File: sh.mkln

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##
##  mkln -- Make link with calculation of relative paths
##  Copyright (c) 1998-2008 Ralf S. Engelschall <rse@engelschall.com>
##
##  This file is part of shtool and free software; you can redistribute
##  it and/or modify it under the terms of the GNU General Public
##  License as published by the Free Software Foundation; either version
##  2 of the License, or (at your option) any later version.
##
##  This file is distributed in the hope that it will be useful,
##  but WITHOUT ANY WARRANTY; without even the implied warranty of
##  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
##  General Public License for more details.
##
##  You should have received a copy of the GNU General Public License
##  along with this program; if not, write to the Free Software
##  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
##  USA, or contact Ralf S. Engelschall <rse@engelschall.com>.
##

str_tool="mkln"
str_usage="[-t|--trace] [-f|--force] [-s|--symbolic] <src-path> [<src-path> ...] <dst-path>"
arg_spec="2+"
opt_spec="t.f.s."
opt_alias="t:trace,f:force,s:symbolic"
opt_t=no
opt_f=no
opt_s=no

. ./sh.common

#   determine source(s) and destination
args=$#
srcs=""
while [ $# -gt 1 ]; do
    srcs="$srcs $1"
    shift
done
dst="$1"
if [ ! -d $dst ]; then
    if [ $args -gt 2 ]; then
        echo "$msgprefix:Error: multiple sources not allowed when target isn't a directory" 1>&2
        shtool_exit 1
    fi
fi

#   determine link options
lnopt=""
if [ ".$opt_f" = .yes ]; then
    lnopt="$lnopt -f"
fi
if [ ".$opt_s" = .yes ]; then
    lnopt="$lnopt -s"
fi

#   iterate over sources
for src in $srcs; do
    #   determine if one of the paths is an absolute path,
    #   because then we _have_ to use an absolute symlink
    oneisabs=0
    srcisabs=0
    dstisabs=0
    case $src in
        /* ) oneisabs=1; srcisabs=1 ;;
    esac
    case $dst in
        /* ) oneisabs=1; dstisabs=1 ;;
    esac

    #   split source and destination into dir and base name
    if [ -d $src ]; then
        srcdir=`echo $src | sed -e 's;/*$;;'`
        srcbase=""
    else
        srcdir=`echo  $src | sed -e 's;^[^/]*$;;' -e 's;^\(.*/\)[^/]*$;\1;' -e 's;\(.\)/$;\1;'`
        srcbase=`echo $src | sed -e 's;.*/\([^/]*\)$;\1;'`
    fi
    if [ -d $dst ]; then
        dstdir=`echo $dst | sed -e 's;/*$;;'`
        dstbase=""
    else
        dstdir=`echo  $dst | sed -e 's;^[^/]*$;;' -e 's;^\(.*/\)[^/]*$;\1;' -e 's;\(.\)/$;\1;'`
        dstbase=`echo $dst | sed -e 's;.*/\([^/]*\)$;\1;'`
    fi

    #   consistency check
    if [ ".$dstdir" != . ]; then
        if [ ! -d $dstdir ]; then
            echo "$msgprefix:Error: destination directory not found: $dstdir" 1>&2
            shtool_exit 1
        fi
    fi

    #   make sure the source is reachable from the destination
    if [ $dstisabs = 1 ]; then
        if [ $srcisabs = 0 ]; then
            if [ ".$srcdir" = . ]; then
                srcdir="`pwd | sed -e 's;/*$;;'`"
                srcisabs=1
                oneisabs=1
            elif [ -d $srcdir ]; then
                srcdir="`cd $srcdir; pwd | sed -e 's;/*$;;'`"
                srcisabs=1
                oneisabs=1
            fi
        fi
    fi

