[groff] 12/13: [gdiffmk]: Refactor to stop using expr(1).

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit 173588377b17787785f85ca366303517c21074a7
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Sat Dec 23 17:50:46 2023 -0600

    [gdiffmk]: Refactor to stop using expr(1).
    
    * contrib/gdiffmk/gdiffmk.sh (RequiresArgument): Refactor to use shell
      parameter expansion instead of expr(1), to avoid potential use of
      external command and quirk in FreeBSD's implementation.
    
    * ANNOUNCE:
    * PROBLEMS: Drop caveat.
---
 ANNOUNCE                   |  3 ---
 PROBLEMS                   | 13 -------------
 contrib/gdiffmk/ChangeLog  |  6 ++++++
 contrib/gdiffmk/gdiffmk.sh | 26 +++++++++++++++-----------
 4 files changed, 21 insertions(+), 27 deletions(-)

diff --git a/ANNOUNCE b/ANNOUNCE
index b53af0717..ca0e7b68f 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -138,9 +138,6 @@ o Some portability issues are known to affect groff's 
gdiffmk utility.
   gdiffmk does not work with BusyBox diff (which does not implement GNU
   diff's "-D" option).
 
-  gdiffmk does not work on FreeBSD due to specifics of that platform's
-  expr(1) implementation.
-
 o GNU tools, or otherwise POSIX-conforming ones, are generally required
   to build on Solaris 10 or 11.  See the "PROBLEMS" file in the
   distribution archive.
diff --git a/PROBLEMS b/PROBLEMS
index cdac1d98f..b5a832667 100644
--- a/PROBLEMS
+++ b/PROBLEMS
@@ -40,19 +40,6 @@ Some portability issues are known to affect groff's gdiffmk 
utility.
 - gdiffmk does not work with BusyBox diff (which does not implement GNU
   diff's "-D" option).
 
-- gdiffmk does not work on FreeBSD due to specifics of that platform's
-  expr(1) implementation.
-
-  gdiffmk uses the expr(1) command to parse its arguments.  FreeBSD has
-  extended the syntax of its expr command in a non-backward compatible
-  way that it claims better conforms with POSIX's utility syntax
-  guidelines with respect to option processing: however, POSIX mandates
-  no options for expr.  Other implementations of expr do not support
-  traditional Unix-style options ('-a', '-b', ...), and perhaps as a
-  consequence do not follow FreeBSD's interpretation of the guidelines.
-  You way want to set $EXPR_COMPAT in your shell environment.  We hope
-  to have a workaround for this behavior in a future release.
-
 ----------------------------------------------------------------------
 
 [groff 1.19.2]
diff --git a/contrib/gdiffmk/ChangeLog b/contrib/gdiffmk/ChangeLog
index ebc4bb2f9..aeeb76486 100644
--- a/contrib/gdiffmk/ChangeLog
+++ b/contrib/gdiffmk/ChangeLog
@@ -1,3 +1,9 @@
+2023-12-23  G. Branden Robinson <g.branden.robinson@gmail.com>
+
+       * gdiffmk.sh (RequiresArgument): Refactor to use shell parameter
+       expansion instead of expr(1), to avoid potential use of external
+       command and quirk in FreeBSD's implementation.
+
 2023-12-23  G. Branden Robinson <g.branden.robinson@gmail.com>
 
        * gdiffmk.sh (FileRead, main): Revise wording of diagnostic
diff --git a/contrib/gdiffmk/gdiffmk.sh b/contrib/gdiffmk/gdiffmk.sh
index 2f9a3e784..8945f8543 100644
--- a/contrib/gdiffmk/gdiffmk.sh
+++ b/contrib/gdiffmk/gdiffmk.sh
@@ -141,23 +141,27 @@ DELETEMARK='*'
 MARK1='[['
 MARK2=']]'
 
+# Given an option with an expected argument, echo the option argument.
+# Return 0 if caller should further shift its argument list; 1 if not.
 RequiresArgument () {
-       #       Process flags that take either concatenated or
-       #       separated values.
        case "$1" in
        -??*)
-               expr "$1" : '-.\(.*\)'
+               optarg=${1#-?}
+               option=${option%${optarg}}
+
+               if test -z "${optarg}"
+               then
+                       Exit 2 "option '${option}' requires an argument"
+               fi
+
+               echo "${optarg}"
                return 1
                ;;
+       *)
+               echo "$2"
+               return 0
+               ;;
        esac
-
-       if test $# -lt 2
-       then
-               Exit 2 "option '$1' requires an argument"
-       fi
-
-       echo "$2"
-       return 0
 }
 
 HAVE_TEST_EF_OPTION=@HAVE_TEST_EF_OPTION@