Comment 5 for bug 1145461

Nitpicking grammar in my own patch...

Here's a slightly better patch, only because man flock(1) clarifies that one can pass only a single command with direct invocation of flock. Below the synopsis are three other quotes from the man page. Only the third form, which is not used by run-one, allows multiple commands to be run.

SYNOPSIS
       flock [-sxon] [-w timeout] lockfile [-c] command...
       flock [-sxon] [-w timeout] lockdir [-c] command...
       flock [-sxun] [-w timeout] fd

Pass a single command to the shell with -c.
The first and second forms wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1).
The third form is convenient inside shell scripts, and is usually used
       the following manner:

       (
         flock -n 9 || exit 1
         # ... commands executed under lock ...
       ) 9>/var/lock/mylockfile

$ diff -Nru a/run-one b/run-one
--- a/run-one 2013-03-04 18:02:15.513983439 -0500
+++ b/run-one 2013-03-05 15:27:46.635948096 -0500
@@ -32,14 +32,15 @@
 mkdir -p "$DIR"

 # Calculate the hash of the command and arguments
+CMD="$@"
 CMDHASH=$(echo "$@" | md5sum | awk '{print $1}')
 FLAG="$DIR/$CMDHASH"

 # Handle run-this-one invocation, by killing matching process first
 case "$(basename $0)" in
  run-one)
- # Run the specified commands, assuming we can flock this command string's hash
- flock -xn "$FLAG" "$@"
+ # Run the specified command, assuming we can flock this command string's hash
+ flock -xn "$FLAG" -c "$CMD"
  ;;
  run-this-one)
   ps="$@"
@@ -58,15 +59,15 @@
   pid=$(lsof "$FLAG" | awk '{print $2}' | grep "^[0-9]") || true
   [ -z "$pid" ] || kill $pid
   sleep 0.1
- # Run the specified commands, assuming we can flock this command string's hash
- flock -xn "$FLAG" "$@"
+ # Run the specified command, assuming we can flock this command string's hash
+ flock -xn "$FLAG" -c "$CMD"
  ;;
  keep-one-running)
   backoff=1
   while true; do
- # Run the specified commands, assuming we can flock this command string's hash
+ # Run the specified command, assuming we can flock this command string's hash
    set +e
- flock -xn "$FLAG" "$@"
+ flock -xn "$FLAG" -c "$CMD"
    if [ "$?" = 0 ]; then
     # Last run finished successfully, reset to minimum back-off of 1 second
     backoff=1