    #   split away a common prefix
    prefix=""
    if [ ".$srcdir" = ".$dstdir" ] && [ ".$srcdir" != . ]; then
        prefix="$srcdir/"
        srcdir=""
        dstdir=""
    else
        while [ ".$srcdir" != . ] && [ ".$dstdir" != . ]; do
            presrc=`echo $srcdir | sed -e 's;^\([^/]*\)/.*;\1;'`
            predst=`echo $dstdir | sed -e 's;^\([^/]*\)/.*;\1;'`
            if [ ".$presrc" != ".$predst" ]; then
                break
            fi
            prefix="$prefix$presrc/"
            srcdir=`echo $srcdir | sed -e 's;^[^/]*/*;;'`
            dstdir=`echo $dstdir | sed -e 's;^[^/]*/*;;'`
        done
    fi

    #   destination prefix is just the common prefix
    dstpre="$prefix"

    #   determine source prefix which is the reverse directory
    #   step-up corresponding to the destination directory
    srcpre=""
    allow_relative_srcpre=no
    if [ ".$prefix" != . ] && [ ".$prefix" != ./ ]; then
        allow_relative_srcpre=yes
    fi
    if [ $oneisabs = 0 ]; then
        allow_relative_srcpre=yes
    fi
    if [ ".$opt_s" != .yes ]; then
        allow_relative_srcpre=no
    fi
    if [ ".$allow_relative_srcpre" = .yes ]; then
        pl="$dstdir/"
        OIFS="$IFS"; IFS='/'
        for pe in $pl; do
            [ ".$pe" = .  ] && continue
            [ ".$pe" = .. ] && continue
            srcpre="../$srcpre"
        done
        IFS="$OIFS"
    else
        if [ $srcisabs = 1 ]; then
            srcpre="$prefix"
        fi
    fi

    #   determine destination symlink name
    if [ ".$dstbase" = . ]; then
        if [ ".$srcbase" != . ]; then
            dstbase="$srcbase"
        else
            dstbase=`echo "$prefix$srcdir" | sed -e 's;/*$;;' -e 's;.*/\([^/]*\)$;\1;'`
        fi
    fi

    #   now finalize source and destination directory paths
    srcdir=`echo $srcdir | sed -e 's;\([^/]\)$;\1/;'`
    dstdir=`echo $dstdir | sed -e 's;\([^/]\)$;\1/;'`

    #   run the final link command
    if [ ".$opt_t" = .yes ]; then
        echo "ln$lnopt $srcpre$srcdir$srcbase $dstpre$dstdir$dstbase"
    fi
    eval ln$lnopt $srcpre$srcdir$srcbase $dstpre$dstdir$dstbase
done

shtool_exit 0

##
##  manual page
##

=pod

=head1 NAME

B<shtool-mkln> - B<GNU shtool> enhanced ln(1) replacement

=head1 SYNOPSIS

B<shtool mkln>
[B<-t>|B<--trace>]
[B<-f>|B<--force>]
[B<-s>|B<--symbolic>]
I<src-path> [I<src-path> ...]
I<dst-path>

=head1 DESCRIPTION

This is a ln(1) style command. It is enhanced to provide automatic
calculation and usage of relative links with the shortest possible path,
if possible. Usually if I<src-path> and I<dst-path> are not absolute
paths or at least they share a common prefix except the root directory
(``C</>''). When more than one I<src-path> is specified, all of them are
linked into I<dst-path>.

=head1 OPTIONS

The following command line options are available.

=over 4

=item B<-t>, B<--trace>

Enable the output of the essential shell commands which are executed.

=item B<-f>, B<--force>

Force the creation of the link even if it exists. Default is to fail
with error.

=item B<-s>, B<--symbolic>

Create a symbolic link instead of a hard-link.

=back

=head1 EXAMPLE

 #   shell script
 shtool mkln -s foo/bar baz/quux

=head1 HISTORY

The B<GNU shtool> B<fixperm> command was originally written by Ralf S.
Engelschall E<lt>rse@engelschall.comE<gt> in 1998 for I<ePerl>.

=head1 SEE ALSO

shtool(1), ln(1).

=cut