General options: (P - pgsql2shp, S - shp2pgsql)

P
  S
  S
  S
  S
  S
  S
P  
P S
P
  S
  S
  S
  S
P
P
P
  S
P
  S
  S
  S
  S
P S

  -b
  -s srid
  (-d|a|c|p) 
      -d   
      -a  
      -c  
      -p 
  -f filename
  -g geometry_column_name
  -h hostname
  -D
  -k
  -i 
  -I 
  -p port
  -P password
  -r 
  -S
  -u user 
  -w  
  -W 
  -N 
  -n  
  -? 

Use a binary cursor.
Set the SRID field. If not specified it defaults to -1.
These are mutually exclusive options:
Drops the table, then recreates it and populates it with current shape file data.
Appends shape file into current table, must be exactly the same table schema.
Creates a new table and populates it, default if you do not specify any options.
Prepare mode, only creates the table.
Use this option to specify the name of the file to create
Specify the name of the geometry column to be (S) created (P) exported.
Specify db server host name defaults to localhost.
Use postgresql dump format (defaults to sql insert statments).
Keep postgresql identifiers case.
Use int4 type for all integer dbf fields.
Create a GiST index on the geometry column.
Allows you to specify a database port other than the default. Defaults to 5432.
Connect to the database with the specified password.
Raw mode. Do not unescape attribute names and not skip the 'gid' attribute.
Generate simple geometries instead of MULTI geometries.
Connect to the database as the specified user. 
Use wkt format (for postgis-0.x support - drops M - drifts coordinates).
encoding The character encoding of Shape's attribute column. (default : "ASCII")
policy Specify NULL geometries handling policy (insert,skip,abort)
Only import DBF file.
Display this help screen

PSQL Connection options:
  -h, --host=HOSTNAME      database server host or socket directory
  -p, --port=PORT          database server port number
  -U, --username=NAME      connect as specified database user
  -W, --password           force password prompt (should happen automatically)
  -e, --exit-on-error      exit on error, default is to continue

If no input file name is supplied, then standard input is used.

Loading data with shp2pgsql

Load data into PostgreSQL from ESRI shape file
shp2pgsql -s 4326 neighborhoods public.neighborhoods > neighborhoods.sql
psql -h myserver -d mydb -U myuser -f neighborhoods.sql

Do above in one step
shp2pgsql -s 4326 neighborhoods public.neighborhoods | psql -h myserver -d mydb -U myuser

Sample linux sh script to load tiger 2007 massachusetts edges and landmark points
TMPDIR="/gis_data/staging"
STATEDIR="/gis_data/25_MASSACHUSETTS"
STATESCHEMA="ma"
DB="tiger"
USER_NAME="tigeruser"
cd $STATEDIR
#unzip files into temp directory
for z in */*.zip; do unzip -o -d $TMPDIR $z; done 
for z in *.zip; do unzip -o -d $TMPDIR $z; done

#prepare the tables don't load data
#force non-multi and set the geometry column name to the_geom_4269, dbf is in latin1 encoding
shp2pgsql -s 4269 -g the_geom_4269 -S -W "latin1" -p fe_2007_25025_edges.shp ${STATESCHEMA}.edges | psql -U $USER_NAME -d $DB
shp2pgsql -s 4269 -g the_geom_4269 -S -W "latin1" -p fe_2007_25025_pointlm.shp ${STATESCHEMA}.pointlm | psql -U $USER_NAME -d $DB

#loop thru pointlm and edges county tables and append to respective ma.pointlm ma.edges tables
for t in pointlm edges;
do
 for z in *${t}.dbf;
  do 
	shp2pgsql  -s 4269 -g the_geom_4269 -S -W "latin1" -a $z ${STATE_SCHEMA}.${t} | psql -d $DB -U $USER_NAME;  
  done
done

Outputing to ESRI Shapefile/DBF with pgsql2shp

Export query to a shape file called jpnei.shp/dbf
pgsql2shp -f "/path/to/jpnei" -h myserver -u apguser -P apgpassword mygisdb 
	"SELECT neigh_name, the_geom FROM neighborhoods WHERE neigh_name = 'Jamaica Plain'"
	
Export a table in ma schema called streets to streets.shp/dbf
pgsql2shp -f "/path/to/streets" -h myserver -u apguser -P apgpassword mygisdb ma.streets