When ‘--help’ is given, just run ‘man’ to show the manual page

I.e. do what git does.  I'm too lazy to keep the builtin help text up
to date :-)

Also add ‘--help’ to various commands that lacked it
(e.g. nix-collect-garbage).

src/nix-env/Makefile.am

@@ -1,16 +1,11 @@
 bin_PROGRAMS = nix-env
 
-nix_env_SOURCES = nix-env.cc profiles.cc profiles.hh user-env.cc user-env.hh help.txt
+nix_env_SOURCES = nix-env.cc profiles.cc profiles.hh user-env.cc user-env.hh
 
 nix_env_LDADD = ../libmain/libmain.la ../libexpr/libexpr.la \
  ../libstore/libstore.la ../libutil/libutil.la \
  ../boost/format/libformat.la
 
-nix-env.o: help.txt.hh
-
-%.txt.hh: %.txt
-	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
-
 AM_CXXFLAGS = \
  -I$(srcdir)/.. \
  -I$(srcdir)/../libutil -I$(srcdir)/../libstore \

src/nix-env/help.txt

@@ -1,77 +0,0 @@
-Usage: nix-env [OPTIONS...] [ARGUMENTS...]
-
-`nix-env' is a tool to manipulate Nix user environments.
-
-Operations:
-
-  --install / -i: add derivations to the user environment
-  --upgrade / -u: upgrade derivation in the user environment
-  --set: create a user environment containing a single derivation
-  --uninstall / -e: remove derivations from the user environment
-  --query / -q: perform a query on an environment or Nix expression
-  --set-flag NAME VALUE: set derivation meta-attribute to given value
-
-The previous operations take a list of derivation names.  The special
-name `*' may be used to indicate all derivations.
-
-  --switch-profile / -S [FILE]: switch to specified profile
-  --switch-generation / -G NUMBER: switch to specified generation of profile
-  --rollback: switch to the previous generation
-  --list-generations: list available generations of a profile
-  --delete-generations GENERATIONS...: deleted listed generations,
-      `old' for all non-current generations
-  
-  --version: output version information
-  --help: display help
-
-Install / upgrade / uninstall flags:
-
-  --dry-run: show what would be done, but don't do it
-
-Installation sources:
-
-  --from-expression / -E EXPR...: evaluate expressions specified on
-      the command line; expressions should be functions that take the
-      default Nix expression as an argument
-  --from-profile PROFILE NAMES...: copy named packages from PROFILE
-  --attr / -A ATTRS...: select attributes by name from the default Nix
-      expression
-
-Upgrade flags:
-
-  --lt: upgrade if the current version is older (default)
-  --leq: upgrade if the current version is older or equal
-  --eq: "upgrade" if the current version is equal
-  --always: upgrade regardless of current version
-
-Query sources:
-
-  --installed: use installed derivations (default)
-  --available / -a: use derivations available in Nix expression
-
-Query flags:
-
-  --xml: show output in XML format
-  --status / -s: print installed/present status
-  --no-name: hide derivation names
-  --attr-path / -P: shows the unambiguous attribute name of the
-      derivation which can be used when installing with -A
-  --system: print the platform type of the derivation 
-  --compare-versions / -c: compare version to available or installed
-  --drv-path: print path of derivation
-  --out-path: print path of derivation output
-  --description: print description
-  --meta: print all meta attributes (only with --xml)
-
-Options:
-
-  --profile / -p LINK: use specified profile instead of target of ~/.nix-profile
-  --file / -f FILE: use Nix expression FILE for installation, etc.
-  --verbose / -v: verbose operation (may be repeated)
-  --keep-failed / -K: keep temporary directories of failed builds
-  --keep-going / -k: build as many dependencies as possible, even if
-      some dependencies fail to build
-  --preserve-installed: do not replace currently installed versions in `-i'
-  --system-filter SYSTEM: only use derivations for specified platform
-  --prebuilt-only / -b: only use derivations whose prebuilt binaries are
-      available on this machine or are downloadable

src/nix-env/nix-env.cc

@@ -4,7 +4,6 @@
 #include "misc.hh"
 #include "shared.hh"
 #include "eval.hh"
-#include "help.txt.hh"
 #include "get-drvs.hh"
 #include "attr-path.hh"
 #include "common-opts.hh"
@@ -66,7 +65,7 @@ typedef void (* Operation) (Globals & globals,
 
 void printHelp()
 {
-    cout << string((char *) helpText);
+    showManPage("nix-env");
 }