);
+    else
+      addr = mmap(NULL, total_nb_read, PROT_WRITE, MAP_SHARED, fd, 0);
+
+    sprintf(addr + offset, "%s", characters);
+
+    offset = total_nb_read;
+  }
+
+  munmap(addr, total_nb_read);
+  memset(characters, 0, sizeof(characters));
+
+  return;
+}
+
+/**
+ * Read text from the shared memory and write it to stdout.
+ */
+void out() {
+  struct stat st;
+  int fd = 0;
+  void *addr = NULL;
+
+  fd = shm_open(SHARED_MEMORY_NAME, O_RDONLY, S_IRUSR | S_IWUSR);
+
+  if (fd == -1) {
+    fprintf(stderr, "shm_open() failed\n");
+    exit(1);
+  }
+
+  fstat(fd, &st);
+
+  // The shared memory is empty when it has just been initialized the first time with 'shm_open()'.
+  if (st.st_size != 0) {
+    addr = mmap(NULL, 1024, PROT_READ, MAP_SHARED, fd, 0);
+
+    if (addr == MAP_FAILED) {
+      fprintf(stderr, "mmap() failed\n");
+      exit(1);
+    }
+  }
+
+  printf("%s", (char*) addr);
+}
+
+/**
+ * Display the help.
+ */
+void help() {
+  printf("Usage: mclip [OPTION]\n\n");
+  printf("Clipboard which stores its data inside shared memory.\n\n");
+  printf("\t h-, --help  \t read text from standard input and write it into the clipboard shared memory (default).\n");
+  printf("\t i-, --in    \t read text from standard input and write it into the clipboard shared memory (default).\n");
+  printf("\t o-, --out   \t print the content of the clipboard shared memory.\n\n");
+}
+
+/**
+ * Main entry of the mclip program.
+ *
+ * @param argc Number of arguments.
+ * @param argv Array of arguments.
+ */
+int main(int argc, char *argv[])
+{
+  int option_help = 0;
+  int option_in = 0;
+  int option_out = 0;
+
+  int c;
+  int option_index = 0;
+
+  static struct option long_options[] = {
+    {"help", no_argument, 0, 'h'},
+    {"in",   no_argument, 0, 'i'},
+    {"out",  no_argument, 0, 'o'},
+    {0, 0, 0, 0}
+  };
+
+  while(1) {
+    c = getopt_long(argc, argv, "hio", long_options, &option_index);
+
+    // No more options to read
+    if (c == -1)
+      break;
+
+    switch(c) {
+
+      // --help
+      case 'h':
+        option_help = 1;
+        break;
+
+      // --in
+      case 'i':
+        option_in = 1;
+        break;
+
+      // --out
+      case 'o':
+        option_out = 1;
+        break;
+
+      // Error encountered (i.e. bad option specified)
+      case '?':
+        exit(1);
+    }
+
+  }
+
+  if (option_help == 1 && (option_in == 1 || option_out == 1)) {
+    fprintf(stderr, "The '--help' option cannot be provided with the '--in' or '--out' option!\n");
+    return 1;
+  } else if (option_help == 0 && option_in == 1 && option_out == 1) {
+    fprintf(stderr, "The '--in' and '--out' options cannot be specified together!\n");
+    return 1;
+  } else if (optind < argc) {
+    fprintf(stderr, "Unknown argument speficied '%s'!\n", argv[optind]);
+    return 1;
+  } else if (option_help == 1) {
+    help();
+    return 0;
+  }
+
+  if (option_in == 1 || (option_in == 0 && option_out == 0)) {
+    in();
+  } else if (option_out == 1) {
+    out();
+  } else {
+    fprintf(stderr, "Unknown program state!\n");
+    return 1;
+  }
+
+  return 0;
+}