On-line help info for mlr join --lk "" (#1458)

* Doc info for `mlr join --lk ""` * make dev output
johnkerl · Dec 24, 2023 · e3b98cd · e3b98cd
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diff --git a/docs/src/manpage.md b/docs/src/manpage.md
@@ -1338,6 +1338,8 @@ MILLER(1)                                                            MILLER(1)
          --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                       names from the left file. Automatically includes the join-field name(s). Helpful
                       for when you only want a limited subset of information from the left file.
+                      Tip: you can use --lk "": this means the left file becomes solely a row-selector
+                      for the input files.
          --lp {text}  Additional prefix for non-join output field names from
                       the left file
          --rp {text}  Additional prefix for non-join output field names from

diff --git a/docs/src/manpage.txt b/docs/src/manpage.txt
@@ -1317,6 +1317,8 @@ MILLER(1)                                                            MILLER(1)
          --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                       names from the left file. Automatically includes the join-field name(s). Helpful
                       for when you only want a limited subset of information from the left file.
+                      Tip: you can use --lk "": this means the left file becomes solely a row-selector
+                      for the input files.
          --lp {text}  Additional prefix for non-join output field names from
                       the left file
          --rp {text}  Additional prefix for non-join output field names from

diff --git a/docs/src/reference-verbs.md b/docs/src/reference-verbs.md
@@ -1671,6 +1671,8 @@ Options:
   --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                names from the left file. Automatically includes the join-field name(s). Helpful
                for when you only want a limited subset of information from the left file.
+               Tip: you can use --lk "": this means the left file becomes solely a row-selector
+               for the input files.
   --lp {text}  Additional prefix for non-join output field names from
                the left file
   --rp {text}  Additional prefix for non-join output field names from

diff --git a/man/manpage.txt b/man/manpage.txt
@@ -1317,6 +1317,8 @@ MILLER(1)                                                            MILLER(1)
          --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                       names from the left file. Automatically includes the join-field name(s). Helpful
                       for when you only want a limited subset of information from the left file.
+                      Tip: you can use --lk "": this means the left file becomes solely a row-selector
+                      for the input files.
          --lp {text}  Additional prefix for non-join output field names from
                       the left file
          --rp {text}  Additional prefix for non-join output field names from

diff --git a/man/mlr.1 b/man/mlr.1
@@ -1662,6 +1662,8 @@ Options:
   --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                names from the left file. Automatically includes the join-field name(s). Helpful
                for when you only want a limited subset of information from the left file.
+               Tip: you can use --lk "": this means the left file becomes solely a row-selector
+               for the input files.
   --lp {text}  Additional prefix for non-join output field names from
                the left file
   --rp {text}  Additional prefix for non-join output field names from

diff --git a/pkg/transformers/join.go b/pkg/transformers/join.go
@@ -92,6 +92,8 @@ func transformerJoinUsage(
 	fmt.Fprintf(o, "  --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field\n")
 	fmt.Fprintf(o, "               names from the left file. Automatically includes the join-field name(s). Helpful\n")
 	fmt.Fprintf(o, "               for when you only want a limited subset of information from the left file.\n")
+	fmt.Fprintf(o, "               Tip: you can use --lk \"\": this means the left file becomes solely a row-selector\n")
+	fmt.Fprintf(o, "               for the input files.\n")
 	fmt.Fprintf(o, "  --lp {text}  Additional prefix for non-join output field names from\n")
 	fmt.Fprintf(o, "               the left file\n")
 	fmt.Fprintf(o, "  --rp {text}  Additional prefix for non-join output field names from\n")

diff --git a/test/cases/cli-help/0001/expout b/test/cases/cli-help/0001/expout
@@ -467,6 +467,8 @@ Options:
   --lk|--left-keep-field-names {a,b,c} If supplied, this means keep only the specified field
                names from the left file. Automatically includes the join-field name(s). Helpful
                for when you only want a limited subset of information from the left file.
+               Tip: you can use --lk "": this means the left file becomes solely a row-selector
+               for the input files.
   --lp {text}  Additional prefix for non-join output field names from
                the left file
   --rp {text}  Additional prefix for non-join output field names from