diff --git a/doc/user-guide b/doc/user-guide
index 7e16e81b..91e79757 100644
--- a/doc/user-guide
+++ b/doc/user-guide
@@ -191,6 +191,7 @@ Sortix comes with a number of home-made programs. Here is an overview:
* `true` - exit with a success status
* `type` - type raw characters directly into the terminal
* `uname` - system information
+* `uniq` - report or omit repeated lines
* `uptime` - time since initialization
* `wc` - count words and lines
* `which` - find path to command
diff --git a/utils/.gitignore b/utils/.gitignore
index 26a0a487..ee19cb1e 100644
--- a/utils/.gitignore
+++ b/utils/.gitignore
@@ -39,6 +39,7 @@ time
true
type
uname
+uniq
uptime
wc
which
diff --git a/utils/Makefile b/utils/Makefile
index 3143ed50..a568526a 100644
--- a/utils/Makefile
+++ b/utils/Makefile
@@ -55,6 +55,7 @@ time \
true \
type \
uname \
+uniq \
uptime \
wc \
which \
diff --git a/utils/uniq.cpp b/utils/uniq.cpp
new file mode 100644
index 00000000..ac570529
--- /dev/null
+++ b/utils/uniq.cpp
@@ -0,0 +1,245 @@
+/*******************************************************************************
+
+ Copyright(C) Jonas 'Sortie' Termansen 2014.
+
+ This program is free software: you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by the Free
+ Software Foundation, either version 3 of the License, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ more details.
+
+ You should have received a copy of the GNU General Public License along with
+ this program. If not, see .
+
+ uniq.cpp
+ Report or filter out repeated lines in a file
+
+*******************************************************************************/
+
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+
+// TODO: Implement all the features mandated by POSIX.
+// TODO: Implement the useful GNU extensions.
+
+char* read_line(FILE* fp, const char* fpname, int delim)
+{
+ char* line = NULL;
+ size_t line_size = 0;
+ ssize_t amount = getdelim(&line, &line_size, delim, fp);
+ if ( amount < 0 )
+ {
+ if ( ferror(fp) )
+ error(0, errno, "read: `%s'", fpname);
+ return NULL;
+ }
+ if ( amount && (unsigned char) line[amount-1] == (unsigned char) delim )
+ line[amount-1] = '\0';
+ return line;
+}
+
+static void compact_arguments(int* argc, char*** argv)
+{
+ for ( int i = 0; i < *argc; i++ )
+ {
+ while ( i < *argc && !(*argv)[i] )
+ {
+ for ( int n = i; n < *argc; n++ )
+ (*argv)[n] = (*argv)[n+1];
+ (*argc)--;
+ }
+ }
+}
+
+static void help(FILE* fp, const char* argv0)
+{
+ fprintf(fp, "Usage: %s [OPTION]... [INPUT [OUTPUT]]\n", argv0);
+ fprintf(fp, "Filter adjacent matching lines from INPUT (or standard input),\n");
+ fprintf(fp, "writing to OUTPUT (or standard output).\n");
+ fprintf(fp, "\n");
+ fprintf(fp, "With no options, matching lines are merged to the first occurrence.\n");
+ fprintf(fp, "\n");
+ fprintf(fp, "Mandatory arguments to long options are mandatory for short options too.\n");
+ fprintf(fp, " -c, --count prefix lines by the number of occurrences\n");
+ fprintf(fp, " -d, --repeated only print duplicate lines\n");
+#if 0
+ fprintf(fp, " -D, --all-repeated[=delimit-method] print all duplicate lines\n");
+ fprintf(fp, " delimit-method={none(default),prepend,separate}\n");
+ fprintf(fp, " Delimiting is done with blank lines\n");
+ fprintf(fp, " -f, --skip-fields=N avoid comparing the first N fields\n");
+ fprintf(fp, " -i, --ignore-case ignore differences in case when comparing\n");
+ fprintf(fp, " -s, --skip-chars=N avoid comparing the first N characters\n");
+#endif
+ fprintf(fp, " -u, --unique only print unique lines\n");
+ fprintf(fp, " -z, --zero-terminated end lines with 0 byte, not newline\n");
+#if 0
+ fprintf(fp, " -w, --check-chars=N compare no more than N characters in lines\n");
+#endif
+ fprintf(fp, " --help display this help and exit\n");
+ fprintf(fp, " --version output version information and exit\n");
