Add string split --fields

doc_src/cmds/string-split.rst

@@ -8,8 +8,8 @@ Synopsis
 
 ::
 
-    string split [(-m | --max) MAX] [(-n | --no-empty)] [(-q | --quiet)] [(-r | --right)] SEP [STRING...]
+    string split [(-f | --fields) FIELDS] [(-m | --max) MAX] [(-n | --no-empty)] [(-q | --quiet)] [(-r | --right)] SEP [STRING...]
-    string split0 [(-m | --max) MAX] [(-n | --no-empty)] [(-q | --quiet)] [(-r | --right)] [STRING...]
+    string split0 [(-f | --fields) FIELDS] [(-m | --max) MAX] [(-n | --no-empty)] [(-q | --quiet)] [(-r | --right)] [STRING...]
 
 .. END SYNOPSIS
 
@@ -18,7 +18,7 @@ Description
 
 .. BEGIN DESCRIPTION
 
-``string split`` splits each STRING on the separator SEP, which can be an empty string. If ``-m`` or ``--max`` is specified, at most MAX splits are done on each STRING. If ``-r`` or ``--right`` is given, splitting is performed right-to-left. This is useful in combination with ``-m`` or ``--max``. With ``-n`` or ``--no-empty``, empty results are excluded from consideration (e.g. ``hello\n\nworld`` would expand to two strings and not three). Exit status: 0 if at least one split was performed, or 1 otherwise.
+``string split`` splits each STRING on the separator SEP, which can be an empty string. If ``-m`` or ``--max`` is specified, at most MAX splits are done on each STRING. If ``-r`` or ``--right`` is given, splitting is performed right-to-left. This is useful in combination with ``-m`` or ``--max``. With ``-n`` or ``--no-empty``, empty results are excluded from consideration (e.g. ``hello\n\nworld`` would expand to two strings and not three). Use ``-f`` or ``--fields`` to print out specific fields. Exit status: 0 if at least one split was performed, or 1 otherwise.
 
 See also the ``--delimiter`` option of the :ref:`read <cmd-read>` command.
 
@@ -49,6 +49,11 @@ Examples
     b
     c
 
+    >_ string split -f1,3 '' abc
+    a
+    c
+
+
 NUL Delimited Examples
 ^^^^^^^^^^^^^^^^^^^^^^
 

share/completions/string.fish

@@ -13,6 +13,7 @@ complete -x -c string -n "test (count (commandline -opc)) -ge 2; and contains --
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a split
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a split0
 complete -x -c string -n 'test (count (commandline -opc)) -ge 2; and string match -qr split0\?\$ -- (commandline -opc)[2]' -s m -l max -a "(seq 1 10)" -d "Specify maximum number of splits"
+complete -x -c string -n 'test (count (commandline -opc)) -ge 2; and string match -qr split0\?\$ -- (commandline -opc)[2]' -s f -l fields -a "(seq 1 10)" -d "Specify fields"
 complete -f -c string -n 'test (count (commandline -opc)) -ge 2; and string match -qr split0\?\$ -- (commandline -opc)[2]' -s r -l right -d "Split right-to-left"
 complete -f -c string -n 'test (count (commandline -opc)) -ge 2; and string match -qr split0\?\$ -- (commandline -opc)[2]' -s n -l no-empty -d "Empty results excluded"
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a collect

src/builtin_string.cpp

@@ -155,6 +155,7 @@ typedef struct {  //!OCLINT(too many fields)
     bool style_valid = false;
     bool no_empty_valid = false;
     bool no_trim_newlines_valid = false;
+    bool fields_valid = false;
 
     bool all = false;
     bool entire = false;
@@ -177,6 +178,8 @@ typedef struct {  //!OCLINT(too many fields)
     long start = 0;
     long end = 0;
 
+    std::vector<int> fields;
+
     const wchar_t *chars_to_trim = L" \f\n\r\t\v";
     const wchar_t *arg1 = nullptr;
     const wchar_t *arg2 = nullptr;
@@ -267,6 +270,19 @@ static int handle_flag_f(wchar_t **argv, parser_t &parser, io_streams_t &streams
     if (opts->filter_valid) {
         opts->filter = true;
         return STATUS_CMD_OK;
+    } else if (opts->fields_valid) {
+        for (const wcstring &s : split_string(w.woptarg, L',')) {
+            int field = fish_wcstoi(wcsdup(s.c_str()));
+            if (field <= 0 || field == INT_MIN || errno == ERANGE) {
+                string_error(streams, _(L"%ls: Invalid fields value '%ls'\n"), argv[0], w.woptarg);
+                return STATUS_INVALID_ARGS;
+            } else if (errno) {
+                string_error(streams, BUILTIN_ERR_NOT_NUMBER, argv[0], w.woptarg);
+                return STATUS_INVALID_ARGS;
+            }
+            opts->fields.push_back(field);
+        }
+        return STATUS_CMD_OK;
     }
     string_unknown_option(parser, streams, argv[0], argv[w.woptind - 1]);
     return STATUS_INVALID_ARGS;
@@ -423,6 +439,7 @@ static wcstring construct_short_opts(options_t *opts) {  //!OCLINT(high npath co
     if (opts->end_valid) short_opts.append(L"e:");
     if (opts->no_empty_valid) short_opts.append(L"n");
     if (opts->no_trim_newlines_valid) short_opts.append(L"N");
+    if (opts->fields_valid) short_opts.append(L"f:");
     return short_opts;
 }
 
@@ -450,6 +467,7 @@ static const struct woption long_options[] = {{L"all", no_argument, nullptr, 'a'
                                               {L"start", required_argument, nullptr, 's'},
                                               {L"style", required_argument, nullptr, 1},
                                               {L"no-trim-newlines", no_argument, nullptr, 'N'},
+                                              {L"fields", required_argument, nullptr, 'f'},
                                               {nullptr, 0, nullptr, 0}};
 
 static const std::unordered_map<char, decltype(*handle_flag_N)> flag_to_function = {
@@ -1083,6 +1101,7 @@ static int string_split_maybe0(parser_t &parser, io_streams_t &streams, int argc
     opts.max_valid = true;
     opts.max = LONG_MAX;
     opts.no_empty_valid = true;
+    opts.fields_valid = true;
     int optind;
     int retval = parse_opts(&opts, &optind, is_split0 ? 0 : 1, argc, argv, parser, streams);
     if (retval != STATUS_CMD_OK) return retval;
@@ -1121,8 +1140,17 @@ static int string_split_maybe0(parser_t &parser, io_streams_t &streams, int argc
             if (splits.back().empty()) splits.pop_back();
         }
         auto &buff = streams.out.buffer();
-        for (const wcstring &split : splits) {
+        if (opts.fields.size() > 0) {
-            buff.append(split, separation_type_t::explicitly);
+            for (const auto &field : opts.fields) {
+                // field indexing starts from 1
+                if (field - 1 < (long)split_count) {
+                    buff.append(splits.at(field - 1), separation_type_t::explicitly);
+                }
+            }
+        } else {
+            for (const wcstring &split : splits) {
+                buff.append(split, separation_type_t::explicitly);
+            }
         }
     }
 

tests/checks/string.fish

@@ -88,6 +88,16 @@ string split "" abc
 # CHECK: b
 # CHECK: c
 
+string split --fields=2 "" abc
+# CHECK: b
+
+string split --fields=2,3 "" abc
+# CHECK: b
+# CHECK: c
+
+string split --fields=2,9 "" abc
+# CHECK: b
+
 seq 3 | string join ...
 # CHECK: 1...2...3