shasum: 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/shasum - from package: perl-Digest-SHA

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

On Debian possible default full paths are:

/usr/bin/shasum - from package: libdigest-sha-perl
/usr/bin/shasum - from package: perl

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

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