+ fprintf(fp, "\n");
+#if 0
+ fprintf(fp, "A field is a run of blanks (usually spaces and/or TABs), then non-blank\n");
+ fprintf(fp, "characters. Fields are skipped before chars.\n");
+ fprintf(fp, "\n");
+#endif
+ fprintf(fp, "Note: 'uniq' does not detect repeated lines unless they are adjacent.\n");
+ fprintf(fp, "You may want to sort the input first, or use `sort -u' without `uniq'.\n");
+ fprintf(fp, "Also, comparisons honor the rules specified by `LC_COLLATE'.\n");
+}
+
+static void version(FILE* fp, const char* argv0)
+{
+ fprintf(fp, "%s (Sortix) %s\n", argv0, VERSIONSTR);
+ fprintf(fp, "License GPLv3+: GNU GPL version 3 or later .\n");
+ fprintf(fp, "This is free software: you are free to change and redistribute it.\n");
+ fprintf(fp, "There is NO WARRANTY, to the extent permitted by law.\n");
+}
+
+int main(int argc, char* argv[])
+{
+ setlocale(LC_ALL, "");
+
+ bool count = false;
+ bool delete_singulars = false;
+ bool delete_duplicates = false;
+ bool zero_terminated = false;
+
+ const char* argv0 = argv[0];
+ for ( int i = 1; i < argc; i++ )
+ {
+ const char* arg = argv[i];
+ if ( arg[0] != '-' || !arg[1] )
+ continue;
+ argv[i] = NULL;
+ if ( !strcmp(arg, "--") )
+ break;
+ if ( arg[1] != '-' )
+ {
+ while ( char c = *++arg ) switch ( c )
+ {
+ case 'c': count = true; break;
+ case 'd': delete_singulars = true; break;
+ case 'u': delete_duplicates = true; break;
+ case 'z': zero_terminated = true; break;
+ default:
+ fprintf(stderr, "%s: unknown option -- '%c'\n", argv0, c);
+ help(stderr, argv0);
+ exit(1);
+ }
+ }
+ else if ( !strcmp(arg, "--help") )
+ help(stdout, argv0), exit(0);
+ else if ( !strcmp(arg, "--version") )
+ version(stdout, argv0), exit(0);
+ else if ( !strcmp(arg, "--count") )
+ count = true;
+ else if ( !strcmp(arg, "--repeated") )
+ delete_singulars = true;
+ else if ( !strcmp(arg, "--unique") )
+ delete_duplicates = true;
+ else if ( !strcmp(arg, "--zero-terminated") )
+ zero_terminated = true;
+ else
+ {
+ fprintf(stderr, "%s: unknown option: %s\n", argv0, arg);
+ help(stderr, argv0);
+ exit(1);
+ }
+ }
+
+ compact_arguments(&argc, &argv);
+
+ if ( 4 <= argc )
+ {
+ fprintf(stderr, "%s: extra operand `%s'\n", argv0, argv[3]);
+ fprintf(stderr, "Try `%s --help' for more information.\n", argv0);
+ exit(1);
+ }
+
+ const char* inname = "";
+ const char* outname = "";
+
+ if ( 3 <= argc && !freopen(outname = argv[2], "w", stdout) )
+ error(1, errno, "`%s'", argv[2]);
+
+ if ( 2 <= argc && !freopen(inname = argv[1], "r", stdin) )
+ error(1, errno, "`%s'", argv[1]);
+
+ int delim = zero_terminated ? '\0' : '\n';
+
+ uintmax_t num_repeats = 0;
+ char* prev_line = NULL;
+ while ( true )
+ {
+ char* line = read_line(stdin, inname, delim);
+
+ bool first = !prev_line;
+ bool different = !first && (!line || strcoll(line, prev_line) != 0);
+
+ if ( delete_singulars && delete_duplicates )
+ {
+ }
+ else if ( delete_singulars )
+ {
+ if ( different && 1 < num_repeats )
+ {
+ if ( count )
+ printf("%ju ", num_repeats);
+ fputs(prev_line, stdout);
+ fputc(delim, stdout);
+ }
+ }
+ else if ( delete_duplicates )
+ {
+ if ( different && num_repeats == 1 )
+ {
+ if ( count )
+ printf("%ju ", num_repeats);
+ fputs(prev_line, stdout);
+ fputc(delim, stdout);
+ }
+ }
+ else
+ {
+ if ( count && different )
+ {
+ printf("%ju ", num_repeats);
+ fputs(prev_line, stdout);
+ fputc(delim, stdout);
+ }
+ }
+
+ if ( different )
+ num_repeats = 0;
+
+ if ( !line )
+ break;
+
+ bool original = first || strcoll(line, prev_line) != 0;
+ if ( !count && !delete_singulars && !delete_duplicates && original )
+ {
+ fputs(line, stdout);
+ fputc(delim, stdout);
+ }
+
+ free(prev_line);
+ prev_line = line;
+ num_repeats++;
+ }
+ free(prev_line);
+
+ if ( fflush(stdout) == EOF || ferror(stdout) )
+ return 1;
+
+ return 0;
+}