pltcl: 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/pltcl - from package: plplot-tk

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

On Debian possible default full paths are:

/usr/bin/pltcl - from package: plplot-tcl-bin

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

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