manage a chunk in a conf file

update-conf-file.sh

#!/bin/bash
#
# update-conf-file <file to update> [<file to insert> | <directory>]
#
# This script manages the insertion or update of a singleton region of
# a file. You can use it to insert lines into configuration files, and
# cleanly update them later.
#
# If a file to insert is specified, that file will be cat'd into the
# file to update. If a directory is specified, all files that don't
# begin with "." in that directory will be cat'd instead. If no
# additional argument is given, STDIN is inserted into the file to
# update.

set -e

# Random SHA-1 hashes to tag beginning and end of the manage region.
TAG1="a808aeadec93e8e56f625dc607eccc617a8f6e3a"
TAG2="f1d2d2f924e986ac86fdf7b36c94bcdf32beec15"

## TODO
##
## Implement --help.
## Argument to set comment character.

test "$1" || (cat $0; false)

FILE="$1"

test -x "$FILE" || touch "$FILE" # Create it if it doesn't exist.
test -f "$FILE"
test -w "$FILE"

shift

TEMP_INFILE=`tempfile`
TEMP_OUTFILE=`tempfile`
trap "rm $TEMP_INFILE $TEMP_OUTFILE" EXIT

if [ "$1" ]; then
    if [ -d "$1" ]; then
        cat "$1"/[^.]* > $TEMP_INFILE || true
    else
        cat "$@" > $TEMP_INFILE
    fi
else
    cat > $TEMP_INFILE
fi

cat "$FILE" > $TEMP_OUTFILE

(
awk '          { if (!seen) print $0 }
     /'$TAG1'/ { seen = 1; }
           END { if (!seen) print "# update-conf-file begin '$TAG1'" }' "$FILE"

cat $TEMP_INFILE

awk '/'$TAG2'/ { if (!seen) print $0; seen = 1; }
    !/'$TAG2'/ { if (seen) print $0 }
           END { if (!seen) print "# update-conf-file end   '$TAG2'" }' "$FILE"
) > $TEMP_OUTFILE

cat $TEMP_OUTFILE > "$FILE"