pgsql2shp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/pgsql2shp - from package: postgis

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/pgsql2shp - from package: postgis

You may install the required package with command apt-get install {package}

Error in other languages:
pgsql2shp: bevel nie gevind nie
pgsql2shp: comandă negăsită
pgsql2shp: comando não encontrado
pgsql2shp: commande introuvable
pgsql2shp: command not found
pgsql2shp: käsku ei ole
pgsql2shp: không tìm thấy lệnh
pgsql2shp: komanda nerasta
pgsql2shp: Kommando nicht gefunden.
pgsql2shp: kommandot finns inte
pgsql2shp: komut yok
pgsql2shp: nie znaleziono polecenia
pgsql2shp: níor aimsíodh an t-ordú
pgsql2shp: no se encontró la orden
pgsql2shp: no s'ha trobat l'ordre
pgsql2shp: opdracht niet gevonden
pgsql2shp: parancs nem található
pgsql2shp: perintah tidak ditemukan
pgsql2shp: príkaz nenájdený
pgsql2shp: příkaz nenalezen
pgsql2shp: команда не найдена
pgsql2shp: командата не е открита
pgsql2shp: 命令找不到
pgsql2shp: コマンドが見つかりません